zig

blob aa6c2dea (326437B) - Raw

---

 const std = @import("std");
 const builtin = @import("builtin");
 const Allocator = std.mem.Allocator;
 const ArrayList = std.ArrayList;
 const assert = std.debug.assert;
 const testing = std.testing;
 const leb = std.leb;
 const mem = std.mem;
 const wasm = std.wasm;
 const log = std.log.scoped(.codegen);
 
 const codegen = @import("../../codegen.zig");
 const Module = @import("../../Module.zig");
 const InternPool = @import("../../InternPool.zig");
 const Decl = Module.Decl;
 const Type = @import("../../type.zig").Type;
 const Value = @import("../../value.zig").Value;
 const Compilation = @import("../../Compilation.zig");
 const LazySrcLoc = Module.LazySrcLoc;
 const link = @import("../../link.zig");
 const TypedValue = @import("../../TypedValue.zig");
 const Air = @import("../../Air.zig");
 const Liveness = @import("../../Liveness.zig");
 const target_util = @import("../../target.zig");
 const Mir = @import("Mir.zig");
 const Emit = @import("Emit.zig");
 const abi = @import("abi.zig");
 const Alignment = InternPool.Alignment;
 const errUnionPayloadOffset = codegen.errUnionPayloadOffset;
 const errUnionErrorOffset = codegen.errUnionErrorOffset;
 
 /// Wasm Value, created when generating an instruction
 const WValue = union(enum) {
     /// `WValue` which has been freed and may no longer hold
     /// any references.
     dead: void,
     /// May be referenced but is unused
     none: void,
     /// The value lives on top of the stack
     stack: void,
     /// Index of the local
     local: struct {
         /// Contains the index to the local
         value: u32,
         /// The amount of instructions referencing this `WValue`
         references: u32,
     },
     /// An immediate 32bit value
     imm32: u32,
     /// An immediate 64bit value
     imm64: u64,
     /// Index into the list of simd128 immediates. This `WValue` is
     /// only possible in very rare cases, therefore it would be
     /// a waste of memory to store the value in a 128 bit integer.
     imm128: u32,
     /// A constant 32bit float value
     float32: f32,
     /// A constant 64bit float value
     float64: f64,
     /// A value that represents a pointer to the data section
     /// Note: The value contains the symbol index, rather than the actual address
     /// as we use this to perform the relocation.
     memory: u32,
     /// A value that represents a parent pointer and an offset
     /// from that pointer. i.e. when slicing with constant values.
     memory_offset: struct {
         /// The symbol of the parent pointer
         pointer: u32,
         /// Offset will be set as addend when relocating
         offset: u32,
     },
     /// Represents a function pointer
     /// In wasm function pointers are indexes into a function table,
     /// rather than an address in the data section.
     function_index: u32,
     /// Offset from the bottom of the virtual stack, with the offset
     /// pointing to where the value lives.
     stack_offset: struct {
         /// Contains the actual value of the offset
         value: u32,
         /// The amount of instructions referencing this `WValue`
         references: u32,
     },
 
     /// Returns the offset from the bottom of the stack. This is useful when
     /// we use the load or store instruction to ensure we retrieve the value
     /// from the correct position, rather than the value that lives at the
     /// bottom of the stack. For instances where `WValue` is not `stack_value`
     /// this will return 0, which allows us to simply call this function for all
     /// loads and stores without requiring checks everywhere.
     fn offset(value: WValue) u32 {
         switch (value) {
             .stack_offset => |stack_offset| return stack_offset.value,
             .dead => unreachable,
             else => return 0,
         }
     }
 
     /// Promotes a `WValue` to a local when given value is on top of the stack.
     /// When encountering a `local` or `stack_offset` this is essentially a no-op.
     /// All other tags are illegal.
     fn toLocal(value: WValue, gen: *CodeGen, ty: Type) InnerError!WValue {
         switch (value) {
             .stack => {
                 const new_local = try gen.allocLocal(ty);
                 try gen.addLabel(.local_set, new_local.local.value);
                 return new_local;
             },
             .local, .stack_offset => return value,
             else => unreachable,
         }
     }
 
     /// Marks a local as no longer being referenced and essentially allows
     /// us to re-use it somewhere else within the function.
     /// The valtype of the local is deducted by using the index of the given `WValue`.
     fn free(value: *WValue, gen: *CodeGen) void {
         if (value.* != .local) return;
         const local_value = value.local.value;
         const reserved = gen.args.len + @intFromBool(gen.return_value != .none);
         if (local_value < reserved + 2) return; // reserved locals may never be re-used. Also accounts for 2 stack locals.
 
         const index = local_value - reserved;
         const valtype = @as(wasm.Valtype, @enumFromInt(gen.locals.items[index]));
         switch (valtype) {
             .i32 => gen.free_locals_i32.append(gen.gpa, local_value) catch return, // It's ok to fail any of those, a new local can be allocated instead
             .i64 => gen.free_locals_i64.append(gen.gpa, local_value) catch return,
             .f32 => gen.free_locals_f32.append(gen.gpa, local_value) catch return,
             .f64 => gen.free_locals_f64.append(gen.gpa, local_value) catch return,
             .v128 => gen.free_locals_v128.append(gen.gpa, local_value) catch return,
         }
         log.debug("freed local ({d}) of type {}", .{ local_value, valtype });
         value.* = .dead;
     }
 };
 
 /// Wasm ops, but without input/output/signedness information
 /// Used for `buildOpcode`
 const Op = enum {
     @"unreachable",
     nop,
     block,
     loop,
     @"if",
     @"else",
     end,
     br,
     br_if,
     br_table,
     @"return",
     call,
     call_indirect,
     drop,
     select,
     local_get,
     local_set,
     local_tee,
     global_get,
     global_set,
     load,
     store,
     memory_size,
     memory_grow,
     @"const",
     eqz,
     eq,
     ne,
     lt,
     gt,
     le,
     ge,
     clz,
     ctz,
     popcnt,
     add,
     sub,
     mul,
     div,
     rem,
     @"and",
     @"or",
     xor,
     shl,
     shr,
     rotl,
     rotr,
     abs,
     neg,
     ceil,
     floor,
     trunc,
     nearest,
     sqrt,
     min,
     max,
     copysign,
     wrap,
     convert,
     demote,
     promote,
     reinterpret,
     extend,
 };
 
 /// Contains the settings needed to create an `Opcode` using `buildOpcode`.
 ///
 /// The fields correspond to the opcode name. Here is an example
 ///          i32_trunc_f32_s
 ///          ^   ^     ^   ^
 ///          |   |     |   |
 ///   valtype1   |     |   |
 ///     = .i32   |     |   |
 ///              |     |   |
 ///             op     |   |
 ///       = .trunc     |   |
 ///                    |   |
 ///             valtype2   |
 ///               = .f32   |
 ///                        |
 ///                width   |
 ///               = null   |
 ///                        |
 ///                   signed
 ///                   = true
 ///
 /// There can be missing fields, here are some more examples:
 ///   i64_load8_u
 ///     --> .{ .valtype1 = .i64, .op = .load, .width = 8, signed = false }
 ///   i32_mul
 ///     --> .{ .valtype1 = .i32, .op = .trunc }
 ///   nop
 ///     --> .{ .op = .nop }
 const OpcodeBuildArguments = struct {
     /// First valtype in the opcode (usually represents the type of the output)
     valtype1: ?wasm.Valtype = null,
     /// The operation (e.g. call, unreachable, div, min, sqrt, etc.)
     op: Op,
     /// Width of the operation (e.g. 8 for i32_load8_s, 16 for i64_extend16_i32_s)
     width: ?u8 = null,
     /// Second valtype in the opcode name (usually represents the type of the input)
     valtype2: ?wasm.Valtype = null,
     /// Signedness of the op
     signedness: ?std.builtin.Signedness = null,
 };
 
 /// Helper function that builds an Opcode given the arguments needed
 fn buildOpcode(args: OpcodeBuildArguments) wasm.Opcode {
     switch (args.op) {
         .@"unreachable" => return .@"unreachable",
         .nop => return .nop,
         .block => return .block,
         .loop => return .loop,
         .@"if" => return .@"if",
         .@"else" => return .@"else",
         .end => return .end,
         .br => return .br,
         .br_if => return .br_if,
         .br_table => return .br_table,
         .@"return" => return .@"return",
         .call => return .call,
         .call_indirect => return .call_indirect,
         .drop => return .drop,
         .select => return .select,
         .local_get => return .local_get,
         .local_set => return .local_set,
         .local_tee => return .local_tee,
         .global_get => return .global_get,
         .global_set => return .global_set,
 
         .load => if (args.width) |width| switch (width) {
             8 => switch (args.valtype1.?) {
                 .i32 => if (args.signedness.? == .signed) return .i32_load8_s else return .i32_load8_u,
                 .i64 => if (args.signedness.? == .signed) return .i64_load8_s else return .i64_load8_u,
                 .f32, .f64, .v128 => unreachable,
             },
             16 => switch (args.valtype1.?) {
                 .i32 => if (args.signedness.? == .signed) return .i32_load16_s else return .i32_load16_u,
                 .i64 => if (args.signedness.? == .signed) return .i64_load16_s else return .i64_load16_u,
                 .f32, .f64, .v128 => unreachable,
             },
             32 => switch (args.valtype1.?) {
                 .i64 => if (args.signedness.? == .signed) return .i64_load32_s else return .i64_load32_u,
                 .i32 => return .i32_load,
                 .f32 => return .f32_load,
                 .f64, .v128 => unreachable,
             },
             64 => switch (args.valtype1.?) {
                 .i64 => return .i64_load,
                 .f64 => return .f64_load,
                 else => unreachable,
             },
             else => unreachable,
         } else switch (args.valtype1.?) {
             .i32 => return .i32_load,
             .i64 => return .i64_load,
             .f32 => return .f32_load,
             .f64 => return .f64_load,
             .v128 => unreachable, // handled independently
         },
         .store => if (args.width) |width| {
             switch (width) {
                 8 => switch (args.valtype1.?) {
                     .i32 => return .i32_store8,
                     .i64 => return .i64_store8,
                     .f32, .f64, .v128 => unreachable,
                 },
                 16 => switch (args.valtype1.?) {
                     .i32 => return .i32_store16,
                     .i64 => return .i64_store16,
                     .f32, .f64, .v128 => unreachable,
                 },
                 32 => switch (args.valtype1.?) {
                     .i64 => return .i64_store32,
                     .i32 => return .i32_store,
                     .f32 => return .f32_store,
                     .f64, .v128 => unreachable,
                 },
                 64 => switch (args.valtype1.?) {
                     .i64 => return .i64_store,
                     .f64 => return .f64_store,
                     else => unreachable,
                 },
                 else => unreachable,
             }
         } else {
             switch (args.valtype1.?) {
                 .i32 => return .i32_store,
                 .i64 => return .i64_store,
                 .f32 => return .f32_store,
                 .f64 => return .f64_store,
                 .v128 => unreachable, // handled independently
             }
         },
 
         .memory_size => return .memory_size,
         .memory_grow => return .memory_grow,
 
         .@"const" => switch (args.valtype1.?) {
             .i32 => return .i32_const,
             .i64 => return .i64_const,
             .f32 => return .f32_const,
             .f64 => return .f64_const,
             .v128 => unreachable, // handled independently
         },
 
         .eqz => switch (args.valtype1.?) {
             .i32 => return .i32_eqz,
             .i64 => return .i64_eqz,
             .f32, .f64, .v128 => unreachable,
         },
         .eq => switch (args.valtype1.?) {
             .i32 => return .i32_eq,
             .i64 => return .i64_eq,
             .f32 => return .f32_eq,
             .f64 => return .f64_eq,
             .v128 => unreachable, // handled independently
         },
         .ne => switch (args.valtype1.?) {
             .i32 => return .i32_ne,
             .i64 => return .i64_ne,
             .f32 => return .f32_ne,
             .f64 => return .f64_ne,
             .v128 => unreachable, // handled independently
         },
 
         .lt => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_lt_s else return .i32_lt_u,
             .i64 => if (args.signedness.? == .signed) return .i64_lt_s else return .i64_lt_u,
             .f32 => return .f32_lt,
             .f64 => return .f64_lt,
             .v128 => unreachable, // handled independently
         },
         .gt => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_gt_s else return .i32_gt_u,
             .i64 => if (args.signedness.? == .signed) return .i64_gt_s else return .i64_gt_u,
             .f32 => return .f32_gt,
             .f64 => return .f64_gt,
             .v128 => unreachable, // handled independently
         },
         .le => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_le_s else return .i32_le_u,
             .i64 => if (args.signedness.? == .signed) return .i64_le_s else return .i64_le_u,
             .f32 => return .f32_le,
             .f64 => return .f64_le,
             .v128 => unreachable, // handled independently
         },
         .ge => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_ge_s else return .i32_ge_u,
             .i64 => if (args.signedness.? == .signed) return .i64_ge_s else return .i64_ge_u,
             .f32 => return .f32_ge,
             .f64 => return .f64_ge,
             .v128 => unreachable, // handled independently
         },
 
         .clz => switch (args.valtype1.?) {
             .i32 => return .i32_clz,
             .i64 => return .i64_clz,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .ctz => switch (args.valtype1.?) {
             .i32 => return .i32_ctz,
             .i64 => return .i64_ctz,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .popcnt => switch (args.valtype1.?) {
             .i32 => return .i32_popcnt,
             .i64 => return .i64_popcnt,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
 
         .add => switch (args.valtype1.?) {
             .i32 => return .i32_add,
             .i64 => return .i64_add,
             .f32 => return .f32_add,
             .f64 => return .f64_add,
             .v128 => unreachable, // handled independently
         },
         .sub => switch (args.valtype1.?) {
             .i32 => return .i32_sub,
             .i64 => return .i64_sub,
             .f32 => return .f32_sub,
             .f64 => return .f64_sub,
             .v128 => unreachable, // handled independently
         },
         .mul => switch (args.valtype1.?) {
             .i32 => return .i32_mul,
             .i64 => return .i64_mul,
             .f32 => return .f32_mul,
             .f64 => return .f64_mul,
             .v128 => unreachable, // handled independently
         },
 
         .div => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_div_s else return .i32_div_u,
             .i64 => if (args.signedness.? == .signed) return .i64_div_s else return .i64_div_u,
             .f32 => return .f32_div,
             .f64 => return .f64_div,
             .v128 => unreachable, // handled independently
         },
         .rem => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_rem_s else return .i32_rem_u,
             .i64 => if (args.signedness.? == .signed) return .i64_rem_s else return .i64_rem_u,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
 
         .@"and" => switch (args.valtype1.?) {
             .i32 => return .i32_and,
             .i64 => return .i64_and,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .@"or" => switch (args.valtype1.?) {
             .i32 => return .i32_or,
             .i64 => return .i64_or,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .xor => switch (args.valtype1.?) {
             .i32 => return .i32_xor,
             .i64 => return .i64_xor,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
 
         .shl => switch (args.valtype1.?) {
             .i32 => return .i32_shl,
             .i64 => return .i64_shl,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .shr => switch (args.valtype1.?) {
             .i32 => if (args.signedness.? == .signed) return .i32_shr_s else return .i32_shr_u,
             .i64 => if (args.signedness.? == .signed) return .i64_shr_s else return .i64_shr_u,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .rotl => switch (args.valtype1.?) {
             .i32 => return .i32_rotl,
             .i64 => return .i64_rotl,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .rotr => switch (args.valtype1.?) {
             .i32 => return .i32_rotr,
             .i64 => return .i64_rotr,
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
 
         .abs => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_abs,
             .f64 => return .f64_abs,
             .v128 => unreachable, // handled independently
         },
         .neg => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_neg,
             .f64 => return .f64_neg,
             .v128 => unreachable, // handled independently
         },
         .ceil => switch (args.valtype1.?) {
             .i64 => unreachable,
             .i32 => return .f32_ceil, // when valtype is f16, we store it in i32.
             .f32 => return .f32_ceil,
             .f64 => return .f64_ceil,
             .v128 => unreachable, // handled independently
         },
         .floor => switch (args.valtype1.?) {
             .i64 => unreachable,
             .i32 => return .f32_floor, // when valtype is f16, we store it in i32.
             .f32 => return .f32_floor,
             .f64 => return .f64_floor,
             .v128 => unreachable, // handled independently
         },
         .trunc => switch (args.valtype1.?) {
             .i32 => if (args.valtype2) |valty| switch (valty) {
                 .i32 => unreachable,
                 .i64 => unreachable,
                 .f32 => if (args.signedness.? == .signed) return .i32_trunc_f32_s else return .i32_trunc_f32_u,
                 .f64 => if (args.signedness.? == .signed) return .i32_trunc_f64_s else return .i32_trunc_f64_u,
                 .v128 => unreachable, // handled independently
             } else return .f32_trunc, // when no valtype2, it's an f16 instead which is stored in an i32.
             .i64 => switch (args.valtype2.?) {
                 .i32 => unreachable,
                 .i64 => unreachable,
                 .f32 => if (args.signedness.? == .signed) return .i64_trunc_f32_s else return .i64_trunc_f32_u,
                 .f64 => if (args.signedness.? == .signed) return .i64_trunc_f64_s else return .i64_trunc_f64_u,
                 .v128 => unreachable, // handled independently
             },
             .f32 => return .f32_trunc,
             .f64 => return .f64_trunc,
             .v128 => unreachable, // handled independently
         },
         .nearest => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_nearest,
             .f64 => return .f64_nearest,
             .v128 => unreachable, // handled independently
         },
         .sqrt => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_sqrt,
             .f64 => return .f64_sqrt,
             .v128 => unreachable, // handled independently
         },
         .min => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_min,
             .f64 => return .f64_min,
             .v128 => unreachable, // handled independently
         },
         .max => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_max,
             .f64 => return .f64_max,
             .v128 => unreachable, // handled independently
         },
         .copysign => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => return .f32_copysign,
             .f64 => return .f64_copysign,
             .v128 => unreachable, // handled independently
         },
 
         .wrap => switch (args.valtype1.?) {
             .i32 => switch (args.valtype2.?) {
                 .i32 => unreachable,
                 .i64 => return .i32_wrap_i64,
                 .f32, .f64 => unreachable,
                 .v128 => unreachable, // handled independently
             },
             .i64, .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
         .convert => switch (args.valtype1.?) {
             .i32, .i64 => unreachable,
             .f32 => switch (args.valtype2.?) {
                 .i32 => if (args.signedness.? == .signed) return .f32_convert_i32_s else return .f32_convert_i32_u,
                 .i64 => if (args.signedness.? == .signed) return .f32_convert_i64_s else return .f32_convert_i64_u,
                 .f32, .f64 => unreachable,
                 .v128 => unreachable, // handled independently
             },
             .f64 => switch (args.valtype2.?) {
                 .i32 => if (args.signedness.? == .signed) return .f64_convert_i32_s else return .f64_convert_i32_u,
                 .i64 => if (args.signedness.? == .signed) return .f64_convert_i64_s else return .f64_convert_i64_u,
                 .f32, .f64 => unreachable,
                 .v128 => unreachable, // handled independently
             },
             .v128 => unreachable, // handled independently
         },
         .demote => if (args.valtype1.? == .f32 and args.valtype2.? == .f64) return .f32_demote_f64 else unreachable,
         .promote => if (args.valtype1.? == .f64 and args.valtype2.? == .f32) return .f64_promote_f32 else unreachable,
         .reinterpret => switch (args.valtype1.?) {
             .i32 => if (args.valtype2.? == .f32) return .i32_reinterpret_f32 else unreachable,
             .i64 => if (args.valtype2.? == .f64) return .i64_reinterpret_f64 else unreachable,
             .f32 => if (args.valtype2.? == .i32) return .f32_reinterpret_i32 else unreachable,
             .f64 => if (args.valtype2.? == .i64) return .f64_reinterpret_i64 else unreachable,
             .v128 => unreachable, // handled independently
         },
         .extend => switch (args.valtype1.?) {
             .i32 => switch (args.width.?) {
                 8 => if (args.signedness.? == .signed) return .i32_extend8_s else unreachable,
                 16 => if (args.signedness.? == .signed) return .i32_extend16_s else unreachable,
                 else => unreachable,
             },
             .i64 => switch (args.width.?) {
                 8 => if (args.signedness.? == .signed) return .i64_extend8_s else unreachable,
                 16 => if (args.signedness.? == .signed) return .i64_extend16_s else unreachable,
                 32 => if (args.signedness.? == .signed) return .i64_extend32_s else unreachable,
                 else => unreachable,
             },
             .f32, .f64 => unreachable,
             .v128 => unreachable, // handled independently
         },
     }
 }
 
 test "Wasm - buildOpcode" {
     // Make sure buildOpcode is referenced, and test some examples
     const i32_const = buildOpcode(.{ .op = .@"const", .valtype1 = .i32 });
     const end = buildOpcode(.{ .op = .end });
     const local_get = buildOpcode(.{ .op = .local_get });
     const i64_extend32_s = buildOpcode(.{ .op = .extend, .valtype1 = .i64, .width = 32, .signedness = .signed });
     const f64_reinterpret_i64 = buildOpcode(.{ .op = .reinterpret, .valtype1 = .f64, .valtype2 = .i64 });
 
     try testing.expectEqual(@as(wasm.Opcode, .i32_const), i32_const);
     try testing.expectEqual(@as(wasm.Opcode, .end), end);
     try testing.expectEqual(@as(wasm.Opcode, .local_get), local_get);
     try testing.expectEqual(@as(wasm.Opcode, .i64_extend32_s), i64_extend32_s);
     try testing.expectEqual(@as(wasm.Opcode, .f64_reinterpret_i64), f64_reinterpret_i64);
 }
 
 /// Hashmap to store generated `WValue` for each `Air.Inst.Ref`
 pub const ValueTable = std.AutoArrayHashMapUnmanaged(Air.Inst.Ref, WValue);
 
 const CodeGen = @This();
 
 /// Reference to the function declaration the code
 /// section belongs to
 decl: *Decl,
 decl_index: InternPool.DeclIndex,
 /// Current block depth. Used to calculate the relative difference between a break
 /// and block
 block_depth: u32 = 0,
 air: Air,
 liveness: Liveness,
 gpa: mem.Allocator,
 debug_output: codegen.DebugInfoOutput,
 func_index: InternPool.Index,
 /// Contains a list of current branches.
 /// When we return from a branch, the branch will be popped from this list,
 /// which means branches can only contain references from within its own branch,
 /// or a branch higher (lower index) in the tree.
 branches: std.ArrayListUnmanaged(Branch) = .{},
 /// Table to save `WValue`'s generated by an `Air.Inst`
 // values: ValueTable,
 /// Mapping from Air.Inst.Index to block ids
 blocks: std.AutoArrayHashMapUnmanaged(Air.Inst.Index, struct {
     label: u32,
     value: WValue,
 }) = .{},
 /// `bytes` contains the wasm bytecode belonging to the 'code' section.
 code: *ArrayList(u8),
 /// The index the next local generated will have
 /// NOTE: arguments share the index with locals therefore the first variable
 /// will have the index that comes after the last argument's index
 local_index: u32 = 0,
 /// The index of the current argument.
 /// Used to track which argument is being referenced in `airArg`.
 arg_index: u32 = 0,
 /// If codegen fails, an error messages will be allocated and saved in `err_msg`
 err_msg: *Module.ErrorMsg,
 /// List of all locals' types generated throughout this declaration
 /// used to emit locals count at start of 'code' section.
 locals: std.ArrayListUnmanaged(u8),
 /// List of simd128 immediates. Each value is stored as an array of bytes.
 /// This list will only be populated for 128bit-simd values when the target features
 /// are enabled also.
 simd_immediates: std.ArrayListUnmanaged([16]u8) = .{},
 /// The Target we're emitting (used to call intInfo)
 target: std.Target,
 /// Represents the wasm binary file that is being linked.
 bin_file: *link.File.Wasm,
 /// List of MIR Instructions
 mir_instructions: std.MultiArrayList(Mir.Inst) = .{},
 /// Contains extra data for MIR
 mir_extra: std.ArrayListUnmanaged(u32) = .{},
 /// When a function is executing, we store the the current stack pointer's value within this local.
 /// This value is then used to restore the stack pointer to the original value at the return of the function.
 initial_stack_value: WValue = .none,
 /// The current stack pointer substracted with the stack size. From this value, we will calculate
 /// all offsets of the stack values.
 bottom_stack_value: WValue = .none,
 /// Arguments of this function declaration
 /// This will be set after `resolveCallingConventionValues`
 args: []WValue = &.{},
 /// This will only be `.none` if the function returns void, or returns an immediate.
 /// When it returns a pointer to the stack, the `.local` tag will be active and must be populated
 /// before this function returns its execution to the caller.
 return_value: WValue = .none,
 /// The size of the stack this function occupies. In the function prologue
 /// we will move the stack pointer by this number, forward aligned with the `stack_alignment`.
 stack_size: u32 = 0,
 /// The stack alignment, which is 16 bytes by default. This is specified by the
 /// tool-conventions: https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md
 /// and also what the llvm backend will emit.
 /// However, local variables or the usage of `@setAlignStack` can overwrite this default.
 stack_alignment: Alignment = .@"16",
 
 // For each individual Wasm valtype we store a seperate free list which
 // allows us to re-use locals that are no longer used. e.g. a temporary local.
 /// A list of indexes which represents a local of valtype `i32`.
 /// It is illegal to store a non-i32 valtype in this list.
 free_locals_i32: std.ArrayListUnmanaged(u32) = .{},
 /// A list of indexes which represents a local of valtype `i64`.
 /// It is illegal to store a non-i64 valtype in this list.
 free_locals_i64: std.ArrayListUnmanaged(u32) = .{},
 /// A list of indexes which represents a local of valtype `f32`.
 /// It is illegal to store a non-f32 valtype in this list.
 free_locals_f32: std.ArrayListUnmanaged(u32) = .{},
 /// A list of indexes which represents a local of valtype `f64`.
 /// It is illegal to store a non-f64 valtype in this list.
 free_locals_f64: std.ArrayListUnmanaged(u32) = .{},
 /// A list of indexes which represents a local of valtype `v127`.
 /// It is illegal to store a non-v128 valtype in this list.
 free_locals_v128: std.ArrayListUnmanaged(u32) = .{},
 
 /// When in debug mode, this tracks if no `finishAir` was missed.
 /// Forgetting to call `finishAir` will cause the result to not be
 /// stored in our `values` map and therefore cause bugs.
 air_bookkeeping: @TypeOf(bookkeeping_init) = bookkeeping_init,
 
 const bookkeeping_init = if (builtin.mode == .Debug) @as(usize, 0) else {};
 
 const InnerError = error{
     OutOfMemory,
     /// An error occurred when trying to lower AIR to MIR.
     CodegenFail,
     /// Compiler implementation could not handle a large integer.
     Overflow,
 };
 
 pub fn deinit(func: *CodeGen) void {
     // in case of an error and we still have branches
     for (func.branches.items) |*branch| {
         branch.deinit(func.gpa);
     }
     func.branches.deinit(func.gpa);
     func.blocks.deinit(func.gpa);
     func.locals.deinit(func.gpa);
     func.simd_immediates.deinit(func.gpa);
     func.mir_instructions.deinit(func.gpa);
     func.mir_extra.deinit(func.gpa);
     func.free_locals_i32.deinit(func.gpa);
     func.free_locals_i64.deinit(func.gpa);
     func.free_locals_f32.deinit(func.gpa);
     func.free_locals_f64.deinit(func.gpa);
     func.free_locals_v128.deinit(func.gpa);
     func.* = undefined;
 }
 
 /// Sets `err_msg` on `CodeGen` and returns `error.CodegenFail` which is caught in link/Wasm.zig
 fn fail(func: *CodeGen, comptime fmt: []const u8, args: anytype) InnerError {
     const mod = func.bin_file.base.comp.module.?;
     const src = LazySrcLoc.nodeOffset(0);
     const src_loc = src.toSrcLoc(func.decl, mod);
     func.err_msg = try Module.ErrorMsg.create(func.gpa, src_loc, fmt, args);
     return error.CodegenFail;
 }
 
 /// Resolves the `WValue` for the given instruction `inst`
 /// When the given instruction has a `Value`, it returns a constant instead
 fn resolveInst(func: *CodeGen, ref: Air.Inst.Ref) InnerError!WValue {
     var branch_index = func.branches.items.len;
     while (branch_index > 0) : (branch_index -= 1) {
         const branch = func.branches.items[branch_index - 1];
         if (branch.values.get(ref)) |value| {
             return value;
         }
     }
 
     // when we did not find an existing instruction, it
     // means we must generate it from a constant.
     // We always store constants in the most outer branch as they must never
     // be removed. The most outer branch is always at index 0.
     const gop = try func.branches.items[0].values.getOrPut(func.gpa, ref);
     assert(!gop.found_existing);
 
     const mod = func.bin_file.base.comp.module.?;
     const val = (try func.air.value(ref, mod)).?;
     const ty = func.typeOf(ref);
     if (!ty.hasRuntimeBitsIgnoreComptime(mod) and !ty.isInt(mod) and !ty.isError(mod)) {
         gop.value_ptr.* = WValue{ .none = {} };
         return gop.value_ptr.*;
     }
 
     // When we need to pass the value by reference (such as a struct), we will
     // leverage `generateSymbol` to lower the constant to bytes and emit it
     // to the 'rodata' section. We then return the index into the section as `WValue`.
     //
     // In the other cases, we will simply lower the constant to a value that fits
     // into a single local (such as a pointer, integer, bool, etc).
     const result = if (isByRef(ty, mod)) blk: {
         const sym_index = try func.bin_file.lowerUnnamedConst(.{ .ty = ty, .val = val }, func.decl_index);
         break :blk WValue{ .memory = sym_index };
     } else try func.lowerConstant(val, ty);
 
     gop.value_ptr.* = result;
     return result;
 }
 
 fn finishAir(func: *CodeGen, inst: Air.Inst.Index, result: WValue, operands: []const Air.Inst.Ref) void {
     assert(operands.len <= Liveness.bpi - 1);
     var tomb_bits = func.liveness.getTombBits(inst);
     for (operands) |operand| {
         const dies = @as(u1, @truncate(tomb_bits)) != 0;
         tomb_bits >>= 1;
         if (!dies) continue;
         processDeath(func, operand);
     }
 
     // results of `none` can never be referenced.
     if (result != .none) {
         assert(result != .stack); // it's illegal to store a stack value as we cannot track its position
         const branch = func.currentBranch();
         branch.values.putAssumeCapacityNoClobber(inst.toRef(), result);
     }
 
     if (builtin.mode == .Debug) {
         func.air_bookkeeping += 1;
     }
 }
 
 const Branch = struct {
     values: ValueTable = .{},
 
     fn deinit(branch: *Branch, gpa: Allocator) void {
         branch.values.deinit(gpa);
         branch.* = undefined;
     }
 };
 
 inline fn currentBranch(func: *CodeGen) *Branch {
     return &func.branches.items[func.branches.items.len - 1];
 }
 
 const BigTomb = struct {
     gen: *CodeGen,
     inst: Air.Inst.Index,
     lbt: Liveness.BigTomb,
 
     fn feed(bt: *BigTomb, op_ref: Air.Inst.Ref) void {
         const dies = bt.lbt.feed();
         if (!dies) return;
         // This will be a nop for interned constants.
         processDeath(bt.gen, op_ref);
     }
 
     fn finishAir(bt: *BigTomb, result: WValue) void {
         assert(result != .stack);
         if (result != .none) {
             bt.gen.currentBranch().values.putAssumeCapacityNoClobber(bt.inst.toRef(), result);
         }
 
         if (builtin.mode == .Debug) {
             bt.gen.air_bookkeeping += 1;
         }
     }
 };
 
 fn iterateBigTomb(func: *CodeGen, inst: Air.Inst.Index, operand_count: usize) !BigTomb {
     try func.currentBranch().values.ensureUnusedCapacity(func.gpa, operand_count + 1);
     return BigTomb{
         .gen = func,
         .inst = inst,
         .lbt = func.liveness.iterateBigTomb(inst),
     };
 }
 
 fn processDeath(func: *CodeGen, ref: Air.Inst.Ref) void {
     if (ref.toIndex() == null) return;
     // Branches are currently only allowed to free locals allocated
     // within their own branch.
     // TODO: Upon branch consolidation free any locals if needed.
     const value = func.currentBranch().values.getPtr(ref) orelse return;
     if (value.* != .local) return;
     const reserved_indexes = func.args.len + @intFromBool(func.return_value != .none);
     if (value.local.value < reserved_indexes) {
         return; // function arguments can never be re-used
     }
     log.debug("Decreasing reference for ref: %{d}, using local '{d}'", .{ @intFromEnum(ref.toIndex().?), value.local.value });
     value.local.references -= 1; // if this panics, a call to `reuseOperand` was forgotten by the developer
     if (value.local.references == 0) {
         value.free(func);
     }
 }
 
 /// Appends a MIR instruction and returns its index within the list of instructions
 fn addInst(func: *CodeGen, inst: Mir.Inst) error{OutOfMemory}!void {
     try func.mir_instructions.append(func.gpa, inst);
 }
 
 fn addTag(func: *CodeGen, tag: Mir.Inst.Tag) error{OutOfMemory}!void {
     try func.addInst(.{ .tag = tag, .data = .{ .tag = {} } });
 }
 
 fn addExtended(func: *CodeGen, opcode: wasm.MiscOpcode) error{OutOfMemory}!void {
     const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
     try func.mir_extra.append(func.gpa, @intFromEnum(opcode));
     try func.addInst(.{ .tag = .misc_prefix, .data = .{ .payload = extra_index } });
 }
 
 fn addLabel(func: *CodeGen, tag: Mir.Inst.Tag, label: u32) error{OutOfMemory}!void {
     try func.addInst(.{ .tag = tag, .data = .{ .label = label } });
 }
 
 fn addImm32(func: *CodeGen, imm: i32) error{OutOfMemory}!void {
     try func.addInst(.{ .tag = .i32_const, .data = .{ .imm32 = imm } });
 }
 
 /// Accepts an unsigned 64bit integer rather than a signed integer to
 /// prevent us from having to bitcast multiple times as most values
 /// within codegen are represented as unsigned rather than signed.
 fn addImm64(func: *CodeGen, imm: u64) error{OutOfMemory}!void {
     const extra_index = try func.addExtra(Mir.Imm64.fromU64(imm));
     try func.addInst(.{ .tag = .i64_const, .data = .{ .payload = extra_index } });
 }
 
 /// Accepts the index into the list of 128bit-immediates
 fn addImm128(func: *CodeGen, index: u32) error{OutOfMemory}!void {
     const simd_values = func.simd_immediates.items[index];
     const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
     // tag + 128bit value
     try func.mir_extra.ensureUnusedCapacity(func.gpa, 5);
     func.mir_extra.appendAssumeCapacity(std.wasm.simdOpcode(.v128_const));
     func.mir_extra.appendSliceAssumeCapacity(@alignCast(mem.bytesAsSlice(u32, &simd_values)));
     try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
 }
 
 fn addFloat64(func: *CodeGen, float: f64) error{OutOfMemory}!void {
     const extra_index = try func.addExtra(Mir.Float64.fromFloat64(float));
     try func.addInst(.{ .tag = .f64_const, .data = .{ .payload = extra_index } });
 }
 
 /// Inserts an instruction to load/store from/to wasm's linear memory dependent on the given `tag`.
 fn addMemArg(func: *CodeGen, tag: Mir.Inst.Tag, mem_arg: Mir.MemArg) error{OutOfMemory}!void {
     const extra_index = try func.addExtra(mem_arg);
     try func.addInst(.{ .tag = tag, .data = .{ .payload = extra_index } });
 }
 
 /// Inserts an instruction from the 'atomics' feature which accesses wasm's linear memory dependent on the
 /// given `tag`.
 fn addAtomicMemArg(func: *CodeGen, tag: wasm.AtomicsOpcode, mem_arg: Mir.MemArg) error{OutOfMemory}!void {
     const extra_index = try func.addExtra(@as(struct { val: u32 }, .{ .val = wasm.atomicsOpcode(tag) }));
     _ = try func.addExtra(mem_arg);
     try func.addInst(.{ .tag = .atomics_prefix, .data = .{ .payload = extra_index } });
 }
 
 /// Helper function to emit atomic mir opcodes.
 fn addAtomicTag(func: *CodeGen, tag: wasm.AtomicsOpcode) error{OutOfMemory}!void {
     const extra_index = try func.addExtra(@as(struct { val: u32 }, .{ .val = wasm.atomicsOpcode(tag) }));
     try func.addInst(.{ .tag = .atomics_prefix, .data = .{ .payload = extra_index } });
 }
 
 /// Appends entries to `mir_extra` based on the type of `extra`.
 /// Returns the index into `mir_extra`
 fn addExtra(func: *CodeGen, extra: anytype) error{OutOfMemory}!u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     try func.mir_extra.ensureUnusedCapacity(func.gpa, fields.len);
     return func.addExtraAssumeCapacity(extra);
 }
 
 /// Appends entries to `mir_extra` based on the type of `extra`.
 /// Returns the index into `mir_extra`
 fn addExtraAssumeCapacity(func: *CodeGen, extra: anytype) error{OutOfMemory}!u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     const result = @as(u32, @intCast(func.mir_extra.items.len));
     inline for (fields) |field| {
         func.mir_extra.appendAssumeCapacity(switch (field.type) {
             u32 => @field(extra, field.name),
             else => |field_type| @compileError("Unsupported field type " ++ @typeName(field_type)),
         });
     }
     return result;
 }
 
 /// Using a given `Type`, returns the corresponding type
 fn typeToValtype(ty: Type, mod: *Module) wasm.Valtype {
     const target = mod.getTarget();
     const ip = &mod.intern_pool;
     return switch (ty.zigTypeTag(mod)) {
         .Float => switch (ty.floatBits(target)) {
             16 => wasm.Valtype.i32, // stored/loaded as u16
             32 => wasm.Valtype.f32,
             64 => wasm.Valtype.f64,
             80, 128 => wasm.Valtype.i64,
             else => unreachable,
         },
         .Int, .Enum => blk: {
             const info = ty.intInfo(mod);
             if (info.bits <= 32) break :blk wasm.Valtype.i32;
             if (info.bits > 32 and info.bits <= 128) break :blk wasm.Valtype.i64;
             break :blk wasm.Valtype.i32; // represented as pointer to stack
         },
         .Struct => {
             if (mod.typeToPackedStruct(ty)) |packed_struct| {
                 return typeToValtype(Type.fromInterned(packed_struct.backingIntType(ip).*), mod);
             } else {
                 return wasm.Valtype.i32;
             }
         },
         .Vector => switch (determineSimdStoreStrategy(ty, mod)) {
             .direct => wasm.Valtype.v128,
             .unrolled => wasm.Valtype.i32,
         },
         .Union => switch (ty.containerLayout(mod)) {
             .Packed => {
                 const int_ty = mod.intType(.unsigned, @as(u16, @intCast(ty.bitSize(mod)))) catch @panic("out of memory");
                 return typeToValtype(int_ty, mod);
             },
             else => wasm.Valtype.i32,
         },
         else => wasm.Valtype.i32, // all represented as reference/immediate
     };
 }
 
 /// Using a given `Type`, returns the byte representation of its wasm value type
 fn genValtype(ty: Type, mod: *Module) u8 {
     return wasm.valtype(typeToValtype(ty, mod));
 }
 
 /// Using a given `Type`, returns the corresponding wasm value type
 /// Differently from `genValtype` this also allows `void` to create a block
 /// with no return type
 fn genBlockType(ty: Type, mod: *Module) u8 {
     return switch (ty.ip_index) {
         .void_type, .noreturn_type => wasm.block_empty,
         else => genValtype(ty, mod),
     };
 }
 
 /// Writes the bytecode depending on the given `WValue` in `val`
 fn emitWValue(func: *CodeGen, value: WValue) InnerError!void {
     switch (value) {
         .dead => unreachable, // reference to free'd `WValue` (missing reuseOperand?)
         .none, .stack => {}, // no-op
         .local => |idx| try func.addLabel(.local_get, idx.value),
         .imm32 => |val| try func.addImm32(@as(i32, @bitCast(val))),
         .imm64 => |val| try func.addImm64(val),
         .imm128 => |val| try func.addImm128(val),
         .float32 => |val| try func.addInst(.{ .tag = .f32_const, .data = .{ .float32 = val } }),
         .float64 => |val| try func.addFloat64(val),
         .memory => |ptr| {
             const extra_index = try func.addExtra(Mir.Memory{ .pointer = ptr, .offset = 0 });
             try func.addInst(.{ .tag = .memory_address, .data = .{ .payload = extra_index } });
         },
         .memory_offset => |mem_off| {
             const extra_index = try func.addExtra(Mir.Memory{ .pointer = mem_off.pointer, .offset = mem_off.offset });
             try func.addInst(.{ .tag = .memory_address, .data = .{ .payload = extra_index } });
         },
         .function_index => |index| try func.addLabel(.function_index, index), // write function index and generate relocation
         .stack_offset => try func.addLabel(.local_get, func.bottom_stack_value.local.value), // caller must ensure to address the offset
     }
 }
 
 /// If given a local or stack-offset, increases the reference count by 1.
 /// The old `WValue` found at instruction `ref` is then replaced by the
 /// modified `WValue` and returned. When given a non-local or non-stack-offset,
 /// returns the given `operand` itfunc instead.
 fn reuseOperand(func: *CodeGen, ref: Air.Inst.Ref, operand: WValue) WValue {
     if (operand != .local and operand != .stack_offset) return operand;
     var new_value = operand;
     switch (new_value) {
         .local => |*local| local.references += 1,
         .stack_offset => |*stack_offset| stack_offset.references += 1,
         else => unreachable,
     }
     const old_value = func.getResolvedInst(ref);
     old_value.* = new_value;
     return new_value;
 }
 
 /// From a reference, returns its resolved `WValue`.
 /// It's illegal to provide a `Air.Inst.Ref` that hasn't been resolved yet.
 fn getResolvedInst(func: *CodeGen, ref: Air.Inst.Ref) *WValue {
     var index = func.branches.items.len;
     while (index > 0) : (index -= 1) {
         const branch = func.branches.items[index - 1];
         if (branch.values.getPtr(ref)) |value| {
             return value;
         }
     }
     unreachable; // developer-error: This can only be called on resolved instructions. Use `resolveInst` instead.
 }
 
 /// Creates one locals for a given `Type`.
 /// Returns a corresponding `Wvalue` with `local` as active tag
 fn allocLocal(func: *CodeGen, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const valtype = typeToValtype(ty, mod);
     switch (valtype) {
         .i32 => if (func.free_locals_i32.popOrNull()) |index| {
             log.debug("reusing local ({d}) of type {}", .{ index, valtype });
             return WValue{ .local = .{ .value = index, .references = 1 } };
         },
         .i64 => if (func.free_locals_i64.popOrNull()) |index| {
             log.debug("reusing local ({d}) of type {}", .{ index, valtype });
             return WValue{ .local = .{ .value = index, .references = 1 } };
         },
         .f32 => if (func.free_locals_f32.popOrNull()) |index| {
             log.debug("reusing local ({d}) of type {}", .{ index, valtype });
             return WValue{ .local = .{ .value = index, .references = 1 } };
         },
         .f64 => if (func.free_locals_f64.popOrNull()) |index| {
             log.debug("reusing local ({d}) of type {}", .{ index, valtype });
             return WValue{ .local = .{ .value = index, .references = 1 } };
         },
         .v128 => if (func.free_locals_v128.popOrNull()) |index| {
             log.debug("reusing local ({d}) of type {}", .{ index, valtype });
             return WValue{ .local = .{ .value = index, .references = 1 } };
         },
     }
     log.debug("new local of type {}", .{valtype});
     // no local was free to be re-used, so allocate a new local instead
     return func.ensureAllocLocal(ty);
 }
 
 /// Ensures a new local will be created. This is useful when it's useful
 /// to use a zero-initialized local.
 fn ensureAllocLocal(func: *CodeGen, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     try func.locals.append(func.gpa, genValtype(ty, mod));
     const initial_index = func.local_index;
     func.local_index += 1;
     return WValue{ .local = .{ .value = initial_index, .references = 1 } };
 }
 
 /// Generates a `wasm.Type` from a given function type.
 /// Memory is owned by the caller.
 fn genFunctype(
     gpa: Allocator,
     cc: std.builtin.CallingConvention,
     params: []const InternPool.Index,
     return_type: Type,
     mod: *Module,
 ) !wasm.Type {
     var temp_params = std.ArrayList(wasm.Valtype).init(gpa);
     defer temp_params.deinit();
     var returns = std.ArrayList(wasm.Valtype).init(gpa);
     defer returns.deinit();
 
     if (firstParamSRet(cc, return_type, mod)) {
         try temp_params.append(.i32); // memory address is always a 32-bit handle
     } else if (return_type.hasRuntimeBitsIgnoreComptime(mod)) {
         if (cc == .C) {
             const res_classes = abi.classifyType(return_type, mod);
             assert(res_classes[0] == .direct and res_classes[1] == .none);
             const scalar_type = abi.scalarType(return_type, mod);
             try returns.append(typeToValtype(scalar_type, mod));
         } else {
             try returns.append(typeToValtype(return_type, mod));
         }
     } else if (return_type.isError(mod)) {
         try returns.append(.i32);
     }
 
     // param types
     for (params) |param_type_ip| {
         const param_type = Type.fromInterned(param_type_ip);
         if (!param_type.hasRuntimeBitsIgnoreComptime(mod)) continue;
 
         switch (cc) {
             .C => {
                 const param_classes = abi.classifyType(param_type, mod);
                 for (param_classes) |class| {
                     if (class == .none) continue;
                     if (class == .direct) {
                         const scalar_type = abi.scalarType(param_type, mod);
                         try temp_params.append(typeToValtype(scalar_type, mod));
                     } else {
                         try temp_params.append(typeToValtype(param_type, mod));
                     }
                 }
             },
             else => if (isByRef(param_type, mod))
                 try temp_params.append(.i32)
             else
                 try temp_params.append(typeToValtype(param_type, mod)),
         }
     }
 
     return wasm.Type{
         .params = try temp_params.toOwnedSlice(),
         .returns = try returns.toOwnedSlice(),
     };
 }
 
 pub fn generate(
     bin_file: *link.File,
     src_loc: Module.SrcLoc,
     func_index: InternPool.Index,
     air: Air,
     liveness: Liveness,
     code: *std.ArrayList(u8),
     debug_output: codegen.DebugInfoOutput,
 ) codegen.CodeGenError!codegen.Result {
     _ = src_loc;
     const mod = bin_file.options.module.?;
     const func = mod.funcInfo(func_index);
     var code_gen: CodeGen = .{
         .gpa = bin_file.allocator,
         .air = air,
         .liveness = liveness,
         .code = code,
         .decl_index = func.owner_decl,
         .decl = mod.declPtr(func.owner_decl),
         .err_msg = undefined,
         .locals = .{},
         .target = bin_file.options.target,
         .bin_file = bin_file.cast(link.File.Wasm).?,
         .debug_output = debug_output,
         .func_index = func_index,
     };
     defer code_gen.deinit();
 
     genFunc(&code_gen) catch |err| switch (err) {
         error.CodegenFail => return codegen.Result{ .fail = code_gen.err_msg },
         else => |e| return e,
     };
 
     return codegen.Result.ok;
 }
 
 fn genFunc(func: *CodeGen) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const fn_info = mod.typeToFunc(func.decl.ty).?;
     var func_type = try genFunctype(func.gpa, fn_info.cc, fn_info.param_types.get(ip), Type.fromInterned(fn_info.return_type), mod);
     defer func_type.deinit(func.gpa);
     _ = try func.bin_file.storeDeclType(func.decl_index, func_type);
 
     var cc_result = try func.resolveCallingConventionValues(func.decl.ty);
     defer cc_result.deinit(func.gpa);
 
     func.args = cc_result.args;
     func.return_value = cc_result.return_value;
 
     try func.addTag(.dbg_prologue_end);
 
     try func.branches.append(func.gpa, .{});
     // clean up outer branch
     defer {
         var outer_branch = func.branches.pop();
         outer_branch.deinit(func.gpa);
         assert(func.branches.items.len == 0); // missing branch merge
     }
     // Generate MIR for function body
     try func.genBody(func.air.getMainBody());
 
     // In case we have a return value, but the last instruction is a noreturn (such as a while loop)
     // we emit an unreachable instruction to tell the stack validator that part will never be reached.
     if (func_type.returns.len != 0 and func.air.instructions.len > 0) {
         const inst: Air.Inst.Index = @enumFromInt(func.air.instructions.len - 1);
         const last_inst_ty = func.typeOfIndex(inst);
         if (!last_inst_ty.hasRuntimeBitsIgnoreComptime(mod) or last_inst_ty.isNoReturn(mod)) {
             try func.addTag(.@"unreachable");
         }
     }
     // End of function body
     try func.addTag(.end);
 
     try func.addTag(.dbg_epilogue_begin);
 
     // check if we have to initialize and allocate anything into the stack frame.
     // If so, create enough stack space and insert the instructions at the front of the list.
     if (func.initial_stack_value != .none) {
         var prologue = std.ArrayList(Mir.Inst).init(func.gpa);
         defer prologue.deinit();
 
         // load stack pointer
         try prologue.append(.{ .tag = .global_get, .data = .{ .label = 0 } });
         // store stack pointer so we can restore it when we return from the function
         try prologue.append(.{ .tag = .local_tee, .data = .{ .label = func.initial_stack_value.local.value } });
         // get the total stack size
         const aligned_stack = func.stack_alignment.forward(func.stack_size);
         try prologue.append(.{ .tag = .i32_const, .data = .{ .imm32 = @intCast(aligned_stack) } });
         // subtract it from the current stack pointer
         try prologue.append(.{ .tag = .i32_sub, .data = .{ .tag = {} } });
         // Get negative stack aligment
         try prologue.append(.{ .tag = .i32_const, .data = .{ .imm32 = @as(i32, @intCast(func.stack_alignment.toByteUnitsOptional().?)) * -1 } });
         // Bitwise-and the value to get the new stack pointer to ensure the pointers are aligned with the abi alignment
         try prologue.append(.{ .tag = .i32_and, .data = .{ .tag = {} } });
         // store the current stack pointer as the bottom, which will be used to calculate all stack pointer offsets
         try prologue.append(.{ .tag = .local_tee, .data = .{ .label = func.bottom_stack_value.local.value } });
         // Store the current stack pointer value into the global stack pointer so other function calls will
         // start from this value instead and not overwrite the current stack.
         try prologue.append(.{ .tag = .global_set, .data = .{ .label = 0 } });
 
         // reserve space and insert all prologue instructions at the front of the instruction list
         // We insert them in reserve order as there is no insertSlice in multiArrayList.
         try func.mir_instructions.ensureUnusedCapacity(func.gpa, prologue.items.len);
         for (prologue.items, 0..) |_, index| {
             const inst = prologue.items[prologue.items.len - 1 - index];
             func.mir_instructions.insertAssumeCapacity(0, inst);
         }
     }
 
     var mir: Mir = .{
         .instructions = func.mir_instructions.toOwnedSlice(),
         .extra = try func.mir_extra.toOwnedSlice(func.gpa),
     };
     defer mir.deinit(func.gpa);
 
     var emit: Emit = .{
         .mir = mir,
         .bin_file = func.bin_file,
         .code = func.code,
         .locals = func.locals.items,
         .decl_index = func.decl_index,
         .dbg_output = func.debug_output,
         .prev_di_line = 0,
         .prev_di_column = 0,
         .prev_di_offset = 0,
     };
 
     emit.emitMir() catch |err| switch (err) {
         error.EmitFail => {
             func.err_msg = emit.error_msg.?;
             return error.CodegenFail;
         },
         else => |e| return e,
     };
 }
 
 const CallWValues = struct {
     args: []WValue,
     return_value: WValue,
 
     fn deinit(values: *CallWValues, gpa: Allocator) void {
         gpa.free(values.args);
         values.* = undefined;
     }
 };
 
 fn resolveCallingConventionValues(func: *CodeGen, fn_ty: Type) InnerError!CallWValues {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const fn_info = mod.typeToFunc(fn_ty).?;
     const cc = fn_info.cc;
     var result: CallWValues = .{
         .args = &.{},
         .return_value = .none,
     };
     if (cc == .Naked) return result;
 
     var args = std.ArrayList(WValue).init(func.gpa);
     defer args.deinit();
 
     // Check if we store the result as a pointer to the stack rather than
     // by value
     if (firstParamSRet(fn_info.cc, Type.fromInterned(fn_info.return_type), mod)) {
         // the sret arg will be passed as first argument, therefore we
         // set the `return_value` before allocating locals for regular args.
         result.return_value = .{ .local = .{ .value = func.local_index, .references = 1 } };
         func.local_index += 1;
     }
 
     switch (cc) {
         .Unspecified => {
             for (fn_info.param_types.get(ip)) |ty| {
                 if (!Type.fromInterned(ty).hasRuntimeBitsIgnoreComptime(mod)) {
                     continue;
                 }
 
                 try args.append(.{ .local = .{ .value = func.local_index, .references = 1 } });
                 func.local_index += 1;
             }
         },
         .C => {
             for (fn_info.param_types.get(ip)) |ty| {
                 const ty_classes = abi.classifyType(Type.fromInterned(ty), mod);
                 for (ty_classes) |class| {
                     if (class == .none) continue;
                     try args.append(.{ .local = .{ .value = func.local_index, .references = 1 } });
                     func.local_index += 1;
                 }
             }
         },
         else => return func.fail("calling convention '{s}' not supported for Wasm", .{@tagName(cc)}),
     }
     result.args = try args.toOwnedSlice();
     return result;
 }
 
 fn firstParamSRet(cc: std.builtin.CallingConvention, return_type: Type, mod: *Module) bool {
     switch (cc) {
         .Unspecified, .Inline => return isByRef(return_type, mod),
         .C => {
             const ty_classes = abi.classifyType(return_type, mod);
             if (ty_classes[0] == .indirect) return true;
             if (ty_classes[0] == .direct and ty_classes[1] == .direct) return true;
             return false;
         },
         else => return false,
     }
 }
 
 /// Lowers a Zig type and its value based on a given calling convention to ensure
 /// it matches the ABI.
 fn lowerArg(func: *CodeGen, cc: std.builtin.CallingConvention, ty: Type, value: WValue) !void {
     if (cc != .C) {
         return func.lowerToStack(value);
     }
 
     const mod = func.bin_file.base.comp.module.?;
     const ty_classes = abi.classifyType(ty, mod);
     assert(ty_classes[0] != .none);
     switch (ty.zigTypeTag(mod)) {
         .Struct, .Union => {
             if (ty_classes[0] == .indirect) {
                 return func.lowerToStack(value);
             }
             assert(ty_classes[0] == .direct);
             const scalar_type = abi.scalarType(ty, mod);
             const abi_size = scalar_type.abiSize(mod);
             try func.emitWValue(value);
 
             // When the value lives in the virtual stack, we must load it onto the actual stack
             if (value != .imm32 and value != .imm64) {
                 const opcode = buildOpcode(.{
                     .op = .load,
                     .width = @as(u8, @intCast(abi_size)),
                     .signedness = if (scalar_type.isSignedInt(mod)) .signed else .unsigned,
                     .valtype1 = typeToValtype(scalar_type, mod),
                 });
                 try func.addMemArg(Mir.Inst.Tag.fromOpcode(opcode), .{
                     .offset = value.offset(),
                     .alignment = @intCast(scalar_type.abiAlignment(mod).toByteUnitsOptional().?),
                 });
             }
         },
         .Int, .Float => {
             if (ty_classes[1] == .none) {
                 return func.lowerToStack(value);
             }
             assert(ty_classes[0] == .direct and ty_classes[1] == .direct);
             assert(ty.abiSize(mod) == 16);
             // in this case we have an integer or float that must be lowered as 2 i64's.
             try func.emitWValue(value);
             try func.addMemArg(.i64_load, .{ .offset = value.offset(), .alignment = 8 });
             try func.emitWValue(value);
             try func.addMemArg(.i64_load, .{ .offset = value.offset() + 8, .alignment = 8 });
         },
         else => return func.lowerToStack(value),
     }
 }
 
 /// Lowers a `WValue` to the stack. This means when the `value` results in
 /// `.stack_offset` we calculate the pointer of this offset and use that.
 /// The value is left on the stack, and not stored in any temporary.
 fn lowerToStack(func: *CodeGen, value: WValue) !void {
     switch (value) {
         .stack_offset => |offset| {
             try func.emitWValue(value);
             if (offset.value > 0) {
                 switch (func.arch()) {
                     .wasm32 => {
                         try func.addImm32(@as(i32, @bitCast(offset.value)));
                         try func.addTag(.i32_add);
                     },
                     .wasm64 => {
                         try func.addImm64(offset.value);
                         try func.addTag(.i64_add);
                     },
                     else => unreachable,
                 }
             }
         },
         else => try func.emitWValue(value),
     }
 }
 
 /// Creates a local for the initial stack value
 /// Asserts `initial_stack_value` is `.none`
 fn initializeStack(func: *CodeGen) !void {
     assert(func.initial_stack_value == .none);
     // Reserve a local to store the current stack pointer
     // We can later use this local to set the stack pointer back to the value
     // we have stored here.
     func.initial_stack_value = try func.ensureAllocLocal(Type.usize);
     // Also reserve a local to store the bottom stack value
     func.bottom_stack_value = try func.ensureAllocLocal(Type.usize);
 }
 
 /// Reads the stack pointer from `Context.initial_stack_value` and writes it
 /// to the global stack pointer variable
 fn restoreStackPointer(func: *CodeGen) !void {
     // only restore the pointer if it was initialized
     if (func.initial_stack_value == .none) return;
     // Get the original stack pointer's value
     try func.emitWValue(func.initial_stack_value);
 
     // save its value in the global stack pointer
     try func.addLabel(.global_set, 0);
 }
 
 /// From a given type, will create space on the virtual stack to store the value of such type.
 /// This returns a `WValue` with its active tag set to `local`, containing the index to the local
 /// that points to the position on the virtual stack. This function should be used instead of
 /// moveStack unless a local was already created to store the pointer.
 ///
 /// Asserts Type has codegenbits
 fn allocStack(func: *CodeGen, ty: Type) !WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(ty.hasRuntimeBitsIgnoreComptime(mod));
     if (func.initial_stack_value == .none) {
         try func.initializeStack();
     }
 
     const abi_size = std.math.cast(u32, ty.abiSize(mod)) orelse {
         return func.fail("Type {} with ABI size of {d} exceeds stack frame size", .{
             ty.fmt(mod), ty.abiSize(mod),
         });
     };
     const abi_align = ty.abiAlignment(mod);
 
     func.stack_alignment = func.stack_alignment.max(abi_align);
 
     const offset: u32 = @intCast(abi_align.forward(func.stack_size));
     defer func.stack_size = offset + abi_size;
 
     return WValue{ .stack_offset = .{ .value = offset, .references = 1 } };
 }
 
 /// From a given AIR instruction generates a pointer to the stack where
 /// the value of its type will live.
 /// This is different from allocStack where this will use the pointer's alignment
 /// if it is set, to ensure the stack alignment will be set correctly.
 fn allocStackPtr(func: *CodeGen, inst: Air.Inst.Index) !WValue {
     const mod = func.bin_file.base.comp.module.?;
     const ptr_ty = func.typeOfIndex(inst);
     const pointee_ty = ptr_ty.childType(mod);
 
     if (func.initial_stack_value == .none) {
         try func.initializeStack();
     }
 
     if (!pointee_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         return func.allocStack(Type.usize); // create a value containing just the stack pointer.
     }
 
     const abi_alignment = ptr_ty.ptrAlignment(mod);
     const abi_size = std.math.cast(u32, pointee_ty.abiSize(mod)) orelse {
         return func.fail("Type {} with ABI size of {d} exceeds stack frame size", .{
             pointee_ty.fmt(mod), pointee_ty.abiSize(mod),
         });
     };
     func.stack_alignment = func.stack_alignment.max(abi_alignment);
 
     const offset: u32 = @intCast(abi_alignment.forward(func.stack_size));
     defer func.stack_size = offset + abi_size;
 
     return WValue{ .stack_offset = .{ .value = offset, .references = 1 } };
 }
 
 /// From given zig bitsize, returns the wasm bitsize
 fn toWasmBits(bits: u16) ?u16 {
     return for ([_]u16{ 32, 64, 128 }) |wasm_bits| {
         if (bits <= wasm_bits) return wasm_bits;
     } else null;
 }
 
 /// Performs a copy of bytes for a given type. Copying all bytes
 /// from rhs to lhs.
 fn memcpy(func: *CodeGen, dst: WValue, src: WValue, len: WValue) !void {
     // When bulk_memory is enabled, we lower it to wasm's memcpy instruction.
     // If not, we lower it ourselves manually
     if (std.Target.wasm.featureSetHas(func.target.cpu.features, .bulk_memory)) {
         try func.lowerToStack(dst);
         try func.lowerToStack(src);
         try func.emitWValue(len);
         try func.addExtended(.memory_copy);
         return;
     }
 
     // when the length is comptime-known, rather than a runtime value, we can optimize the generated code by having
     // the loop during codegen, rather than inserting a runtime loop into the binary.
     switch (len) {
         .imm32, .imm64 => blk: {
             const length = switch (len) {
                 .imm32 => |val| val,
                 .imm64 => |val| val,
                 else => unreachable,
             };
             // if the size (length) is more than 32 bytes, we use a runtime loop instead to prevent
             // binary size bloat.
             if (length > 32) break :blk;
             var offset: u32 = 0;
             const lhs_base = dst.offset();
             const rhs_base = src.offset();
             while (offset < length) : (offset += 1) {
                 // get dst's address to store the result
                 try func.emitWValue(dst);
                 // load byte from src's address
                 try func.emitWValue(src);
                 switch (func.arch()) {
                     .wasm32 => {
                         try func.addMemArg(.i32_load8_u, .{ .offset = rhs_base + offset, .alignment = 1 });
                         try func.addMemArg(.i32_store8, .{ .offset = lhs_base + offset, .alignment = 1 });
                     },
                     .wasm64 => {
                         try func.addMemArg(.i64_load8_u, .{ .offset = rhs_base + offset, .alignment = 1 });
                         try func.addMemArg(.i64_store8, .{ .offset = lhs_base + offset, .alignment = 1 });
                     },
                     else => unreachable,
                 }
             }
             return;
         },
         else => {},
     }
 
     // allocate a local for the offset, and set it to 0.
     // This to ensure that inside loops we correctly re-set the counter.
     var offset = try func.allocLocal(Type.usize); // local for counter
     defer offset.free(func);
     switch (func.arch()) {
         .wasm32 => try func.addImm32(0),
         .wasm64 => try func.addImm64(0),
         else => unreachable,
     }
     try func.addLabel(.local_set, offset.local.value);
 
     // outer block to jump to when loop is done
     try func.startBlock(.block, wasm.block_empty);
     try func.startBlock(.loop, wasm.block_empty);
 
     // loop condition (offset == length -> break)
     {
         try func.emitWValue(offset);
         try func.emitWValue(len);
         switch (func.arch()) {
             .wasm32 => try func.addTag(.i32_eq),
             .wasm64 => try func.addTag(.i64_eq),
             else => unreachable,
         }
         try func.addLabel(.br_if, 1); // jump out of loop into outer block (finished)
     }
 
     // get dst ptr
     {
         try func.emitWValue(dst);
         try func.emitWValue(offset);
         switch (func.arch()) {
             .wasm32 => try func.addTag(.i32_add),
             .wasm64 => try func.addTag(.i64_add),
             else => unreachable,
         }
     }
 
     // get src value and also store in dst
     {
         try func.emitWValue(src);
         try func.emitWValue(offset);
         switch (func.arch()) {
             .wasm32 => {
                 try func.addTag(.i32_add);
                 try func.addMemArg(.i32_load8_u, .{ .offset = src.offset(), .alignment = 1 });
                 try func.addMemArg(.i32_store8, .{ .offset = dst.offset(), .alignment = 1 });
             },
             .wasm64 => {
                 try func.addTag(.i64_add);
                 try func.addMemArg(.i64_load8_u, .{ .offset = src.offset(), .alignment = 1 });
                 try func.addMemArg(.i64_store8, .{ .offset = dst.offset(), .alignment = 1 });
             },
             else => unreachable,
         }
     }
 
     // increment loop counter
     {
         try func.emitWValue(offset);
         switch (func.arch()) {
             .wasm32 => {
                 try func.addImm32(1);
                 try func.addTag(.i32_add);
             },
             .wasm64 => {
                 try func.addImm64(1);
                 try func.addTag(.i64_add);
             },
             else => unreachable,
         }
         try func.addLabel(.local_set, offset.local.value);
         try func.addLabel(.br, 0); // jump to start of loop
     }
     try func.endBlock(); // close off loop block
     try func.endBlock(); // close off outer block
 }
 
 fn ptrSize(func: *const CodeGen) u16 {
     return @divExact(func.target.ptrBitWidth(), 8);
 }
 
 fn arch(func: *const CodeGen) std.Target.Cpu.Arch {
     return func.target.cpu.arch;
 }
 
 /// For a given `Type`, will return true when the type will be passed
 /// by reference, rather than by value
 fn isByRef(ty: Type, mod: *Module) bool {
     const ip = &mod.intern_pool;
     const target = mod.getTarget();
     switch (ty.zigTypeTag(mod)) {
         .Type,
         .ComptimeInt,
         .ComptimeFloat,
         .EnumLiteral,
         .Undefined,
         .Null,
         .Opaque,
         => unreachable,
 
         .NoReturn,
         .Void,
         .Bool,
         .ErrorSet,
         .Fn,
         .Enum,
         .AnyFrame,
         => return false,
 
         .Array,
         .Frame,
         => return ty.hasRuntimeBitsIgnoreComptime(mod),
         .Union => {
             if (mod.typeToUnion(ty)) |union_obj| {
                 if (union_obj.getLayout(ip) == .Packed) {
                     return ty.abiSize(mod) > 8;
                 }
             }
             return ty.hasRuntimeBitsIgnoreComptime(mod);
         },
         .Struct => {
             if (mod.typeToPackedStruct(ty)) |packed_struct| {
                 return isByRef(Type.fromInterned(packed_struct.backingIntType(ip).*), mod);
             }
             return ty.hasRuntimeBitsIgnoreComptime(mod);
         },
         .Vector => return determineSimdStoreStrategy(ty, mod) == .unrolled,
         .Int => return ty.intInfo(mod).bits > 64,
         .Float => return ty.floatBits(target) > 64,
         .ErrorUnion => {
             const pl_ty = ty.errorUnionPayload(mod);
             if (!pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
                 return false;
             }
             return true;
         },
         .Optional => {
             if (ty.isPtrLikeOptional(mod)) return false;
             const pl_type = ty.optionalChild(mod);
             if (pl_type.zigTypeTag(mod) == .ErrorSet) return false;
             return pl_type.hasRuntimeBitsIgnoreComptime(mod);
         },
         .Pointer => {
             // Slices act like struct and will be passed by reference
             if (ty.isSlice(mod)) return true;
             return false;
         },
     }
 }
 
 const SimdStoreStrategy = enum {
     direct,
     unrolled,
 };
 
 /// For a given vector type, returns the `SimdStoreStrategy`.
 /// This means when a given type is 128 bits and either the simd128 or relaxed-simd
 /// features are enabled, the function will return `.direct`. This would allow to store
 /// it using a instruction, rather than an unrolled version.
 fn determineSimdStoreStrategy(ty: Type, mod: *Module) SimdStoreStrategy {
     std.debug.assert(ty.zigTypeTag(mod) == .Vector);
     if (ty.bitSize(mod) != 128) return .unrolled;
     const hasFeature = std.Target.wasm.featureSetHas;
     const target = mod.getTarget();
     const features = target.cpu.features;
     if (hasFeature(features, .relaxed_simd) or hasFeature(features, .simd128)) {
         return .direct;
     }
     return .unrolled;
 }
 
 /// Creates a new local for a pointer that points to memory with given offset.
 /// This can be used to get a pointer to a struct field, error payload, etc.
 /// By providing `modify` as action, it will modify the given `ptr_value` instead of making a new
 /// local value to store the pointer. This allows for local re-use and improves binary size.
 fn buildPointerOffset(func: *CodeGen, ptr_value: WValue, offset: u64, action: enum { modify, new }) InnerError!WValue {
     // do not perform arithmetic when offset is 0.
     if (offset == 0 and ptr_value.offset() == 0 and action == .modify) return ptr_value;
     const result_ptr: WValue = switch (action) {
         .new => try func.ensureAllocLocal(Type.usize),
         .modify => ptr_value,
     };
     try func.emitWValue(ptr_value);
     if (offset + ptr_value.offset() > 0) {
         switch (func.arch()) {
             .wasm32 => {
                 try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(offset + ptr_value.offset())))));
                 try func.addTag(.i32_add);
             },
             .wasm64 => {
                 try func.addImm64(offset + ptr_value.offset());
                 try func.addTag(.i64_add);
             },
             else => unreachable,
         }
     }
     try func.addLabel(.local_set, result_ptr.local.value);
     return result_ptr;
 }
 
 fn genInst(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const air_tags = func.air.instructions.items(.tag);
     return switch (air_tags[@intFromEnum(inst)]) {
         .inferred_alloc, .inferred_alloc_comptime => unreachable,
 
         .add => func.airBinOp(inst, .add),
         .add_sat => func.airSatBinOp(inst, .add),
         .add_wrap => func.airWrapBinOp(inst, .add),
         .sub => func.airBinOp(inst, .sub),
         .sub_sat => func.airSatBinOp(inst, .sub),
         .sub_wrap => func.airWrapBinOp(inst, .sub),
         .mul => func.airBinOp(inst, .mul),
         .mul_wrap => func.airWrapBinOp(inst, .mul),
         .div_float, .div_exact => func.airDiv(inst),
         .div_trunc => func.airDivTrunc(inst),
         .div_floor => func.airDivFloor(inst),
         .bit_and => func.airBinOp(inst, .@"and"),
         .bit_or => func.airBinOp(inst, .@"or"),
         .bool_and => func.airBinOp(inst, .@"and"),
         .bool_or => func.airBinOp(inst, .@"or"),
         .rem => func.airBinOp(inst, .rem),
         .mod => func.airMod(inst),
         .shl => func.airWrapBinOp(inst, .shl),
         .shl_exact => func.airBinOp(inst, .shl),
         .shl_sat => func.airShlSat(inst),
         .shr, .shr_exact => func.airBinOp(inst, .shr),
         .xor => func.airBinOp(inst, .xor),
         .max => func.airMaxMin(inst, .max),
         .min => func.airMaxMin(inst, .min),
         .mul_add => func.airMulAdd(inst),
 
         .sqrt => func.airUnaryFloatOp(inst, .sqrt),
         .sin => func.airUnaryFloatOp(inst, .sin),
         .cos => func.airUnaryFloatOp(inst, .cos),
         .tan => func.airUnaryFloatOp(inst, .tan),
         .exp => func.airUnaryFloatOp(inst, .exp),
         .exp2 => func.airUnaryFloatOp(inst, .exp2),
         .log => func.airUnaryFloatOp(inst, .log),
         .log2 => func.airUnaryFloatOp(inst, .log2),
         .log10 => func.airUnaryFloatOp(inst, .log10),
         .floor => func.airUnaryFloatOp(inst, .floor),
         .ceil => func.airUnaryFloatOp(inst, .ceil),
         .round => func.airUnaryFloatOp(inst, .round),
         .trunc_float => func.airUnaryFloatOp(inst, .trunc),
         .neg => func.airUnaryFloatOp(inst, .neg),
 
         .abs => func.airAbs(inst),
 
         .add_with_overflow => func.airAddSubWithOverflow(inst, .add),
         .sub_with_overflow => func.airAddSubWithOverflow(inst, .sub),
         .shl_with_overflow => func.airShlWithOverflow(inst),
         .mul_with_overflow => func.airMulWithOverflow(inst),
 
         .clz => func.airClz(inst),
         .ctz => func.airCtz(inst),
 
         .cmp_eq => func.airCmp(inst, .eq),
         .cmp_gte => func.airCmp(inst, .gte),
         .cmp_gt => func.airCmp(inst, .gt),
         .cmp_lte => func.airCmp(inst, .lte),
         .cmp_lt => func.airCmp(inst, .lt),
         .cmp_neq => func.airCmp(inst, .neq),
 
         .cmp_vector => func.airCmpVector(inst),
         .cmp_lt_errors_len => func.airCmpLtErrorsLen(inst),
 
         .array_elem_val => func.airArrayElemVal(inst),
         .array_to_slice => func.airArrayToSlice(inst),
         .alloc => func.airAlloc(inst),
         .arg => func.airArg(inst),
         .bitcast => func.airBitcast(inst),
         .block => func.airBlock(inst),
         .trap => func.airTrap(inst),
         .breakpoint => func.airBreakpoint(inst),
         .br => func.airBr(inst),
         .int_from_bool => func.airIntFromBool(inst),
         .cond_br => func.airCondBr(inst),
         .intcast => func.airIntcast(inst),
         .fptrunc => func.airFptrunc(inst),
         .fpext => func.airFpext(inst),
         .int_from_float => func.airIntFromFloat(inst),
         .float_from_int => func.airFloatFromInt(inst),
         .get_union_tag => func.airGetUnionTag(inst),
 
         .@"try" => func.airTry(inst),
         .try_ptr => func.airTryPtr(inst),
 
         // TODO
         .dbg_inline_begin,
         .dbg_inline_end,
         .dbg_block_begin,
         .dbg_block_end,
         => func.finishAir(inst, .none, &.{}),
 
         .dbg_var_ptr => func.airDbgVar(inst, true),
         .dbg_var_val => func.airDbgVar(inst, false),
 
         .dbg_stmt => func.airDbgStmt(inst),
 
         .call => func.airCall(inst, .auto),
         .call_always_tail => func.airCall(inst, .always_tail),
         .call_never_tail => func.airCall(inst, .never_tail),
         .call_never_inline => func.airCall(inst, .never_inline),
 
         .is_err => func.airIsErr(inst, .i32_ne),
         .is_non_err => func.airIsErr(inst, .i32_eq),
 
         .is_null => func.airIsNull(inst, .i32_eq, .value),
         .is_non_null => func.airIsNull(inst, .i32_ne, .value),
         .is_null_ptr => func.airIsNull(inst, .i32_eq, .ptr),
         .is_non_null_ptr => func.airIsNull(inst, .i32_ne, .ptr),
 
         .load => func.airLoad(inst),
         .loop => func.airLoop(inst),
         .memset => func.airMemset(inst, false),
         .memset_safe => func.airMemset(inst, true),
         .not => func.airNot(inst),
         .optional_payload => func.airOptionalPayload(inst),
         .optional_payload_ptr => func.airOptionalPayloadPtr(inst),
         .optional_payload_ptr_set => func.airOptionalPayloadPtrSet(inst),
         .ptr_add => func.airPtrBinOp(inst, .add),
         .ptr_sub => func.airPtrBinOp(inst, .sub),
         .ptr_elem_ptr => func.airPtrElemPtr(inst),
         .ptr_elem_val => func.airPtrElemVal(inst),
         .int_from_ptr => func.airIntFromPtr(inst),
         .ret => func.airRet(inst),
         .ret_ptr => func.airRetPtr(inst),
         .ret_load => func.airRetLoad(inst),
         .splat => func.airSplat(inst),
         .select => func.airSelect(inst),
         .shuffle => func.airShuffle(inst),
         .reduce => func.airReduce(inst),
         .aggregate_init => func.airAggregateInit(inst),
         .union_init => func.airUnionInit(inst),
         .prefetch => func.airPrefetch(inst),
         .popcount => func.airPopcount(inst),
         .byte_swap => func.airByteSwap(inst),
 
         .slice => func.airSlice(inst),
         .slice_len => func.airSliceLen(inst),
         .slice_elem_val => func.airSliceElemVal(inst),
         .slice_elem_ptr => func.airSliceElemPtr(inst),
         .slice_ptr => func.airSlicePtr(inst),
         .ptr_slice_len_ptr => func.airPtrSliceFieldPtr(inst, func.ptrSize()),
         .ptr_slice_ptr_ptr => func.airPtrSliceFieldPtr(inst, 0),
         .store => func.airStore(inst, false),
         .store_safe => func.airStore(inst, true),
 
         .set_union_tag => func.airSetUnionTag(inst),
         .struct_field_ptr => func.airStructFieldPtr(inst),
         .struct_field_ptr_index_0 => func.airStructFieldPtrIndex(inst, 0),
         .struct_field_ptr_index_1 => func.airStructFieldPtrIndex(inst, 1),
         .struct_field_ptr_index_2 => func.airStructFieldPtrIndex(inst, 2),
         .struct_field_ptr_index_3 => func.airStructFieldPtrIndex(inst, 3),
         .struct_field_val => func.airStructFieldVal(inst),
         .field_parent_ptr => func.airFieldParentPtr(inst),
 
         .switch_br => func.airSwitchBr(inst),
         .trunc => func.airTrunc(inst),
         .unreach => func.airUnreachable(inst),
 
         .wrap_optional => func.airWrapOptional(inst),
         .unwrap_errunion_payload => func.airUnwrapErrUnionPayload(inst, false),
         .unwrap_errunion_payload_ptr => func.airUnwrapErrUnionPayload(inst, true),
         .unwrap_errunion_err => func.airUnwrapErrUnionError(inst, false),
         .unwrap_errunion_err_ptr => func.airUnwrapErrUnionError(inst, true),
         .wrap_errunion_payload => func.airWrapErrUnionPayload(inst),
         .wrap_errunion_err => func.airWrapErrUnionErr(inst),
         .errunion_payload_ptr_set => func.airErrUnionPayloadPtrSet(inst),
         .error_name => func.airErrorName(inst),
 
         .wasm_memory_size => func.airWasmMemorySize(inst),
         .wasm_memory_grow => func.airWasmMemoryGrow(inst),
 
         .memcpy => func.airMemcpy(inst),
 
         .ret_addr => func.airRetAddr(inst),
         .tag_name => func.airTagName(inst),
 
         .error_set_has_value => func.airErrorSetHasValue(inst),
         .frame_addr => func.airFrameAddress(inst),
 
         .mul_sat,
         .assembly,
         .bit_reverse,
         .is_err_ptr,
         .is_non_err_ptr,
 
         .err_return_trace,
         .set_err_return_trace,
         .save_err_return_trace_index,
         .is_named_enum_value,
         .addrspace_cast,
         .vector_store_elem,
         .c_va_arg,
         .c_va_copy,
         .c_va_end,
         .c_va_start,
         => |tag| return func.fail("TODO: Implement wasm inst: {s}", .{@tagName(tag)}),
 
         .atomic_load => func.airAtomicLoad(inst),
         .atomic_store_unordered,
         .atomic_store_monotonic,
         .atomic_store_release,
         .atomic_store_seq_cst,
         // in WebAssembly, all atomic instructions are sequentially ordered.
         => func.airAtomicStore(inst),
         .atomic_rmw => func.airAtomicRmw(inst),
         .cmpxchg_weak => func.airCmpxchg(inst),
         .cmpxchg_strong => func.airCmpxchg(inst),
         .fence => func.airFence(inst),
 
         .add_optimized,
         .sub_optimized,
         .mul_optimized,
         .div_float_optimized,
         .div_trunc_optimized,
         .div_floor_optimized,
         .div_exact_optimized,
         .rem_optimized,
         .mod_optimized,
         .neg_optimized,
         .cmp_lt_optimized,
         .cmp_lte_optimized,
         .cmp_eq_optimized,
         .cmp_gte_optimized,
         .cmp_gt_optimized,
         .cmp_neq_optimized,
         .cmp_vector_optimized,
         .reduce_optimized,
         .int_from_float_optimized,
         => return func.fail("TODO implement optimized float mode", .{}),
 
         .add_safe,
         .sub_safe,
         .mul_safe,
         => return func.fail("TODO implement safety_checked_instructions", .{}),
 
         .work_item_id,
         .work_group_size,
         .work_group_id,
         => unreachable,
     };
 }
 
 fn genBody(func: *CodeGen, body: []const Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
 
     for (body) |inst| {
         if (func.liveness.isUnused(inst) and !func.air.mustLower(inst, ip)) {
             continue;
         }
         const old_bookkeeping_value = func.air_bookkeeping;
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, Liveness.bpi);
         try func.genInst(inst);
 
         if (builtin.mode == .Debug and func.air_bookkeeping < old_bookkeeping_value + 1) {
             std.debug.panic("Missing call to `finishAir` in AIR instruction %{d} ('{}')", .{
                 inst,
                 func.air.instructions.items(.tag)[@intFromEnum(inst)],
             });
         }
     }
 }
 
 fn airRet(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const fn_info = mod.typeToFunc(func.decl.ty).?;
     const ret_ty = Type.fromInterned(fn_info.return_type);
 
     // result must be stored in the stack and we return a pointer
     // to the stack instead
     if (func.return_value != .none) {
         try func.store(func.return_value, operand, ret_ty, 0);
     } else if (fn_info.cc == .C and ret_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         switch (ret_ty.zigTypeTag(mod)) {
             // Aggregate types can be lowered as a singular value
             .Struct, .Union => {
                 const scalar_type = abi.scalarType(ret_ty, mod);
                 try func.emitWValue(operand);
                 const opcode = buildOpcode(.{
                     .op = .load,
                     .width = @as(u8, @intCast(scalar_type.abiSize(mod) * 8)),
                     .signedness = if (scalar_type.isSignedInt(mod)) .signed else .unsigned,
                     .valtype1 = typeToValtype(scalar_type, mod),
                 });
                 try func.addMemArg(Mir.Inst.Tag.fromOpcode(opcode), .{
                     .offset = operand.offset(),
                     .alignment = @intCast(scalar_type.abiAlignment(mod).toByteUnitsOptional().?),
                 });
             },
             else => try func.emitWValue(operand),
         }
     } else {
         if (!ret_ty.hasRuntimeBitsIgnoreComptime(mod) and ret_ty.isError(mod)) {
             try func.addImm32(0);
         } else {
             try func.emitWValue(operand);
         }
     }
     try func.restoreStackPointer();
     try func.addTag(.@"return");
 
     func.finishAir(inst, .none, &.{un_op});
 }
 
 fn airRetPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const child_type = func.typeOfIndex(inst).childType(mod);
 
     const result = result: {
         if (!child_type.isFnOrHasRuntimeBitsIgnoreComptime(mod)) {
             break :result try func.allocStack(Type.usize); // create pointer to void
         }
 
         const fn_info = mod.typeToFunc(func.decl.ty).?;
         if (firstParamSRet(fn_info.cc, Type.fromInterned(fn_info.return_type), mod)) {
             break :result func.return_value;
         }
 
         break :result try func.allocStackPtr(inst);
     };
 
     func.finishAir(inst, result, &.{});
 }
 
 fn airRetLoad(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const ret_ty = func.typeOf(un_op).childType(mod);
 
     const fn_info = mod.typeToFunc(func.decl.ty).?;
     if (!ret_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         if (ret_ty.isError(mod)) {
             try func.addImm32(0);
         }
     } else if (!firstParamSRet(fn_info.cc, Type.fromInterned(fn_info.return_type), mod)) {
         // leave on the stack
         _ = try func.load(operand, ret_ty, 0);
     }
 
     try func.restoreStackPointer();
     try func.addTag(.@"return");
     return func.finishAir(inst, .none, &.{un_op});
 }
 
 fn airCall(func: *CodeGen, inst: Air.Inst.Index, modifier: std.builtin.CallModifier) InnerError!void {
     if (modifier == .always_tail) return func.fail("TODO implement tail calls for wasm", .{});
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const extra = func.air.extraData(Air.Call, pl_op.payload);
     const args = @as([]const Air.Inst.Ref, @ptrCast(func.air.extra[extra.end..][0..extra.data.args_len]));
     const ty = func.typeOf(pl_op.operand);
 
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const fn_ty = switch (ty.zigTypeTag(mod)) {
         .Fn => ty,
         .Pointer => ty.childType(mod),
         else => unreachable,
     };
     const ret_ty = fn_ty.fnReturnType(mod);
     const fn_info = mod.typeToFunc(fn_ty).?;
     const first_param_sret = firstParamSRet(fn_info.cc, Type.fromInterned(fn_info.return_type), mod);
 
     const callee: ?InternPool.DeclIndex = blk: {
         const func_val = (try func.air.value(pl_op.operand, mod)) orelse break :blk null;
 
         if (func_val.getFunction(mod)) |function| {
             _ = try func.bin_file.getOrCreateAtomForDecl(function.owner_decl);
             break :blk function.owner_decl;
         } else if (func_val.getExternFunc(mod)) |extern_func| {
             const ext_decl = mod.declPtr(extern_func.decl);
             const ext_info = mod.typeToFunc(ext_decl.ty).?;
             var func_type = try genFunctype(func.gpa, ext_info.cc, ext_info.param_types.get(ip), Type.fromInterned(ext_info.return_type), mod);
             defer func_type.deinit(func.gpa);
             const atom_index = try func.bin_file.getOrCreateAtomForDecl(extern_func.decl);
             const atom = func.bin_file.getAtomPtr(atom_index);
             const type_index = try func.bin_file.storeDeclType(extern_func.decl, func_type);
             try func.bin_file.addOrUpdateImport(
                 mod.intern_pool.stringToSlice(ext_decl.name),
                 atom.getSymbolIndex().?,
                 mod.intern_pool.stringToSliceUnwrap(ext_decl.getOwnedExternFunc(mod).?.lib_name),
                 type_index,
             );
             break :blk extern_func.decl;
         } else switch (mod.intern_pool.indexToKey(func_val.ip_index)) {
             .ptr => |ptr| switch (ptr.addr) {
                 .decl => |decl| {
                     _ = try func.bin_file.getOrCreateAtomForDecl(decl);
                     break :blk decl;
                 },
                 else => {},
             },
             else => {},
         }
         return func.fail("Expected a function, but instead found type '{}'", .{func_val.tag()});
     };
 
     const sret = if (first_param_sret) blk: {
         const sret_local = try func.allocStack(ret_ty);
         try func.lowerToStack(sret_local);
         break :blk sret_local;
     } else WValue{ .none = {} };
 
     for (args) |arg| {
         const arg_val = try func.resolveInst(arg);
 
         const arg_ty = func.typeOf(arg);
         if (!arg_ty.hasRuntimeBitsIgnoreComptime(mod)) continue;
 
         try func.lowerArg(mod.typeToFunc(fn_ty).?.cc, arg_ty, arg_val);
     }
 
     if (callee) |direct| {
         const atom_index = func.bin_file.decls.get(direct).?;
         try func.addLabel(.call, func.bin_file.getAtom(atom_index).sym_index);
     } else {
         // in this case we call a function pointer
         // so load its value onto the stack
         std.debug.assert(ty.zigTypeTag(mod) == .Pointer);
         const operand = try func.resolveInst(pl_op.operand);
         try func.emitWValue(operand);
 
         var fn_type = try genFunctype(func.gpa, fn_info.cc, fn_info.param_types.get(ip), Type.fromInterned(fn_info.return_type), mod);
         defer fn_type.deinit(func.gpa);
 
         const fn_type_index = try func.bin_file.putOrGetFuncType(fn_type);
         try func.addLabel(.call_indirect, fn_type_index);
     }
 
     const result_value = result_value: {
         if (!ret_ty.hasRuntimeBitsIgnoreComptime(mod) and !ret_ty.isError(mod)) {
             break :result_value WValue{ .none = {} };
         } else if (ret_ty.isNoReturn(mod)) {
             try func.addTag(.@"unreachable");
             break :result_value WValue{ .none = {} };
         } else if (first_param_sret) {
             break :result_value sret;
             // TODO: Make this less fragile and optimize
         } else if (mod.typeToFunc(fn_ty).?.cc == .C and ret_ty.zigTypeTag(mod) == .Struct or ret_ty.zigTypeTag(mod) == .Union) {
             const result_local = try func.allocLocal(ret_ty);
             try func.addLabel(.local_set, result_local.local.value);
             const scalar_type = abi.scalarType(ret_ty, mod);
             const result = try func.allocStack(scalar_type);
             try func.store(result, result_local, scalar_type, 0);
             break :result_value result;
         } else {
             const result_local = try func.allocLocal(ret_ty);
             try func.addLabel(.local_set, result_local.local.value);
             break :result_value result_local;
         }
     };
 
     var bt = try func.iterateBigTomb(inst, 1 + args.len);
     bt.feed(pl_op.operand);
     for (args) |arg| bt.feed(arg);
     return bt.finishAir(result_value);
 }
 
 fn airAlloc(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const value = try func.allocStackPtr(inst);
     func.finishAir(inst, value, &.{});
 }
 
 fn airStore(func: *CodeGen, inst: Air.Inst.Index, safety: bool) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     if (safety) {
         // TODO if the value is undef, write 0xaa bytes to dest
     } else {
         // TODO if the value is undef, don't lower this instruction
     }
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const ptr_ty = func.typeOf(bin_op.lhs);
     const ptr_info = ptr_ty.ptrInfo(mod);
     const ty = ptr_ty.childType(mod);
 
     if (ptr_info.packed_offset.host_size == 0) {
         try func.store(lhs, rhs, ty, 0);
     } else {
         // at this point we have a non-natural alignment, we must
         // load the value, and then shift+or the rhs into the result location.
         const int_elem_ty = try mod.intType(.unsigned, ptr_info.packed_offset.host_size * 8);
 
         if (isByRef(int_elem_ty, mod)) {
             return func.fail("TODO: airStore for pointers to bitfields with backing type larger than 64bits", .{});
         }
 
         var mask = @as(u64, @intCast((@as(u65, 1) << @as(u7, @intCast(ty.bitSize(mod)))) - 1));
         mask <<= @as(u6, @intCast(ptr_info.packed_offset.bit_offset));
         mask ^= ~@as(u64, 0);
         const shift_val = if (ptr_info.packed_offset.host_size <= 4)
             WValue{ .imm32 = ptr_info.packed_offset.bit_offset }
         else
             WValue{ .imm64 = ptr_info.packed_offset.bit_offset };
         const mask_val = if (ptr_info.packed_offset.host_size <= 4)
             WValue{ .imm32 = @as(u32, @truncate(mask)) }
         else
             WValue{ .imm64 = mask };
 
         try func.emitWValue(lhs);
         const loaded = try func.load(lhs, int_elem_ty, 0);
         const anded = try func.binOp(loaded, mask_val, int_elem_ty, .@"and");
         const extended_value = try func.intcast(rhs, ty, int_elem_ty);
         const shifted_value = if (ptr_info.packed_offset.bit_offset > 0) shifted: {
             break :shifted try func.binOp(extended_value, shift_val, int_elem_ty, .shl);
         } else extended_value;
         const result = try func.binOp(anded, shifted_value, int_elem_ty, .@"or");
         // lhs is still on the stack
         try func.store(.stack, result, int_elem_ty, lhs.offset());
     }
 
     func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn store(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, offset: u32) InnerError!void {
     assert(!(lhs != .stack and rhs == .stack));
     const mod = func.bin_file.base.comp.module.?;
     const abi_size = ty.abiSize(mod);
     switch (ty.zigTypeTag(mod)) {
         .ErrorUnion => {
             const pl_ty = ty.errorUnionPayload(mod);
             if (!pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
                 return func.store(lhs, rhs, Type.anyerror, 0);
             }
 
             const len = @as(u32, @intCast(abi_size));
             return func.memcpy(lhs, rhs, .{ .imm32 = len });
         },
         .Optional => {
             if (ty.isPtrLikeOptional(mod)) {
                 return func.store(lhs, rhs, Type.usize, 0);
             }
             const pl_ty = ty.optionalChild(mod);
             if (!pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
                 return func.store(lhs, rhs, Type.u8, 0);
             }
             if (pl_ty.zigTypeTag(mod) == .ErrorSet) {
                 return func.store(lhs, rhs, Type.anyerror, 0);
             }
 
             const len = @as(u32, @intCast(abi_size));
             return func.memcpy(lhs, rhs, .{ .imm32 = len });
         },
         .Struct, .Array, .Union => if (isByRef(ty, mod)) {
             const len = @as(u32, @intCast(abi_size));
             return func.memcpy(lhs, rhs, .{ .imm32 = len });
         },
         .Vector => switch (determineSimdStoreStrategy(ty, mod)) {
             .unrolled => {
                 const len: u32 = @intCast(abi_size);
                 return func.memcpy(lhs, rhs, .{ .imm32 = len });
             },
             .direct => {
                 try func.emitWValue(lhs);
                 try func.lowerToStack(rhs);
                 // TODO: Add helper functions for simd opcodes
                 const extra_index: u32 = @intCast(func.mir_extra.items.len);
                 // stores as := opcode, offset, alignment (opcode::memarg)
                 try func.mir_extra.appendSlice(func.gpa, &[_]u32{
                     std.wasm.simdOpcode(.v128_store),
                     offset + lhs.offset(),
                     @intCast(ty.abiAlignment(mod).toByteUnits(0)),
                 });
                 return func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
             },
         },
         .Pointer => {
             if (ty.isSlice(mod)) {
                 // store pointer first
                 // lower it to the stack so we do not have to store rhs into a local first
                 try func.emitWValue(lhs);
                 const ptr_local = try func.load(rhs, Type.usize, 0);
                 try func.store(.{ .stack = {} }, ptr_local, Type.usize, 0 + lhs.offset());
 
                 // retrieve length from rhs, and store that alongside lhs as well
                 try func.emitWValue(lhs);
                 const len_local = try func.load(rhs, Type.usize, func.ptrSize());
                 try func.store(.{ .stack = {} }, len_local, Type.usize, func.ptrSize() + lhs.offset());
                 return;
             }
         },
         .Int, .Float => if (abi_size > 8 and abi_size <= 16) {
             try func.emitWValue(lhs);
             const lsb = try func.load(rhs, Type.u64, 0);
             try func.store(.{ .stack = {} }, lsb, Type.u64, 0 + lhs.offset());
 
             try func.emitWValue(lhs);
             const msb = try func.load(rhs, Type.u64, 8);
             try func.store(.{ .stack = {} }, msb, Type.u64, 8 + lhs.offset());
             return;
         } else if (abi_size > 16) {
             try func.memcpy(lhs, rhs, .{ .imm32 = @as(u32, @intCast(ty.abiSize(mod))) });
         },
         else => if (abi_size > 8) {
             return func.fail("TODO: `store` for type `{}` with abisize `{d}`", .{
                 ty.fmt(func.bin_file.base.comp.module.?),
                 abi_size,
             });
         },
     }
     try func.emitWValue(lhs);
     // In this case we're actually interested in storing the stack position
     // into lhs, so we calculate that and emit that instead
     try func.lowerToStack(rhs);
 
     const valtype = typeToValtype(ty, mod);
     const opcode = buildOpcode(.{
         .valtype1 = valtype,
         .width = @as(u8, @intCast(abi_size * 8)),
         .op = .store,
     });
 
     // store rhs value at stack pointer's location in memory
     try func.addMemArg(
         Mir.Inst.Tag.fromOpcode(opcode),
         .{
             .offset = offset + lhs.offset(),
             .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         },
     );
 }
 
 fn airLoad(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     const ty = ty_op.ty.toType();
     const ptr_ty = func.typeOf(ty_op.operand);
     const ptr_info = ptr_ty.ptrInfo(mod);
 
     if (!ty.hasRuntimeBitsIgnoreComptime(mod)) return func.finishAir(inst, .none, &.{ty_op.operand});
 
     const result = result: {
         if (isByRef(ty, mod)) {
             const new_local = try func.allocStack(ty);
             try func.store(new_local, operand, ty, 0);
             break :result new_local;
         }
 
         if (ptr_info.packed_offset.host_size == 0) {
             const stack_loaded = try func.load(operand, ty, 0);
             break :result try stack_loaded.toLocal(func, ty);
         }
 
         // at this point we have a non-natural alignment, we must
         // shift the value to obtain the correct bit.
         const int_elem_ty = try mod.intType(.unsigned, ptr_info.packed_offset.host_size * 8);
         const shift_val = if (ptr_info.packed_offset.host_size <= 4)
             WValue{ .imm32 = ptr_info.packed_offset.bit_offset }
         else if (ptr_info.packed_offset.host_size <= 8)
             WValue{ .imm64 = ptr_info.packed_offset.bit_offset }
         else
             return func.fail("TODO: airLoad where ptr to bitfield exceeds 64 bits", .{});
 
         const stack_loaded = try func.load(operand, int_elem_ty, 0);
         const shifted = try func.binOp(stack_loaded, shift_val, int_elem_ty, .shr);
         const result = try func.trunc(shifted, ty, int_elem_ty);
         // const wrapped = try func.wrapOperand(shifted, ty);
         break :result try result.toLocal(func, ty);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 /// Loads an operand from the linear memory section.
 /// NOTE: Leaves the value on the stack.
 fn load(func: *CodeGen, operand: WValue, ty: Type, offset: u32) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     // load local's value from memory by its stack position
     try func.emitWValue(operand);
 
     if (ty.zigTypeTag(mod) == .Vector) {
         // TODO: Add helper functions for simd opcodes
         const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
         // stores as := opcode, offset, alignment (opcode::memarg)
         try func.mir_extra.appendSlice(func.gpa, &[_]u32{
             std.wasm.simdOpcode(.v128_load),
             offset + operand.offset(),
             @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         });
         try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
         return WValue{ .stack = {} };
     }
 
     const abi_size = @as(u8, @intCast(ty.abiSize(mod)));
     const opcode = buildOpcode(.{
         .valtype1 = typeToValtype(ty, mod),
         .width = abi_size * 8,
         .op = .load,
         .signedness = .unsigned,
     });
 
     try func.addMemArg(
         Mir.Inst.Tag.fromOpcode(opcode),
         .{
             .offset = offset + operand.offset(),
             .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         },
     );
 
     return WValue{ .stack = {} };
 }
 
 fn airArg(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const arg_index = func.arg_index;
     const arg = func.args[arg_index];
     const cc = mod.typeToFunc(func.decl.ty).?.cc;
     const arg_ty = func.typeOfIndex(inst);
     if (cc == .C) {
         const arg_classes = abi.classifyType(arg_ty, mod);
         for (arg_classes) |class| {
             if (class != .none) {
                 func.arg_index += 1;
             }
         }
 
         // When we have an argument that's passed using more than a single parameter,
         // we combine them into a single stack value
         if (arg_classes[0] == .direct and arg_classes[1] == .direct) {
             if (arg_ty.zigTypeTag(mod) != .Int and arg_ty.zigTypeTag(mod) != .Float) {
                 return func.fail(
                     "TODO: Implement C-ABI argument for type '{}'",
                     .{arg_ty.fmt(func.bin_file.base.comp.module.?)},
                 );
             }
             const result = try func.allocStack(arg_ty);
             try func.store(result, arg, Type.u64, 0);
             try func.store(result, func.args[arg_index + 1], Type.u64, 8);
             return func.finishAir(inst, result, &.{});
         }
     } else {
         func.arg_index += 1;
     }
 
     switch (func.debug_output) {
         .dwarf => |dwarf| {
             const src_index = func.air.instructions.items(.data)[@intFromEnum(inst)].arg.src_index;
             const name = mod.getParamName(func.func_index, src_index);
             try dwarf.genArgDbgInfo(name, arg_ty, mod.funcOwnerDeclIndex(func.func_index), .{
                 .wasm_local = arg.local.value,
             });
         },
         else => {},
     }
 
     func.finishAir(inst, arg, &.{});
 }
 
 fn airBinOp(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const lhs_ty = func.typeOf(bin_op.lhs);
     const rhs_ty = func.typeOf(bin_op.rhs);
 
     // For certain operations, such as shifting, the types are different.
     // When converting this to a WebAssembly type, they *must* match to perform
     // an operation. For this reason we verify if the WebAssembly type is different, in which
     // case we first coerce the operands to the same type before performing the operation.
     // For big integers we can ignore this as we will call into compiler-rt which handles this.
     const result = switch (op) {
         .shr, .shl => res: {
             const lhs_wasm_bits = toWasmBits(@as(u16, @intCast(lhs_ty.bitSize(mod)))) orelse {
                 return func.fail("TODO: implement '{s}' for types larger than 128 bits", .{@tagName(op)});
             };
             const rhs_wasm_bits = toWasmBits(@as(u16, @intCast(rhs_ty.bitSize(mod)))).?;
             const new_rhs = if (lhs_wasm_bits != rhs_wasm_bits and lhs_wasm_bits != 128) blk: {
                 const tmp = try func.intcast(rhs, rhs_ty, lhs_ty);
                 break :blk try tmp.toLocal(func, lhs_ty);
             } else rhs;
             const stack_result = try func.binOp(lhs, new_rhs, lhs_ty, op);
             break :res try stack_result.toLocal(func, lhs_ty);
         },
         else => res: {
             const stack_result = try func.binOp(lhs, rhs, lhs_ty, op);
             break :res try stack_result.toLocal(func, lhs_ty);
         },
     };
 
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Performs a binary operation on the given `WValue`'s
 /// NOTE: THis leaves the value on top of the stack.
 fn binOp(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, op: Op) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(!(lhs != .stack and rhs == .stack));
 
     if (ty.isAnyFloat()) {
         const float_op = FloatOp.fromOp(op);
         return func.floatOp(float_op, ty, &.{ lhs, rhs });
     }
 
     if (isByRef(ty, mod)) {
         if (ty.zigTypeTag(mod) == .Int) {
             return func.binOpBigInt(lhs, rhs, ty, op);
         } else {
             return func.fail(
                 "TODO: Implement binary operation for type: {}",
                 .{ty.fmt(func.bin_file.base.comp.module.?)},
             );
         }
     }
 
     const opcode: wasm.Opcode = buildOpcode(.{
         .op = op,
         .valtype1 = typeToValtype(ty, mod),
         .signedness = if (ty.isSignedInt(mod)) .signed else .unsigned,
     });
     try func.emitWValue(lhs);
     try func.emitWValue(rhs);
 
     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
 
     return WValue{ .stack = {} };
 }
 
 fn binOpBigInt(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, op: Op) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const int_info = ty.intInfo(mod);
     if (int_info.bits > 128) {
         return func.fail("TODO: Implement binary operation for big integers larger than 128 bits", .{});
     }
 
     switch (op) {
         .mul => return func.callIntrinsic("__multi3", &.{ ty.toIntern(), ty.toIntern() }, ty, &.{ lhs, rhs }),
         .div => switch (int_info.signedness) {
             .signed => return func.callIntrinsic("__udivti3", &.{ ty.toIntern(), ty.toIntern() }, ty, &.{ lhs, rhs }),
             .unsigned => return func.callIntrinsic("__divti3", &.{ ty.toIntern(), ty.toIntern() }, ty, &.{ lhs, rhs }),
         },
         .rem => return func.callIntrinsic("__umodti3", &.{ ty.toIntern(), ty.toIntern() }, ty, &.{ lhs, rhs }),
         .shr => return func.callIntrinsic("__lshrti3", &.{ ty.toIntern(), .i32_type }, ty, &.{ lhs, rhs }),
         .shl => return func.callIntrinsic("__ashlti3", &.{ ty.toIntern(), .i32_type }, ty, &.{ lhs, rhs }),
         .xor => {
             const result = try func.allocStack(ty);
             try func.emitWValue(result);
             const lhs_high_bit = try func.load(lhs, Type.u64, 0);
             const rhs_high_bit = try func.load(rhs, Type.u64, 0);
             const xor_high_bit = try func.binOp(lhs_high_bit, rhs_high_bit, Type.u64, .xor);
             try func.store(.stack, xor_high_bit, Type.u64, result.offset());
 
             try func.emitWValue(result);
             const lhs_low_bit = try func.load(lhs, Type.u64, 8);
             const rhs_low_bit = try func.load(rhs, Type.u64, 8);
             const xor_low_bit = try func.binOp(lhs_low_bit, rhs_low_bit, Type.u64, .xor);
             try func.store(.stack, xor_low_bit, Type.u64, result.offset() + 8);
             return result;
         },
         .add, .sub => {
             const result = try func.allocStack(ty);
             var lhs_high_bit = try (try func.load(lhs, Type.u64, 0)).toLocal(func, Type.u64);
             defer lhs_high_bit.free(func);
             var rhs_high_bit = try (try func.load(rhs, Type.u64, 0)).toLocal(func, Type.u64);
             defer rhs_high_bit.free(func);
             var high_op_res = try (try func.binOp(lhs_high_bit, rhs_high_bit, Type.u64, op)).toLocal(func, Type.u64);
             defer high_op_res.free(func);
 
             const lhs_low_bit = try func.load(lhs, Type.u64, 8);
             const rhs_low_bit = try func.load(rhs, Type.u64, 8);
             const low_op_res = try func.binOp(lhs_low_bit, rhs_low_bit, Type.u64, op);
 
             const lt = if (op == .add) blk: {
                 break :blk try func.cmp(high_op_res, rhs_high_bit, Type.u64, .lt);
             } else if (op == .sub) blk: {
                 break :blk try func.cmp(lhs_high_bit, rhs_high_bit, Type.u64, .lt);
             } else unreachable;
             const tmp = try func.intcast(lt, Type.u32, Type.u64);
             var tmp_op = try (try func.binOp(low_op_res, tmp, Type.u64, op)).toLocal(func, Type.u64);
             defer tmp_op.free(func);
 
             try func.store(result, high_op_res, Type.u64, 0);
             try func.store(result, tmp_op, Type.u64, 8);
             return result;
         },
         else => return func.fail("TODO: Implement binary operation for big integers: '{s}'", .{@tagName(op)}),
     }
 }
 
 const FloatOp = enum {
     add,
     ceil,
     cos,
     div,
     exp,
     exp2,
     fabs,
     floor,
     fma,
     fmax,
     fmin,
     fmod,
     log,
     log10,
     log2,
     mul,
     neg,
     round,
     sin,
     sqrt,
     sub,
     tan,
     trunc,
 
     pub fn fromOp(op: Op) FloatOp {
         return switch (op) {
             .add => .add,
             .ceil => .ceil,
             .div => .div,
             .abs => .fabs,
             .floor => .floor,
             .max => .fmax,
             .min => .fmin,
             .mul => .mul,
             .neg => .neg,
             .nearest => .round,
             .sqrt => .sqrt,
             .sub => .sub,
             .trunc => .trunc,
             else => unreachable,
         };
     }
 
     pub fn toOp(float_op: FloatOp) ?Op {
         return switch (float_op) {
             .add => .add,
             .ceil => .ceil,
             .div => .div,
             .fabs => .abs,
             .floor => .floor,
             .fmax => .max,
             .fmin => .min,
             .mul => .mul,
             .neg => .neg,
             .round => .nearest,
             .sqrt => .sqrt,
             .sub => .sub,
             .trunc => .trunc,
 
             .cos,
             .exp,
             .exp2,
             .fma,
             .fmod,
             .log,
             .log10,
             .log2,
             .sin,
             .tan,
             => null,
         };
     }
 };
 
 fn airAbs(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     const ty = func.typeOf(ty_op.operand);
     const scalar_ty = ty.scalarType(mod);
 
     switch (scalar_ty.zigTypeTag(mod)) {
         .Int => if (ty.zigTypeTag(mod) == .Vector) {
             return func.fail("TODO implement airAbs for {}", .{ty.fmt(mod)});
         } else {
             const int_bits = ty.intInfo(mod).bits;
             const wasm_bits = toWasmBits(int_bits) orelse {
                 return func.fail("TODO: airAbs for signed integers larger than '{d}' bits", .{int_bits});
             };
 
             const op = try operand.toLocal(func, ty);
 
             try func.emitWValue(op);
             switch (wasm_bits) {
                 32 => {
                     if (wasm_bits != int_bits) {
                         try func.addImm32(wasm_bits - int_bits);
                         try func.addTag(.i32_shl);
                     }
                     try func.addImm32(31);
                     try func.addTag(.i32_shr_s);
 
                     const tmp = try func.allocLocal(ty);
                     try func.addLabel(.local_tee, tmp.local.value);
 
                     try func.emitWValue(op);
                     try func.addTag(.i32_xor);
                     try func.emitWValue(tmp);
                     try func.addTag(.i32_sub);
 
                     if (int_bits != wasm_bits) {
                         try func.emitWValue(WValue{ .imm32 = (@as(u32, 1) << @intCast(int_bits)) - 1 });
                         try func.addTag(.i32_and);
                     }
                 },
                 64 => {
                     if (wasm_bits != int_bits) {
                         try func.addImm64(wasm_bits - int_bits);
                         try func.addTag(.i64_shl);
                     }
                     try func.addImm64(63);
                     try func.addTag(.i64_shr_s);
 
                     const tmp = try func.allocLocal(ty);
                     try func.addLabel(.local_tee, tmp.local.value);
 
                     try func.emitWValue(op);
                     try func.addTag(.i64_xor);
                     try func.emitWValue(tmp);
                     try func.addTag(.i64_sub);
 
                     if (int_bits != wasm_bits) {
                         try func.emitWValue(WValue{ .imm64 = (@as(u64, 1) << @intCast(int_bits)) - 1 });
                         try func.addTag(.i64_and);
                     }
                 },
                 else => return func.fail("TODO: Implement airAbs for {}", .{ty.fmt(mod)}),
             }
 
             const result = try (WValue{ .stack = {} }).toLocal(func, ty);
             func.finishAir(inst, result, &.{ty_op.operand});
         },
         .Float => {
             const result = try (try func.floatOp(.fabs, ty, &.{operand})).toLocal(func, ty);
             func.finishAir(inst, result, &.{ty_op.operand});
         },
         else => unreachable,
     }
 }
 
 fn airUnaryFloatOp(func: *CodeGen, inst: Air.Inst.Index, op: FloatOp) InnerError!void {
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const ty = func.typeOf(un_op);
 
     const result = try (try func.floatOp(op, ty, &.{operand})).toLocal(func, ty);
     func.finishAir(inst, result, &.{un_op});
 }
 
 fn floatOp(func: *CodeGen, float_op: FloatOp, ty: Type, args: []const WValue) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement floatOps for vectors", .{});
     }
 
     const float_bits = ty.floatBits(func.target);
 
     if (float_op == .neg) {
         return func.floatNeg(ty, args[0]);
     }
 
     if (float_bits == 32 or float_bits == 64) {
         if (float_op.toOp()) |op| {
             for (args) |operand| {
                 try func.emitWValue(operand);
             }
             const opcode = buildOpcode(.{ .op = op, .valtype1 = typeToValtype(ty, mod) });
             try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
             return .stack;
         }
     }
 
     var fn_name_buf: [64]u8 = undefined;
     const fn_name = switch (float_op) {
         .add,
         .sub,
         .div,
         .mul,
         => std.fmt.bufPrint(&fn_name_buf, "__{s}{s}f3", .{
             @tagName(float_op), target_util.compilerRtFloatAbbrev(float_bits),
         }) catch unreachable,
 
         .ceil,
         .cos,
         .exp,
         .exp2,
         .fabs,
         .floor,
         .fma,
         .fmax,
         .fmin,
         .fmod,
         .log,
         .log10,
         .log2,
         .round,
         .sin,
         .sqrt,
         .tan,
         .trunc,
         => std.fmt.bufPrint(&fn_name_buf, "{s}{s}{s}", .{
             target_util.libcFloatPrefix(float_bits), @tagName(float_op), target_util.libcFloatSuffix(float_bits),
         }) catch unreachable,
         .neg => unreachable, // handled above
     };
 
     // fma requires three operands
     var param_types_buffer: [3]InternPool.Index = .{ ty.ip_index, ty.ip_index, ty.ip_index };
     const param_types = param_types_buffer[0..args.len];
     return func.callIntrinsic(fn_name, param_types, ty, args);
 }
 
 /// NOTE: The result value remains on top of the stack.
 fn floatNeg(func: *CodeGen, ty: Type, arg: WValue) InnerError!WValue {
     const float_bits = ty.floatBits(func.target);
     switch (float_bits) {
         16 => {
             try func.emitWValue(arg);
             try func.addImm32(std.math.minInt(i16));
             try func.addTag(.i32_xor);
             return .stack;
         },
         32, 64 => {
             try func.emitWValue(arg);
             const val_type: wasm.Valtype = if (float_bits == 32) .f32 else .f64;
             const opcode = buildOpcode(.{ .op = .neg, .valtype1 = val_type });
             try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
             return .stack;
         },
         80, 128 => {
             const result = try func.allocStack(ty);
             try func.emitWValue(result);
             try func.emitWValue(arg);
             try func.addMemArg(.i64_load, .{ .offset = 0 + arg.offset(), .alignment = 2 });
             try func.addMemArg(.i64_store, .{ .offset = 0 + result.offset(), .alignment = 2 });
 
             try func.emitWValue(result);
             try func.emitWValue(arg);
             try func.addMemArg(.i64_load, .{ .offset = 8 + arg.offset(), .alignment = 2 });
 
             if (float_bits == 80) {
                 try func.addImm64(0x8000);
                 try func.addTag(.i64_xor);
                 try func.addMemArg(.i64_store16, .{ .offset = 8 + result.offset(), .alignment = 2 });
             } else {
                 try func.addImm64(0x8000000000000000);
                 try func.addTag(.i64_xor);
                 try func.addMemArg(.i64_store, .{ .offset = 8 + result.offset(), .alignment = 2 });
             }
             return result;
         },
         else => unreachable,
     }
 }
 
 fn airWrapBinOp(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const lhs_ty = func.typeOf(bin_op.lhs);
     const rhs_ty = func.typeOf(bin_op.rhs);
 
     if (lhs_ty.zigTypeTag(mod) == .Vector or rhs_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement wrapping arithmetic for vectors", .{});
     }
 
     // For certain operations, such as shifting, the types are different.
     // When converting this to a WebAssembly type, they *must* match to perform
     // an operation. For this reason we verify if the WebAssembly type is different, in which
     // case we first coerce the operands to the same type before performing the operation.
     // For big integers we can ignore this as we will call into compiler-rt which handles this.
     const result = switch (op) {
         .shr, .shl => res: {
             const lhs_wasm_bits = toWasmBits(@as(u16, @intCast(lhs_ty.bitSize(mod)))) orelse {
                 return func.fail("TODO: implement '{s}' for types larger than 128 bits", .{@tagName(op)});
             };
             const rhs_wasm_bits = toWasmBits(@as(u16, @intCast(rhs_ty.bitSize(mod)))).?;
             const new_rhs = if (lhs_wasm_bits != rhs_wasm_bits and lhs_wasm_bits != 128) blk: {
                 const tmp = try func.intcast(rhs, rhs_ty, lhs_ty);
                 break :blk try tmp.toLocal(func, lhs_ty);
             } else rhs;
             const stack_result = try func.wrapBinOp(lhs, new_rhs, lhs_ty, op);
             break :res try stack_result.toLocal(func, lhs_ty);
         },
         else => res: {
             const stack_result = try func.wrapBinOp(lhs, rhs, lhs_ty, op);
             break :res try stack_result.toLocal(func, lhs_ty);
         },
     };
 
     return func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Performs a wrapping binary operation.
 /// Asserts rhs is not a stack value when lhs also isn't.
 /// NOTE: Leaves the result on the stack when its Type is <= 64 bits
 fn wrapBinOp(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, op: Op) InnerError!WValue {
     const bin_local = try func.binOp(lhs, rhs, ty, op);
     return func.wrapOperand(bin_local, ty);
 }
 
 /// Wraps an operand based on a given type's bitsize.
 /// Asserts `Type` is <= 128 bits.
 /// NOTE: When the Type is <= 64 bits, leaves the value on top of the stack.
 fn wrapOperand(func: *CodeGen, operand: WValue, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(ty.abiSize(mod) <= 16);
     const bitsize = @as(u16, @intCast(ty.bitSize(mod)));
     const wasm_bits = toWasmBits(bitsize) orelse {
         return func.fail("TODO: Implement wrapOperand for bitsize '{d}'", .{bitsize});
     };
 
     if (wasm_bits == bitsize) return operand;
 
     if (wasm_bits == 128) {
         assert(operand != .stack);
         const lsb = try func.load(operand, Type.u64, 8);
 
         const result_ptr = try func.allocStack(ty);
         try func.emitWValue(result_ptr);
         try func.store(.{ .stack = {} }, lsb, Type.u64, 8 + result_ptr.offset());
         const result = (@as(u64, 1) << @as(u6, @intCast(64 - (wasm_bits - bitsize)))) - 1;
         try func.emitWValue(result_ptr);
         _ = try func.load(operand, Type.u64, 0);
         try func.addImm64(result);
         try func.addTag(.i64_and);
         try func.addMemArg(.i64_store, .{ .offset = result_ptr.offset(), .alignment = 8 });
         return result_ptr;
     }
 
     const result = (@as(u64, 1) << @as(u6, @intCast(bitsize))) - 1;
     try func.emitWValue(operand);
     if (bitsize <= 32) {
         try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(result)))));
         try func.addTag(.i32_and);
     } else if (bitsize <= 64) {
         try func.addImm64(result);
         try func.addTag(.i64_and);
     } else unreachable;
 
     return WValue{ .stack = {} };
 }
 
 fn lowerParentPtr(func: *CodeGen, ptr_val: Value, offset: u32) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const ptr = mod.intern_pool.indexToKey(ptr_val.ip_index).ptr;
     switch (ptr.addr) {
         .decl => |decl_index| {
             return func.lowerParentPtrDecl(ptr_val, decl_index, offset);
         },
         .anon_decl => |ad| return func.lowerAnonDeclRef(ad, offset),
         .mut_decl => |mut_decl| {
             const decl_index = mut_decl.decl;
             return func.lowerParentPtrDecl(ptr_val, decl_index, offset);
         },
         .eu_payload => |tag| return func.fail("TODO: Implement lowerParentPtr for {}", .{tag}),
         .int => |base| return func.lowerConstant(Value.fromInterned(base), Type.usize),
         .opt_payload => |base_ptr| return func.lowerParentPtr(Value.fromInterned(base_ptr), offset),
         .comptime_field => unreachable,
         .elem => |elem| {
             const index = elem.index;
             const elem_type = Type.fromInterned(mod.intern_pool.typeOf(elem.base)).elemType2(mod);
             const elem_offset = index * elem_type.abiSize(mod);
             return func.lowerParentPtr(Value.fromInterned(elem.base), @as(u32, @intCast(elem_offset + offset)));
         },
         .field => |field| {
             const parent_ptr_ty = Type.fromInterned(mod.intern_pool.typeOf(field.base));
             const parent_ty = parent_ptr_ty.childType(mod);
             const field_index: u32 = @intCast(field.index);
 
             const field_offset = switch (parent_ty.zigTypeTag(mod)) {
                 .Struct => blk: {
                     if (mod.typeToPackedStruct(parent_ty)) |struct_type| {
                         if (Type.fromInterned(ptr.ty).ptrInfo(mod).packed_offset.host_size == 0)
                             break :blk @divExact(mod.structPackedFieldBitOffset(struct_type, field_index) + parent_ptr_ty.ptrInfo(mod).packed_offset.bit_offset, 8)
                         else
                             break :blk 0;
                     }
                     break :blk parent_ty.structFieldOffset(field_index, mod);
                 },
                 .Union => switch (parent_ty.containerLayout(mod)) {
                     .Packed => 0,
                     else => blk: {
                         const layout: Module.UnionLayout = parent_ty.unionGetLayout(mod);
                         if (layout.payload_size == 0) break :blk 0;
                         if (layout.payload_align.compare(.gt, layout.tag_align)) break :blk 0;
 
                         // tag is stored first so calculate offset from where payload starts
                         break :blk layout.tag_align.forward(layout.tag_size);
                     },
                 },
                 .Pointer => switch (parent_ty.ptrSize(mod)) {
                     .Slice => switch (field.index) {
                         0 => 0,
                         1 => func.ptrSize(),
                         else => unreachable,
                     },
                     else => unreachable,
                 },
                 else => unreachable,
             };
             return func.lowerParentPtr(Value.fromInterned(field.base), @as(u32, @intCast(offset + field_offset)));
         },
     }
 }
 
 fn lowerParentPtrDecl(func: *CodeGen, ptr_val: Value, decl_index: InternPool.DeclIndex, offset: u32) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const decl = mod.declPtr(decl_index);
     try mod.markDeclAlive(decl);
     const ptr_ty = try mod.singleMutPtrType(decl.ty);
     return func.lowerDeclRefValue(.{ .ty = ptr_ty, .val = ptr_val }, decl_index, offset);
 }
 
 fn lowerAnonDeclRef(
     func: *CodeGen,
     anon_decl: InternPool.Key.Ptr.Addr.AnonDecl,
     offset: u32,
 ) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const decl_val = anon_decl.val;
     const ty = Type.fromInterned(mod.intern_pool.typeOf(decl_val));
 
     const is_fn_body = ty.zigTypeTag(mod) == .Fn;
     if (!is_fn_body and !ty.hasRuntimeBitsIgnoreComptime(mod)) {
         return WValue{ .imm32 = 0xaaaaaaaa };
     }
 
     const decl_align = mod.intern_pool.indexToKey(anon_decl.orig_ty).ptr_type.flags.alignment;
     const res = try func.bin_file.lowerAnonDecl(decl_val, decl_align, func.decl.srcLoc(mod));
     switch (res) {
         .ok => {},
         .fail => |em| {
             func.err_msg = em;
             return error.CodegenFail;
         },
     }
     const target_atom_index = func.bin_file.anon_decls.get(decl_val).?;
     const target_sym_index = func.bin_file.getAtom(target_atom_index).getSymbolIndex().?;
     if (is_fn_body) {
         return WValue{ .function_index = target_sym_index };
     } else if (offset == 0) {
         return WValue{ .memory = target_sym_index };
     } else return WValue{ .memory_offset = .{ .pointer = target_sym_index, .offset = offset } };
 }
 
 fn lowerDeclRefValue(func: *CodeGen, tv: TypedValue, decl_index: InternPool.DeclIndex, offset: u32) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     if (tv.ty.isSlice(mod)) {
         return WValue{ .memory = try func.bin_file.lowerUnnamedConst(tv, decl_index) };
     }
 
     const decl = mod.declPtr(decl_index);
     // check if decl is an alias to a function, in which case we
     // want to lower the actual decl, rather than the alias itself.
     if (decl.val.getFunction(mod)) |func_val| {
         if (func_val.owner_decl != decl_index) {
             return func.lowerDeclRefValue(tv, func_val.owner_decl, offset);
         }
     } else if (decl.val.getExternFunc(mod)) |func_val| {
         if (func_val.decl != decl_index) {
             return func.lowerDeclRefValue(tv, func_val.decl, offset);
         }
     }
     if (decl.ty.zigTypeTag(mod) != .Fn and !decl.ty.hasRuntimeBitsIgnoreComptime(mod)) {
         return WValue{ .imm32 = 0xaaaaaaaa };
     }
 
     try mod.markDeclAlive(decl);
     const atom_index = try func.bin_file.getOrCreateAtomForDecl(decl_index);
     const atom = func.bin_file.getAtom(atom_index);
 
     const target_sym_index = atom.sym_index;
     if (decl.ty.zigTypeTag(mod) == .Fn) {
         try func.bin_file.addTableFunction(target_sym_index);
         return WValue{ .function_index = target_sym_index };
     } else if (offset == 0) {
         return WValue{ .memory = target_sym_index };
     } else return WValue{ .memory_offset = .{ .pointer = target_sym_index, .offset = offset } };
 }
 
 /// Converts a signed integer to its 2's complement form and returns
 /// an unsigned integer instead.
 /// Asserts bitsize <= 64
 fn toTwosComplement(value: anytype, bits: u7) std.meta.Int(.unsigned, @typeInfo(@TypeOf(value)).Int.bits) {
     const T = @TypeOf(value);
     comptime assert(@typeInfo(T) == .Int);
     comptime assert(@typeInfo(T).Int.signedness == .signed);
     assert(bits <= 64);
     const WantedT = std.meta.Int(.unsigned, @typeInfo(T).Int.bits);
     if (value >= 0) return @as(WantedT, @bitCast(value));
     const max_value = @as(u64, @intCast((@as(u65, 1) << bits) - 1));
     const flipped = @as(T, @intCast((~-@as(i65, value)) + 1));
     const result = @as(WantedT, @bitCast(flipped)) & max_value;
     return @as(WantedT, @intCast(result));
 }
 
 /// This function is intended to assert that `isByRef` returns `false` for `ty`.
 /// However such an assertion fails on the behavior tests currently.
 fn lowerConstant(func: *CodeGen, val: Value, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     // TODO: enable this assertion
     //assert(!isByRef(ty, mod));
     const ip = &mod.intern_pool;
     if (val.isUndefDeep(mod)) return func.emitUndefined(ty);
 
     switch (ip.indexToKey(val.ip_index)) {
         .int_type,
         .ptr_type,
         .array_type,
         .vector_type,
         .opt_type,
         .anyframe_type,
         .error_union_type,
         .simple_type,
         .struct_type,
         .anon_struct_type,
         .union_type,
         .opaque_type,
         .enum_type,
         .func_type,
         .error_set_type,
         .inferred_error_set_type,
         => unreachable, // types, not values
 
         .undef => unreachable, // handled above
         .simple_value => |simple_value| switch (simple_value) {
             .undefined,
             .void,
             .null,
             .empty_struct,
             .@"unreachable",
             .generic_poison,
             => unreachable, // non-runtime values
             .false, .true => return WValue{ .imm32 = switch (simple_value) {
                 .false => 0,
                 .true => 1,
                 else => unreachable,
             } },
         },
         .variable,
         .extern_func,
         .func,
         .enum_literal,
         .empty_enum_value,
         => unreachable, // non-runtime values
         .int => {
             const int_info = ty.intInfo(mod);
             switch (int_info.signedness) {
                 .signed => switch (int_info.bits) {
                     0...32 => return WValue{ .imm32 = @as(u32, @intCast(toTwosComplement(
                         val.toSignedInt(mod),
                         @as(u6, @intCast(int_info.bits)),
                     ))) },
                     33...64 => return WValue{ .imm64 = toTwosComplement(
                         val.toSignedInt(mod),
                         @as(u7, @intCast(int_info.bits)),
                     ) },
                     else => unreachable,
                 },
                 .unsigned => switch (int_info.bits) {
                     0...32 => return WValue{ .imm32 = @as(u32, @intCast(val.toUnsignedInt(mod))) },
                     33...64 => return WValue{ .imm64 = val.toUnsignedInt(mod) },
                     else => unreachable,
                 },
             }
         },
         .err => |err| {
             const int = try mod.getErrorValue(err.name);
             return WValue{ .imm32 = int };
         },
         .error_union => |error_union| {
             const err_int_ty = try mod.errorIntType();
             const err_tv: TypedValue = switch (error_union.val) {
                 .err_name => |err_name| .{
                     .ty = ty.errorUnionSet(mod),
                     .val = Value.fromInterned((try mod.intern(.{ .err = .{
                         .ty = ty.errorUnionSet(mod).toIntern(),
                         .name = err_name,
                     } }))),
                 },
                 .payload => .{
                     .ty = err_int_ty,
                     .val = try mod.intValue(err_int_ty, 0),
                 },
             };
             const payload_type = ty.errorUnionPayload(mod);
             if (!payload_type.hasRuntimeBitsIgnoreComptime(mod)) {
                 // We use the error type directly as the type.
                 return func.lowerConstant(err_tv.val, err_tv.ty);
             }
 
             return func.fail("Wasm TODO: lowerConstant error union with non-zero-bit payload type", .{});
         },
         .enum_tag => |enum_tag| {
             const int_tag_ty = ip.typeOf(enum_tag.int);
             return func.lowerConstant(Value.fromInterned(enum_tag.int), Type.fromInterned(int_tag_ty));
         },
         .float => |float| switch (float.storage) {
             .f16 => |f16_val| return WValue{ .imm32 = @as(u16, @bitCast(f16_val)) },
             .f32 => |f32_val| return WValue{ .float32 = f32_val },
             .f64 => |f64_val| return WValue{ .float64 = f64_val },
             else => unreachable,
         },
         .ptr => |ptr| switch (ptr.addr) {
             .decl => |decl| return func.lowerDeclRefValue(.{ .ty = ty, .val = val }, decl, 0),
             .mut_decl => |mut_decl| return func.lowerDeclRefValue(.{ .ty = ty, .val = val }, mut_decl.decl, 0),
             .int => |int| return func.lowerConstant(Value.fromInterned(int), Type.fromInterned(ip.typeOf(int))),
             .opt_payload, .elem, .field => return func.lowerParentPtr(val, 0),
             .anon_decl => |ad| return func.lowerAnonDeclRef(ad, 0),
             else => return func.fail("Wasm TODO: lowerConstant for other const addr tag {}", .{ptr.addr}),
         },
         .opt => if (ty.optionalReprIsPayload(mod)) {
             const pl_ty = ty.optionalChild(mod);
             if (val.optionalValue(mod)) |payload| {
                 return func.lowerConstant(payload, pl_ty);
             } else {
                 return WValue{ .imm32 = 0 };
             }
         } else {
             return WValue{ .imm32 = @intFromBool(!val.isNull(mod)) };
         },
         .aggregate => switch (ip.indexToKey(ty.ip_index)) {
             .array_type => return func.fail("Wasm TODO: LowerConstant for {}", .{ty.fmt(mod)}),
             .vector_type => {
                 assert(determineSimdStoreStrategy(ty, mod) == .direct);
                 var buf: [16]u8 = undefined;
                 val.writeToMemory(ty, mod, &buf) catch unreachable;
                 return func.storeSimdImmd(buf);
             },
             .struct_type => |struct_type| {
                 // non-packed structs are not handled in this function because they
                 // are by-ref types.
                 assert(struct_type.layout == .Packed);
                 var buf: [8]u8 = .{0} ** 8; // zero the buffer so we do not read 0xaa as integer
                 val.writeToPackedMemory(ty, mod, &buf, 0) catch unreachable;
                 const backing_int_ty = Type.fromInterned(struct_type.backingIntType(ip).*);
                 const int_val = try mod.intValue(
                     backing_int_ty,
                     mem.readInt(u64, &buf, .little),
                 );
                 return func.lowerConstant(int_val, backing_int_ty);
             },
             else => unreachable,
         },
         .un => |un| {
             // in this case we have a packed union which will not be passed by reference.
             const constant_ty = if (un.tag == .none)
                 try ty.unionBackingType(mod)
             else field_ty: {
                 const union_obj = mod.typeToUnion(ty).?;
                 const field_index = mod.unionTagFieldIndex(union_obj, Value.fromInterned(un.tag)).?;
                 break :field_ty Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
             };
             return func.lowerConstant(Value.fromInterned(un.val), constant_ty);
         },
         .memoized_call => unreachable,
     }
 }
 
 /// Stores the value as a 128bit-immediate value by storing it inside
 /// the list and returning the index into this list as `WValue`.
 fn storeSimdImmd(func: *CodeGen, value: [16]u8) !WValue {
     const index = @as(u32, @intCast(func.simd_immediates.items.len));
     try func.simd_immediates.append(func.gpa, value);
     return WValue{ .imm128 = index };
 }
 
 fn emitUndefined(func: *CodeGen, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     switch (ty.zigTypeTag(mod)) {
         .Bool, .ErrorSet => return WValue{ .imm32 = 0xaaaaaaaa },
         .Int, .Enum => switch (ty.intInfo(mod).bits) {
             0...32 => return WValue{ .imm32 = 0xaaaaaaaa },
             33...64 => return WValue{ .imm64 = 0xaaaaaaaaaaaaaaaa },
             else => unreachable,
         },
         .Float => switch (ty.floatBits(func.target)) {
             16 => return WValue{ .imm32 = 0xaaaaaaaa },
             32 => return WValue{ .float32 = @as(f32, @bitCast(@as(u32, 0xaaaaaaaa))) },
             64 => return WValue{ .float64 = @as(f64, @bitCast(@as(u64, 0xaaaaaaaaaaaaaaaa))) },
             else => unreachable,
         },
         .Pointer => switch (func.arch()) {
             .wasm32 => return WValue{ .imm32 = 0xaaaaaaaa },
             .wasm64 => return WValue{ .imm64 = 0xaaaaaaaaaaaaaaaa },
             else => unreachable,
         },
         .Optional => {
             const pl_ty = ty.optionalChild(mod);
             if (ty.optionalReprIsPayload(mod)) {
                 return func.emitUndefined(pl_ty);
             }
             return WValue{ .imm32 = 0xaaaaaaaa };
         },
         .ErrorUnion => {
             return WValue{ .imm32 = 0xaaaaaaaa };
         },
         .Struct => {
             const packed_struct = mod.typeToPackedStruct(ty).?;
             return func.emitUndefined(Type.fromInterned(packed_struct.backingIntType(ip).*));
         },
         else => return func.fail("Wasm TODO: emitUndefined for type: {}\n", .{ty.zigTypeTag(mod)}),
     }
 }
 
 /// Returns a `Value` as a signed 32 bit value.
 /// It's illegal to provide a value with a type that cannot be represented
 /// as an integer value.
 fn valueAsI32(func: *const CodeGen, val: Value, ty: Type) i32 {
     const mod = func.bin_file.base.comp.module.?;
 
     switch (val.ip_index) {
         .none => {},
         .bool_true => return 1,
         .bool_false => return 0,
         else => return switch (mod.intern_pool.indexToKey(val.ip_index)) {
             .enum_tag => |enum_tag| intIndexAsI32(&mod.intern_pool, enum_tag.int, mod),
             .int => |int| intStorageAsI32(int.storage, mod),
             .ptr => |ptr| intIndexAsI32(&mod.intern_pool, ptr.addr.int, mod),
             .err => |err| @as(i32, @bitCast(@as(Module.ErrorInt, @intCast(mod.global_error_set.getIndex(err.name).?)))),
             else => unreachable,
         },
     }
 
     return switch (ty.zigTypeTag(mod)) {
         .ErrorSet => @as(i32, @bitCast(val.getErrorInt(mod))),
         else => unreachable, // Programmer called this function for an illegal type
     };
 }
 
 fn intIndexAsI32(ip: *const InternPool, int: InternPool.Index, mod: *Module) i32 {
     return intStorageAsI32(ip.indexToKey(int).int.storage, mod);
 }
 
 fn intStorageAsI32(storage: InternPool.Key.Int.Storage, mod: *Module) i32 {
     return switch (storage) {
         .i64 => |x| @as(i32, @intCast(x)),
         .u64 => |x| @as(i32, @bitCast(@as(u32, @intCast(x)))),
         .big_int => unreachable,
         .lazy_align => |ty| @as(i32, @bitCast(@as(u32, @intCast(Type.fromInterned(ty).abiAlignment(mod).toByteUnits(0))))),
         .lazy_size => |ty| @as(i32, @bitCast(@as(u32, @intCast(Type.fromInterned(ty).abiSize(mod))))),
     };
 }
 
 fn airBlock(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const block_ty = ty_pl.ty.toType();
     const wasm_block_ty = genBlockType(block_ty, mod);
     const extra = func.air.extraData(Air.Block, ty_pl.payload);
     const body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra.end..][0..extra.data.body_len]);
 
     // if wasm_block_ty is non-empty, we create a register to store the temporary value
     const block_result: WValue = if (wasm_block_ty != wasm.block_empty) blk: {
         const ty: Type = if (isByRef(block_ty, mod)) Type.u32 else block_ty;
         break :blk try func.ensureAllocLocal(ty); // make sure it's a clean local as it may never get overwritten
     } else WValue.none;
 
     try func.startBlock(.block, wasm.block_empty);
     // Here we set the current block idx, so breaks know the depth to jump
     // to when breaking out.
     try func.blocks.putNoClobber(func.gpa, inst, .{
         .label = func.block_depth,
         .value = block_result,
     });
 
     try func.genBody(body);
     try func.endBlock();
 
     const liveness = func.liveness.getBlock(inst);
     try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths.len);
 
     func.finishAir(inst, block_result, &.{});
 }
 
 /// appends a new wasm block to the code section and increases the `block_depth` by 1
 fn startBlock(func: *CodeGen, block_tag: wasm.Opcode, valtype: u8) !void {
     func.block_depth += 1;
     try func.addInst(.{
         .tag = Mir.Inst.Tag.fromOpcode(block_tag),
         .data = .{ .block_type = valtype },
     });
 }
 
 /// Ends the current wasm block and decreases the `block_depth` by 1
 fn endBlock(func: *CodeGen) !void {
     try func.addTag(.end);
     func.block_depth -= 1;
 }
 
 fn airLoop(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const loop = func.air.extraData(Air.Block, ty_pl.payload);
     const body: []const Air.Inst.Index = @ptrCast(func.air.extra[loop.end..][0..loop.data.body_len]);
 
     // result type of loop is always 'noreturn', meaning we can always
     // emit the wasm type 'block_empty'.
     try func.startBlock(.loop, wasm.block_empty);
     try func.genBody(body);
 
     // breaking to the index of a loop block will continue the loop instead
     try func.addLabel(.br, 0);
     try func.endBlock();
 
     func.finishAir(inst, .none, &.{});
 }
 
 fn airCondBr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const condition = try func.resolveInst(pl_op.operand);
     const extra = func.air.extraData(Air.CondBr, pl_op.payload);
     const then_body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra.end..][0..extra.data.then_body_len]);
     const else_body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra.end + then_body.len ..][0..extra.data.else_body_len]);
     const liveness_condbr = func.liveness.getCondBr(inst);
 
     // result type is always noreturn, so use `block_empty` as type.
     try func.startBlock(.block, wasm.block_empty);
     // emit the conditional value
     try func.emitWValue(condition);
 
     // we inserted the block in front of the condition
     // so now check if condition matches. If not, break outside this block
     // and continue with the then codepath
     try func.addLabel(.br_if, 0);
 
     try func.branches.ensureUnusedCapacity(func.gpa, 2);
     {
         func.branches.appendAssumeCapacity(.{});
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @as(u32, @intCast(liveness_condbr.else_deaths.len)));
         defer {
             var else_stack = func.branches.pop();
             else_stack.deinit(func.gpa);
         }
         try func.genBody(else_body);
         try func.endBlock();
     }
 
     // Outer block that matches the condition
     {
         func.branches.appendAssumeCapacity(.{});
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @as(u32, @intCast(liveness_condbr.then_deaths.len)));
         defer {
             var then_stack = func.branches.pop();
             then_stack.deinit(func.gpa);
         }
         try func.genBody(then_body);
     }
 
     func.finishAir(inst, .none, &.{});
 }
 
 fn airCmp(func: *CodeGen, inst: Air.Inst.Index, op: std.math.CompareOperator) InnerError!void {
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const operand_ty = func.typeOf(bin_op.lhs);
     const result = try (try func.cmp(lhs, rhs, operand_ty, op)).toLocal(func, Type.u32); // comparison result is always 32 bits
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Compares two operands.
 /// Asserts rhs is not a stack value when the lhs isn't a stack value either
 /// NOTE: This leaves the result on top of the stack, rather than a new local.
 fn cmp(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, op: std.math.CompareOperator) InnerError!WValue {
     assert(!(lhs != .stack and rhs == .stack));
     const mod = func.bin_file.base.comp.module.?;
     if (ty.zigTypeTag(mod) == .Optional and !ty.optionalReprIsPayload(mod)) {
         const payload_ty = ty.optionalChild(mod);
         if (payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             // When we hit this case, we must check the value of optionals
             // that are not pointers. This means first checking against non-null for
             // both lhs and rhs, as well as checking the payload are matching of lhs and rhs
             return func.cmpOptionals(lhs, rhs, ty, op);
         }
     } else if (ty.isAnyFloat()) {
         return func.cmpFloat(ty, lhs, rhs, op);
     } else if (isByRef(ty, mod)) {
         return func.cmpBigInt(lhs, rhs, ty, op);
     }
 
     const signedness: std.builtin.Signedness = blk: {
         // by default we tell the operand type is unsigned (i.e. bools and enum values)
         if (ty.zigTypeTag(mod) != .Int) break :blk .unsigned;
 
         // incase of an actual integer, we emit the correct signedness
         break :blk ty.intInfo(mod).signedness;
     };
     const extend_sign = blk: {
         // do we need to extend the sign bit?
         if (signedness != .signed) break :blk false;
         if (op == .eq or op == .neq) break :blk false;
         const int_bits = ty.intInfo(mod).bits;
         const wasm_bits = toWasmBits(int_bits) orelse unreachable;
         break :blk (wasm_bits != int_bits);
     };
 
     const lhs_wasm = if (extend_sign)
         try func.signExtendInt(lhs, ty)
     else
         lhs;
 
     const rhs_wasm = if (extend_sign)
         try func.signExtendInt(rhs, ty)
     else
         rhs;
 
     // ensure that when we compare pointers, we emit
     // the true pointer of a stack value, rather than the stack pointer.
     try func.lowerToStack(lhs_wasm);
     try func.lowerToStack(rhs_wasm);
 
     const opcode: wasm.Opcode = buildOpcode(.{
         .valtype1 = typeToValtype(ty, mod),
         .op = switch (op) {
             .lt => .lt,
             .lte => .le,
             .eq => .eq,
             .neq => .ne,
             .gte => .ge,
             .gt => .gt,
         },
         .signedness = signedness,
     });
     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
 
     return WValue{ .stack = {} };
 }
 
 /// Compares two floats.
 /// NOTE: Leaves the result of the comparison on top of the stack.
 fn cmpFloat(func: *CodeGen, ty: Type, lhs: WValue, rhs: WValue, cmp_op: std.math.CompareOperator) InnerError!WValue {
     const float_bits = ty.floatBits(func.target);
 
     const op: Op = switch (cmp_op) {
         .lt => .lt,
         .lte => .le,
         .eq => .eq,
         .neq => .ne,
         .gte => .ge,
         .gt => .gt,
     };
 
     switch (float_bits) {
         16 => {
             _ = try func.fpext(lhs, Type.f16, Type.f32);
             _ = try func.fpext(rhs, Type.f16, Type.f32);
             const opcode = buildOpcode(.{ .op = op, .valtype1 = .f32 });
             try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
             return .stack;
         },
         32, 64 => {
             try func.emitWValue(lhs);
             try func.emitWValue(rhs);
             const val_type: wasm.Valtype = if (float_bits == 32) .f32 else .f64;
             const opcode = buildOpcode(.{ .op = op, .valtype1 = val_type });
             try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
             return .stack;
         },
         80, 128 => {
             var fn_name_buf: [32]u8 = undefined;
             const fn_name = std.fmt.bufPrint(&fn_name_buf, "__{s}{s}f2", .{
                 @tagName(op), target_util.compilerRtFloatAbbrev(float_bits),
             }) catch unreachable;
 
             const result = try func.callIntrinsic(fn_name, &.{ ty.ip_index, ty.ip_index }, Type.bool, &.{ lhs, rhs });
             return func.cmp(result, WValue{ .imm32 = 0 }, Type.i32, cmp_op);
         },
         else => unreachable,
     }
 }
 
 fn airCmpVector(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     _ = inst;
     return func.fail("TODO implement airCmpVector for wasm", .{});
 }
 
 fn airCmpLtErrorsLen(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const sym_index = try func.bin_file.getGlobalSymbol("__zig_errors_len", null);
     const errors_len = WValue{ .memory = sym_index };
 
     try func.emitWValue(operand);
     const mod = func.bin_file.base.comp.module.?;
     const err_int_ty = try mod.errorIntType();
     const errors_len_val = try func.load(errors_len, err_int_ty, 0);
     const result = try func.cmp(.stack, errors_len_val, err_int_ty, .lt);
 
     return func.finishAir(inst, try result.toLocal(func, Type.bool), &.{un_op});
 }
 
 fn airBr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const br = func.air.instructions.items(.data)[@intFromEnum(inst)].br;
     const block = func.blocks.get(br.block_inst).?;
 
     // if operand has codegen bits we should break with a value
     if (func.typeOf(br.operand).hasRuntimeBitsIgnoreComptime(mod)) {
         const operand = try func.resolveInst(br.operand);
         try func.lowerToStack(operand);
 
         if (block.value != .none) {
             try func.addLabel(.local_set, block.value.local.value);
         }
     }
 
     // We map every block to its block index.
     // We then determine how far we have to jump to it by subtracting it from current block depth
     const idx: u32 = func.block_depth - block.label;
     try func.addLabel(.br, idx);
 
     func.finishAir(inst, .none, &.{br.operand});
 }
 
 fn airNot(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const operand_ty = func.typeOf(ty_op.operand);
     const mod = func.bin_file.base.comp.module.?;
 
     const result = result: {
         if (operand_ty.zigTypeTag(mod) == .Bool) {
             try func.emitWValue(operand);
             try func.addTag(.i32_eqz);
             const not_tmp = try func.allocLocal(operand_ty);
             try func.addLabel(.local_set, not_tmp.local.value);
             break :result not_tmp;
         } else {
             const operand_bits = operand_ty.intInfo(mod).bits;
             const wasm_bits = toWasmBits(operand_bits) orelse {
                 return func.fail("TODO: Implement binary NOT for integer with bitsize '{d}'", .{operand_bits});
             };
 
             switch (wasm_bits) {
                 32 => {
                     const bin_op = try func.binOp(operand, .{ .imm32 = ~@as(u32, 0) }, operand_ty, .xor);
                     break :result try (try func.wrapOperand(bin_op, operand_ty)).toLocal(func, operand_ty);
                 },
                 64 => {
                     const bin_op = try func.binOp(operand, .{ .imm64 = ~@as(u64, 0) }, operand_ty, .xor);
                     break :result try (try func.wrapOperand(bin_op, operand_ty)).toLocal(func, operand_ty);
                 },
                 128 => {
                     const result_ptr = try func.allocStack(operand_ty);
                     try func.emitWValue(result_ptr);
                     const msb = try func.load(operand, Type.u64, 0);
                     const msb_xor = try func.binOp(msb, .{ .imm64 = ~@as(u64, 0) }, Type.u64, .xor);
                     try func.store(.{ .stack = {} }, msb_xor, Type.u64, 0 + result_ptr.offset());
 
                     try func.emitWValue(result_ptr);
                     const lsb = try func.load(operand, Type.u64, 8);
                     const lsb_xor = try func.binOp(lsb, .{ .imm64 = ~@as(u64, 0) }, Type.u64, .xor);
                     try func.store(result_ptr, lsb_xor, Type.u64, 8 + result_ptr.offset());
                     break :result result_ptr;
                 },
                 else => unreachable,
             }
         }
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airTrap(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     try func.addTag(.@"unreachable");
     func.finishAir(inst, .none, &.{});
 }
 
 fn airBreakpoint(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     // unsupported by wasm itfunc. Can be implemented once we support DWARF
     // for wasm
     try func.addTag(.@"unreachable");
     func.finishAir(inst, .none, &.{});
 }
 
 fn airUnreachable(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     try func.addTag(.@"unreachable");
     func.finishAir(inst, .none, &.{});
 }
 
 fn airBitcast(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const result = result: {
         const operand = try func.resolveInst(ty_op.operand);
         const wanted_ty = func.typeOfIndex(inst);
         const given_ty = func.typeOf(ty_op.operand);
         if (given_ty.isAnyFloat() or wanted_ty.isAnyFloat()) {
             const bitcast_result = try func.bitcast(wanted_ty, given_ty, operand);
             break :result try bitcast_result.toLocal(func, wanted_ty);
         }
         const mod = func.bin_file.base.comp.module.?;
         if (isByRef(given_ty, mod) and !isByRef(wanted_ty, mod)) {
             const loaded_memory = try func.load(operand, wanted_ty, 0);
             break :result try loaded_memory.toLocal(func, wanted_ty);
         }
         if (!isByRef(given_ty, mod) and isByRef(wanted_ty, mod)) {
             const stack_memory = try func.allocStack(wanted_ty);
             try func.store(stack_memory, operand, given_ty, 0);
             break :result stack_memory;
         }
         break :result func.reuseOperand(ty_op.operand, operand);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn bitcast(func: *CodeGen, wanted_ty: Type, given_ty: Type, operand: WValue) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     // if we bitcast a float to or from an integer we must use the 'reinterpret' instruction
     if (!(wanted_ty.isAnyFloat() or given_ty.isAnyFloat())) return operand;
     if (wanted_ty.ip_index == .f16_type or given_ty.ip_index == .f16_type) return operand;
     if (wanted_ty.bitSize(mod) > 64) return operand;
     assert((wanted_ty.isInt(mod) and given_ty.isAnyFloat()) or (wanted_ty.isAnyFloat() and given_ty.isInt(mod)));
 
     const opcode = buildOpcode(.{
         .op = .reinterpret,
         .valtype1 = typeToValtype(wanted_ty, mod),
         .valtype2 = typeToValtype(given_ty, mod),
     });
     try func.emitWValue(operand);
     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
     return WValue{ .stack = {} };
 }
 
 fn airStructFieldPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.StructField, ty_pl.payload);
 
     const struct_ptr = try func.resolveInst(extra.data.struct_operand);
     const struct_ptr_ty = func.typeOf(extra.data.struct_operand);
     const struct_ty = struct_ptr_ty.childType(mod);
     const result = try func.structFieldPtr(inst, extra.data.struct_operand, struct_ptr, struct_ptr_ty, struct_ty, extra.data.field_index);
     func.finishAir(inst, result, &.{extra.data.struct_operand});
 }
 
 fn airStructFieldPtrIndex(func: *CodeGen, inst: Air.Inst.Index, index: u32) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const struct_ptr = try func.resolveInst(ty_op.operand);
     const struct_ptr_ty = func.typeOf(ty_op.operand);
     const struct_ty = struct_ptr_ty.childType(mod);
 
     const result = try func.structFieldPtr(inst, ty_op.operand, struct_ptr, struct_ptr_ty, struct_ty, index);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn structFieldPtr(
     func: *CodeGen,
     inst: Air.Inst.Index,
     ref: Air.Inst.Ref,
     struct_ptr: WValue,
     struct_ptr_ty: Type,
     struct_ty: Type,
     index: u32,
 ) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const result_ty = func.typeOfIndex(inst);
     const struct_ptr_ty_info = struct_ptr_ty.ptrInfo(mod);
 
     const offset = switch (struct_ty.containerLayout(mod)) {
         .Packed => switch (struct_ty.zigTypeTag(mod)) {
             .Struct => offset: {
                 if (result_ty.ptrInfo(mod).packed_offset.host_size != 0) {
                     break :offset @as(u32, 0);
                 }
                 const struct_type = mod.typeToStruct(struct_ty).?;
                 break :offset @divExact(mod.structPackedFieldBitOffset(struct_type, index) + struct_ptr_ty_info.packed_offset.bit_offset, 8);
             },
             .Union => 0,
             else => unreachable,
         },
         else => struct_ty.structFieldOffset(index, mod),
     };
     // save a load and store when we can simply reuse the operand
     if (offset == 0) {
         return func.reuseOperand(ref, struct_ptr);
     }
     switch (struct_ptr) {
         .stack_offset => |stack_offset| {
             return WValue{ .stack_offset = .{ .value = stack_offset.value + @as(u32, @intCast(offset)), .references = 1 } };
         },
         else => return func.buildPointerOffset(struct_ptr, offset, .new),
     }
 }
 
 fn airStructFieldVal(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const struct_field = func.air.extraData(Air.StructField, ty_pl.payload).data;
 
     const struct_ty = func.typeOf(struct_field.struct_operand);
     const operand = try func.resolveInst(struct_field.struct_operand);
     const field_index = struct_field.field_index;
     const field_ty = struct_ty.structFieldType(field_index, mod);
     if (!field_ty.hasRuntimeBitsIgnoreComptime(mod)) return func.finishAir(inst, .none, &.{struct_field.struct_operand});
 
     const result = switch (struct_ty.containerLayout(mod)) {
         .Packed => switch (struct_ty.zigTypeTag(mod)) {
             .Struct => result: {
                 const packed_struct = mod.typeToPackedStruct(struct_ty).?;
                 const offset = mod.structPackedFieldBitOffset(packed_struct, field_index);
                 const backing_ty = Type.fromInterned(packed_struct.backingIntType(ip).*);
                 const wasm_bits = toWasmBits(backing_ty.intInfo(mod).bits) orelse {
                     return func.fail("TODO: airStructFieldVal for packed structs larger than 128 bits", .{});
                 };
                 const const_wvalue = if (wasm_bits == 32)
                     WValue{ .imm32 = offset }
                 else if (wasm_bits == 64)
                     WValue{ .imm64 = offset }
                 else
                     return func.fail("TODO: airStructFieldVal for packed structs larger than 64 bits", .{});
 
                 // for first field we don't require any shifting
                 const shifted_value = if (offset == 0)
                     operand
                 else
                     try func.binOp(operand, const_wvalue, backing_ty, .shr);
 
                 if (field_ty.zigTypeTag(mod) == .Float) {
                     const int_type = try mod.intType(.unsigned, @as(u16, @intCast(field_ty.bitSize(mod))));
                     const truncated = try func.trunc(shifted_value, int_type, backing_ty);
                     const bitcasted = try func.bitcast(field_ty, int_type, truncated);
                     break :result try bitcasted.toLocal(func, field_ty);
                 } else if (field_ty.isPtrAtRuntime(mod) and packed_struct.field_types.len == 1) {
                     // In this case we do not have to perform any transformations,
                     // we can simply reuse the operand.
                     break :result func.reuseOperand(struct_field.struct_operand, operand);
                 } else if (field_ty.isPtrAtRuntime(mod)) {
                     const int_type = try mod.intType(.unsigned, @as(u16, @intCast(field_ty.bitSize(mod))));
                     const truncated = try func.trunc(shifted_value, int_type, backing_ty);
                     break :result try truncated.toLocal(func, field_ty);
                 }
                 const truncated = try func.trunc(shifted_value, field_ty, backing_ty);
                 break :result try truncated.toLocal(func, field_ty);
             },
             .Union => result: {
                 if (isByRef(struct_ty, mod)) {
                     if (!isByRef(field_ty, mod)) {
                         const val = try func.load(operand, field_ty, 0);
                         break :result try val.toLocal(func, field_ty);
                     } else {
                         const new_stack_val = try func.allocStack(field_ty);
                         try func.store(new_stack_val, operand, field_ty, 0);
                         break :result new_stack_val;
                     }
                 }
 
                 const union_int_type = try mod.intType(.unsigned, @as(u16, @intCast(struct_ty.bitSize(mod))));
                 if (field_ty.zigTypeTag(mod) == .Float) {
                     const int_type = try mod.intType(.unsigned, @as(u16, @intCast(field_ty.bitSize(mod))));
                     const truncated = try func.trunc(operand, int_type, union_int_type);
                     const bitcasted = try func.bitcast(field_ty, int_type, truncated);
                     break :result try bitcasted.toLocal(func, field_ty);
                 } else if (field_ty.isPtrAtRuntime(mod)) {
                     const int_type = try mod.intType(.unsigned, @as(u16, @intCast(field_ty.bitSize(mod))));
                     const truncated = try func.trunc(operand, int_type, union_int_type);
                     break :result try truncated.toLocal(func, field_ty);
                 }
                 const truncated = try func.trunc(operand, field_ty, union_int_type);
                 break :result try truncated.toLocal(func, field_ty);
             },
             else => unreachable,
         },
         else => result: {
             const offset = std.math.cast(u32, struct_ty.structFieldOffset(field_index, mod)) orelse {
                 return func.fail("Field type '{}' too big to fit into stack frame", .{field_ty.fmt(mod)});
             };
             if (isByRef(field_ty, mod)) {
                 switch (operand) {
                     .stack_offset => |stack_offset| {
                         break :result WValue{ .stack_offset = .{ .value = stack_offset.value + offset, .references = 1 } };
                     },
                     else => break :result try func.buildPointerOffset(operand, offset, .new),
                 }
             }
             const field = try func.load(operand, field_ty, offset);
             break :result try field.toLocal(func, field_ty);
         },
     };
 
     func.finishAir(inst, result, &.{struct_field.struct_operand});
 }
 
 fn airSwitchBr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     // result type is always 'noreturn'
     const blocktype = wasm.block_empty;
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const target = try func.resolveInst(pl_op.operand);
     const target_ty = func.typeOf(pl_op.operand);
     const switch_br = func.air.extraData(Air.SwitchBr, pl_op.payload);
     const liveness = try func.liveness.getSwitchBr(func.gpa, inst, switch_br.data.cases_len + 1);
     defer func.gpa.free(liveness.deaths);
 
     var extra_index: usize = switch_br.end;
     var case_i: u32 = 0;
 
     // a list that maps each value with its value and body based on the order inside the list.
     const CaseValue = struct { integer: i32, value: Value };
     var case_list = try std.ArrayList(struct {
         values: []const CaseValue,
         body: []const Air.Inst.Index,
     }).initCapacity(func.gpa, switch_br.data.cases_len);
     defer for (case_list.items) |case| {
         func.gpa.free(case.values);
     } else case_list.deinit();
 
     var lowest_maybe: ?i32 = null;
     var highest_maybe: ?i32 = null;
     while (case_i < switch_br.data.cases_len) : (case_i += 1) {
         const case = func.air.extraData(Air.SwitchBr.Case, extra_index);
         const items: []const Air.Inst.Ref = @ptrCast(func.air.extra[case.end..][0..case.data.items_len]);
         const case_body: []const Air.Inst.Index = @ptrCast(func.air.extra[case.end + items.len ..][0..case.data.body_len]);
         extra_index = case.end + items.len + case_body.len;
         const values = try func.gpa.alloc(CaseValue, items.len);
         errdefer func.gpa.free(values);
 
         for (items, 0..) |ref, i| {
             const item_val = (try func.air.value(ref, mod)).?;
             const int_val = func.valueAsI32(item_val, target_ty);
             if (lowest_maybe == null or int_val < lowest_maybe.?) {
                 lowest_maybe = int_val;
             }
             if (highest_maybe == null or int_val > highest_maybe.?) {
                 highest_maybe = int_val;
             }
             values[i] = .{ .integer = int_val, .value = item_val };
         }
 
         case_list.appendAssumeCapacity(.{ .values = values, .body = case_body });
         try func.startBlock(.block, blocktype);
     }
 
     // When highest and lowest are null, we have no cases and can use a jump table
     const lowest = lowest_maybe orelse 0;
     const highest = highest_maybe orelse 0;
     // When the highest and lowest values are seperated by '50',
     // we define it as sparse and use an if/else-chain, rather than a jump table.
     // When the target is an integer size larger than u32, we have no way to use the value
     // as an index, therefore we also use an if/else-chain for those cases.
     // TODO: Benchmark this to find a proper value, LLVM seems to draw the line at '40~45'.
     const is_sparse = highest - lowest > 50 or target_ty.bitSize(mod) > 32;
 
     const else_body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra_index..][0..switch_br.data.else_body_len]);
     const has_else_body = else_body.len != 0;
     if (has_else_body) {
         try func.startBlock(.block, blocktype);
     }
 
     if (!is_sparse) {
         // Generate the jump table 'br_table' when the prongs are not sparse.
         // The value 'target' represents the index into the table.
         // Each index in the table represents a label to the branch
         // to jump to.
         try func.startBlock(.block, blocktype);
         try func.emitWValue(target);
         if (lowest < 0) {
             // since br_table works using indexes, starting from '0', we must ensure all values
             // we put inside, are atleast 0.
             try func.addImm32(lowest * -1);
             try func.addTag(.i32_add);
         } else if (lowest > 0) {
             // make the index start from 0 by substracting the lowest value
             try func.addImm32(lowest);
             try func.addTag(.i32_sub);
         }
 
         // Account for default branch so always add '1'
         const depth = @as(u32, @intCast(highest - lowest + @intFromBool(has_else_body))) + 1;
         const jump_table: Mir.JumpTable = .{ .length = depth };
         const table_extra_index = try func.addExtra(jump_table);
         try func.addInst(.{ .tag = .br_table, .data = .{ .payload = table_extra_index } });
         try func.mir_extra.ensureUnusedCapacity(func.gpa, depth);
         var value = lowest;
         while (value <= highest) : (value += 1) {
             // idx represents the branch we jump to
             const idx = blk: {
                 for (case_list.items, 0..) |case, idx| {
                     for (case.values) |case_value| {
                         if (case_value.integer == value) break :blk @as(u32, @intCast(idx));
                     }
                 }
                 // error sets are almost always sparse so we use the default case
                 // for errors that are not present in any branch. This is fine as this default
                 // case will never be hit for those cases but we do save runtime cost and size
                 // by using a jump table for this instead of if-else chains.
                 break :blk if (has_else_body or target_ty.zigTypeTag(mod) == .ErrorSet) case_i else unreachable;
             };
             func.mir_extra.appendAssumeCapacity(idx);
         } else if (has_else_body) {
             func.mir_extra.appendAssumeCapacity(case_i); // default branch
         }
         try func.endBlock();
     }
 
     const signedness: std.builtin.Signedness = blk: {
         // by default we tell the operand type is unsigned (i.e. bools and enum values)
         if (target_ty.zigTypeTag(mod) != .Int) break :blk .unsigned;
 
         // incase of an actual integer, we emit the correct signedness
         break :blk target_ty.intInfo(mod).signedness;
     };
 
     try func.branches.ensureUnusedCapacity(func.gpa, case_list.items.len + @intFromBool(has_else_body));
     for (case_list.items, 0..) |case, index| {
         // when sparse, we use if/else-chain, so emit conditional checks
         if (is_sparse) {
             // for single value prong we can emit a simple if
             if (case.values.len == 1) {
                 try func.emitWValue(target);
                 const val = try func.lowerConstant(case.values[0].value, target_ty);
                 try func.emitWValue(val);
                 const opcode = buildOpcode(.{
                     .valtype1 = typeToValtype(target_ty, mod),
                     .op = .ne, // not equal, because we want to jump out of this block if it does not match the condition.
                     .signedness = signedness,
                 });
                 try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
                 try func.addLabel(.br_if, 0);
             } else {
                 // in multi-value prongs we must check if any prongs match the target value.
                 try func.startBlock(.block, blocktype);
                 for (case.values) |value| {
                     try func.emitWValue(target);
                     const val = try func.lowerConstant(value.value, target_ty);
                     try func.emitWValue(val);
                     const opcode = buildOpcode(.{
                         .valtype1 = typeToValtype(target_ty, mod),
                         .op = .eq,
                         .signedness = signedness,
                     });
                     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
                     try func.addLabel(.br_if, 0);
                 }
                 // value did not match any of the prong values
                 try func.addLabel(.br, 1);
                 try func.endBlock();
             }
         }
         func.branches.appendAssumeCapacity(.{});
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths[index].len);
         defer {
             var case_branch = func.branches.pop();
             case_branch.deinit(func.gpa);
         }
         try func.genBody(case.body);
         try func.endBlock();
     }
 
     if (has_else_body) {
         func.branches.appendAssumeCapacity(.{});
         const else_deaths = liveness.deaths.len - 1;
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths[else_deaths].len);
         defer {
             var else_branch = func.branches.pop();
             else_branch.deinit(func.gpa);
         }
         try func.genBody(else_body);
         try func.endBlock();
     }
     func.finishAir(inst, .none, &.{});
 }
 
 fn airIsErr(func: *CodeGen, inst: Air.Inst.Index, opcode: wasm.Opcode) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const err_union_ty = func.typeOf(un_op);
     const pl_ty = err_union_ty.errorUnionPayload(mod);
 
     const result = result: {
         if (err_union_ty.errorUnionSet(mod).errorSetIsEmpty(mod)) {
             switch (opcode) {
                 .i32_ne => break :result WValue{ .imm32 = 0 },
                 .i32_eq => break :result WValue{ .imm32 = 1 },
                 else => unreachable,
             }
         }
 
         try func.emitWValue(operand);
         if (pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             try func.addMemArg(.i32_load16_u, .{
                 .offset = operand.offset() + @as(u32, @intCast(errUnionErrorOffset(pl_ty, mod))),
                 .alignment = @intCast(Type.anyerror.abiAlignment(mod).toByteUnitsOptional().?),
             });
         }
 
         // Compare the error value with '0'
         try func.addImm32(0);
         try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
 
         const is_err_tmp = try func.allocLocal(Type.i32);
         try func.addLabel(.local_set, is_err_tmp.local.value);
         break :result is_err_tmp;
     };
     func.finishAir(inst, result, &.{un_op});
 }
 
 fn airUnwrapErrUnionPayload(func: *CodeGen, inst: Air.Inst.Index, op_is_ptr: bool) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const op_ty = func.typeOf(ty_op.operand);
     const err_ty = if (op_is_ptr) op_ty.childType(mod) else op_ty;
     const payload_ty = err_ty.errorUnionPayload(mod);
 
     const result = result: {
         if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             if (op_is_ptr) {
                 break :result func.reuseOperand(ty_op.operand, operand);
             }
             break :result WValue{ .none = {} };
         }
 
         const pl_offset = @as(u32, @intCast(errUnionPayloadOffset(payload_ty, mod)));
         if (op_is_ptr or isByRef(payload_ty, mod)) {
             break :result try func.buildPointerOffset(operand, pl_offset, .new);
         }
 
         const payload = try func.load(operand, payload_ty, pl_offset);
         break :result try payload.toLocal(func, payload_ty);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airUnwrapErrUnionError(func: *CodeGen, inst: Air.Inst.Index, op_is_ptr: bool) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const op_ty = func.typeOf(ty_op.operand);
     const err_ty = if (op_is_ptr) op_ty.childType(mod) else op_ty;
     const payload_ty = err_ty.errorUnionPayload(mod);
 
     const result = result: {
         if (err_ty.errorUnionSet(mod).errorSetIsEmpty(mod)) {
             break :result WValue{ .imm32 = 0 };
         }
 
         if (op_is_ptr or !payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
 
         const error_val = try func.load(operand, Type.anyerror, @as(u32, @intCast(errUnionErrorOffset(payload_ty, mod))));
         break :result try error_val.toLocal(func, Type.anyerror);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airWrapErrUnionPayload(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const err_ty = func.typeOfIndex(inst);
 
     const pl_ty = func.typeOf(ty_op.operand);
     const result = result: {
         if (!pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
 
         const err_union = try func.allocStack(err_ty);
         const payload_ptr = try func.buildPointerOffset(err_union, @as(u32, @intCast(errUnionPayloadOffset(pl_ty, mod))), .new);
         try func.store(payload_ptr, operand, pl_ty, 0);
 
         // ensure we also write '0' to the error part, so any present stack value gets overwritten by it.
         try func.emitWValue(err_union);
         try func.addImm32(0);
         const err_val_offset = @as(u32, @intCast(errUnionErrorOffset(pl_ty, mod)));
         try func.addMemArg(.i32_store16, .{
             .offset = err_union.offset() + err_val_offset,
             .alignment = 2,
         });
         break :result err_union;
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airWrapErrUnionErr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const err_ty = ty_op.ty.toType();
     const pl_ty = err_ty.errorUnionPayload(mod);
 
     const result = result: {
         if (!pl_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
 
         const err_union = try func.allocStack(err_ty);
         // store error value
         try func.store(err_union, operand, Type.anyerror, @as(u32, @intCast(errUnionErrorOffset(pl_ty, mod))));
 
         // write 'undefined' to the payload
         const payload_ptr = try func.buildPointerOffset(err_union, @as(u32, @intCast(errUnionPayloadOffset(pl_ty, mod))), .new);
         const len = @as(u32, @intCast(err_ty.errorUnionPayload(mod).abiSize(mod)));
         try func.memset(Type.u8, payload_ptr, .{ .imm32 = len }, .{ .imm32 = 0xaa });
 
         break :result err_union;
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airIntcast(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const ty = ty_op.ty.toType();
     const operand = try func.resolveInst(ty_op.operand);
     const operand_ty = func.typeOf(ty_op.operand);
     const mod = func.bin_file.base.comp.module.?;
     if (ty.zigTypeTag(mod) == .Vector or operand_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("todo Wasm intcast for vectors", .{});
     }
     if (ty.abiSize(mod) > 16 or operand_ty.abiSize(mod) > 16) {
         return func.fail("todo Wasm intcast for bitsize > 128", .{});
     }
 
     const op_bits = toWasmBits(@as(u16, @intCast(operand_ty.bitSize(mod)))).?;
     const wanted_bits = toWasmBits(@as(u16, @intCast(ty.bitSize(mod)))).?;
     const result = if (op_bits == wanted_bits and !ty.isSignedInt(mod))
         func.reuseOperand(ty_op.operand, operand)
     else
         try (try func.intcast(operand, operand_ty, ty)).toLocal(func, ty);
 
     func.finishAir(inst, result, &.{});
 }
 
 /// Upcasts or downcasts an integer based on the given and wanted types,
 /// and stores the result in a new operand.
 /// Asserts type's bitsize <= 128
 /// NOTE: May leave the result on the top of the stack.
 fn intcast(func: *CodeGen, operand: WValue, given: Type, wanted: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const given_bitsize = @as(u16, @intCast(given.bitSize(mod)));
     const wanted_bitsize = @as(u16, @intCast(wanted.bitSize(mod)));
     assert(given_bitsize <= 128);
     assert(wanted_bitsize <= 128);
 
     const op_bits = toWasmBits(given_bitsize).?;
     const wanted_bits = toWasmBits(wanted_bitsize).?;
     if (op_bits == wanted_bits) {
         if (given.isSignedInt(mod)) {
             if (given_bitsize < wanted_bitsize) {
                 // signed integers are stored as two's complement,
                 // when we upcast from a smaller integer to larger
                 // integers, we must get its absolute value similar to
                 // i64_extend_i32_s instruction.
                 return func.signExtendInt(operand, given);
             }
             return func.wrapOperand(operand, wanted);
         }
         return operand;
     }
 
     if (op_bits > 32 and op_bits <= 64 and wanted_bits == 32) {
         try func.emitWValue(operand);
         try func.addTag(.i32_wrap_i64);
         if (given.isSignedInt(mod) and wanted_bitsize < 32)
             return func.wrapOperand(.{ .stack = {} }, wanted)
         else
             return WValue{ .stack = {} };
     } else if (op_bits == 32 and wanted_bits > 32 and wanted_bits <= 64) {
         const operand32 = if (given_bitsize < 32 and wanted.isSignedInt(mod))
             try func.signExtendInt(operand, given)
         else
             operand;
         try func.emitWValue(operand32);
         try func.addTag(if (wanted.isSignedInt(mod)) .i64_extend_i32_s else .i64_extend_i32_u);
         if (given.isSignedInt(mod) and wanted_bitsize < 64)
             return func.wrapOperand(.{ .stack = {} }, wanted)
         else
             return WValue{ .stack = {} };
     } else if (wanted_bits == 128) {
         // for 128bit integers we store the integer in the virtual stack, rather than a local
         const stack_ptr = try func.allocStack(wanted);
         try func.emitWValue(stack_ptr);
 
         // for 32 bit integers, we first coerce the value into a 64 bit integer before storing it
         // meaning less store operations are required.
         const lhs = if (op_bits == 32) blk: {
             break :blk try func.intcast(operand, given, if (wanted.isSignedInt(mod)) Type.i64 else Type.u64);
         } else operand;
 
         // store msb first
         try func.store(.{ .stack = {} }, lhs, Type.u64, 0 + stack_ptr.offset());
 
         // For signed integers we shift msb by 63 (64bit integer - 1 sign bit) and store remaining value
         if (wanted.isSignedInt(mod)) {
             try func.emitWValue(stack_ptr);
             const shr = try func.binOp(lhs, .{ .imm64 = 63 }, Type.i64, .shr);
             try func.store(.{ .stack = {} }, shr, Type.u64, 8 + stack_ptr.offset());
         } else {
             // Ensure memory of lsb is zero'd
             try func.store(stack_ptr, .{ .imm64 = 0 }, Type.u64, 8);
         }
         return stack_ptr;
     } else return func.load(operand, wanted, 0);
 }
 
 fn airIsNull(func: *CodeGen, inst: Air.Inst.Index, opcode: wasm.Opcode, op_kind: enum { value, ptr }) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
 
     const op_ty = func.typeOf(un_op);
     const optional_ty = if (op_kind == .ptr) op_ty.childType(mod) else op_ty;
     const is_null = try func.isNull(operand, optional_ty, opcode);
     const result = try is_null.toLocal(func, optional_ty);
     func.finishAir(inst, result, &.{un_op});
 }
 
 /// For a given type and operand, checks if it's considered `null`.
 /// NOTE: Leaves the result on the stack
 fn isNull(func: *CodeGen, operand: WValue, optional_ty: Type, opcode: wasm.Opcode) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     try func.emitWValue(operand);
     const payload_ty = optional_ty.optionalChild(mod);
     if (!optional_ty.optionalReprIsPayload(mod)) {
         // When payload is zero-bits, we can treat operand as a value, rather than
         // a pointer to the stack value
         if (payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             const offset = std.math.cast(u32, payload_ty.abiSize(mod)) orelse {
                 return func.fail("Optional type {} too big to fit into stack frame", .{optional_ty.fmt(mod)});
             };
             try func.addMemArg(.i32_load8_u, .{ .offset = operand.offset() + offset, .alignment = 1 });
         }
     } else if (payload_ty.isSlice(mod)) {
         switch (func.arch()) {
             .wasm32 => try func.addMemArg(.i32_load, .{ .offset = operand.offset(), .alignment = 4 }),
             .wasm64 => try func.addMemArg(.i64_load, .{ .offset = operand.offset(), .alignment = 8 }),
             else => unreachable,
         }
     }
 
     // Compare the null value with '0'
     try func.addImm32(0);
     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
 
     return WValue{ .stack = {} };
 }
 
 fn airOptionalPayload(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const opt_ty = func.typeOf(ty_op.operand);
     const payload_ty = func.typeOfIndex(inst);
     if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         return func.finishAir(inst, .none, &.{ty_op.operand});
     }
 
     const result = result: {
         const operand = try func.resolveInst(ty_op.operand);
         if (opt_ty.optionalReprIsPayload(mod)) break :result func.reuseOperand(ty_op.operand, operand);
 
         if (isByRef(payload_ty, mod)) {
             break :result try func.buildPointerOffset(operand, 0, .new);
         }
 
         const payload = try func.load(operand, payload_ty, 0);
         break :result try payload.toLocal(func, payload_ty);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airOptionalPayloadPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     const opt_ty = func.typeOf(ty_op.operand).childType(mod);
 
     const result = result: {
         const payload_ty = opt_ty.optionalChild(mod);
         if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod) or opt_ty.optionalReprIsPayload(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
 
         break :result try func.buildPointerOffset(operand, 0, .new);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airOptionalPayloadPtrSet(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     const opt_ty = func.typeOf(ty_op.operand).childType(mod);
     const payload_ty = opt_ty.optionalChild(mod);
     if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         return func.fail("TODO: Implement OptionalPayloadPtrSet for optional with zero-sized type {}", .{payload_ty.fmtDebug()});
     }
 
     if (opt_ty.optionalReprIsPayload(mod)) {
         return func.finishAir(inst, operand, &.{ty_op.operand});
     }
 
     const offset = std.math.cast(u32, payload_ty.abiSize(mod)) orelse {
         return func.fail("Optional type {} too big to fit into stack frame", .{opt_ty.fmt(mod)});
     };
 
     try func.emitWValue(operand);
     try func.addImm32(1);
     try func.addMemArg(.i32_store8, .{ .offset = operand.offset() + offset, .alignment = 1 });
 
     const result = try func.buildPointerOffset(operand, 0, .new);
     return func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airWrapOptional(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const payload_ty = func.typeOf(ty_op.operand);
     const mod = func.bin_file.base.comp.module.?;
 
     const result = result: {
         if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             const non_null_bit = try func.allocStack(Type.u1);
             try func.emitWValue(non_null_bit);
             try func.addImm32(1);
             try func.addMemArg(.i32_store8, .{ .offset = non_null_bit.offset(), .alignment = 1 });
             break :result non_null_bit;
         }
 
         const operand = try func.resolveInst(ty_op.operand);
         const op_ty = func.typeOfIndex(inst);
         if (op_ty.optionalReprIsPayload(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
         const offset = std.math.cast(u32, payload_ty.abiSize(mod)) orelse {
             return func.fail("Optional type {} too big to fit into stack frame", .{op_ty.fmt(mod)});
         };
 
         // Create optional type, set the non-null bit, and store the operand inside the optional type
         const result_ptr = try func.allocStack(op_ty);
         try func.emitWValue(result_ptr);
         try func.addImm32(1);
         try func.addMemArg(.i32_store8, .{ .offset = result_ptr.offset() + offset, .alignment = 1 });
 
         const payload_ptr = try func.buildPointerOffset(result_ptr, 0, .new);
         try func.store(payload_ptr, operand, payload_ty, 0);
         break :result result_ptr;
     };
 
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airSlice(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const bin_op = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const slice_ty = func.typeOfIndex(inst);
 
     const slice = try func.allocStack(slice_ty);
     try func.store(slice, lhs, Type.usize, 0);
     try func.store(slice, rhs, Type.usize, func.ptrSize());
 
     func.finishAir(inst, slice, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airSliceLen(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     func.finishAir(inst, try func.sliceLen(operand), &.{ty_op.operand});
 }
 
 fn airSliceElemVal(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const slice_ty = func.typeOf(bin_op.lhs);
     const slice = try func.resolveInst(bin_op.lhs);
     const index = try func.resolveInst(bin_op.rhs);
     const elem_ty = slice_ty.childType(mod);
     const elem_size = elem_ty.abiSize(mod);
 
     // load pointer onto stack
     _ = try func.load(slice, Type.usize, 0);
 
     // calculate index into slice
     try func.emitWValue(index);
     try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
     try func.addTag(.i32_mul);
     try func.addTag(.i32_add);
 
     const result_ptr = try func.allocLocal(Type.usize);
     try func.addLabel(.local_set, result_ptr.local.value);
 
     const result = if (!isByRef(elem_ty, mod)) result: {
         const elem_val = try func.load(result_ptr, elem_ty, 0);
         break :result try elem_val.toLocal(func, elem_ty);
     } else result_ptr;
 
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airSliceElemPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const bin_op = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const elem_ty = ty_pl.ty.toType().childType(mod);
     const elem_size = elem_ty.abiSize(mod);
 
     const slice = try func.resolveInst(bin_op.lhs);
     const index = try func.resolveInst(bin_op.rhs);
 
     _ = try func.load(slice, Type.usize, 0);
 
     // calculate index into slice
     try func.emitWValue(index);
     try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
     try func.addTag(.i32_mul);
     try func.addTag(.i32_add);
 
     const result = try func.allocLocal(Type.i32);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airSlicePtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     func.finishAir(inst, try func.slicePtr(operand), &.{ty_op.operand});
 }
 
 fn slicePtr(func: *CodeGen, operand: WValue) InnerError!WValue {
     const ptr = try func.load(operand, Type.usize, 0);
     return ptr.toLocal(func, Type.usize);
 }
 
 fn sliceLen(func: *CodeGen, operand: WValue) InnerError!WValue {
     const len = try func.load(operand, Type.usize, func.ptrSize());
     return len.toLocal(func, Type.usize);
 }
 
 fn airTrunc(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const wanted_ty = ty_op.ty.toType();
     const op_ty = func.typeOf(ty_op.operand);
 
     const result = try func.trunc(operand, wanted_ty, op_ty);
     func.finishAir(inst, try result.toLocal(func, wanted_ty), &.{ty_op.operand});
 }
 
 /// Truncates a given operand to a given type, discarding any overflown bits.
 /// NOTE: Resulting value is left on the stack.
 fn trunc(func: *CodeGen, operand: WValue, wanted_ty: Type, given_ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const given_bits = @as(u16, @intCast(given_ty.bitSize(mod)));
     if (toWasmBits(given_bits) == null) {
         return func.fail("TODO: Implement wasm integer truncation for integer bitsize: {d}", .{given_bits});
     }
 
     var result = try func.intcast(operand, given_ty, wanted_ty);
     const wanted_bits = @as(u16, @intCast(wanted_ty.bitSize(mod)));
     const wasm_bits = toWasmBits(wanted_bits).?;
     if (wasm_bits != wanted_bits) {
         result = try func.wrapOperand(result, wanted_ty);
     }
     return result;
 }
 
 fn airIntFromBool(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const result = func.reuseOperand(un_op, operand);
 
     func.finishAir(inst, result, &.{un_op});
 }
 
 fn airArrayToSlice(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const array_ty = func.typeOf(ty_op.operand).childType(mod);
     const slice_ty = ty_op.ty.toType();
 
     // create a slice on the stack
     const slice_local = try func.allocStack(slice_ty);
 
     // store the array ptr in the slice
     if (array_ty.hasRuntimeBitsIgnoreComptime(mod)) {
         try func.store(slice_local, operand, Type.usize, 0);
     }
 
     // store the length of the array in the slice
     const len = WValue{ .imm32 = @as(u32, @intCast(array_ty.arrayLen(mod))) };
     try func.store(slice_local, len, Type.usize, func.ptrSize());
 
     func.finishAir(inst, slice_local, &.{ty_op.operand});
 }
 
 fn airIntFromPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const ptr_ty = func.typeOf(un_op);
     const result = if (ptr_ty.isSlice(mod))
         try func.slicePtr(operand)
     else switch (operand) {
         // for stack offset, return a pointer to this offset.
         .stack_offset => try func.buildPointerOffset(operand, 0, .new),
         else => func.reuseOperand(un_op, operand),
     };
     func.finishAir(inst, result, &.{un_op});
 }
 
 fn airPtrElemVal(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ptr_ty = func.typeOf(bin_op.lhs);
     const ptr = try func.resolveInst(bin_op.lhs);
     const index = try func.resolveInst(bin_op.rhs);
     const elem_ty = ptr_ty.childType(mod);
     const elem_size = elem_ty.abiSize(mod);
 
     // load pointer onto the stack
     if (ptr_ty.isSlice(mod)) {
         _ = try func.load(ptr, Type.usize, 0);
     } else {
         try func.lowerToStack(ptr);
     }
 
     // calculate index into slice
     try func.emitWValue(index);
     try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
     try func.addTag(.i32_mul);
     try func.addTag(.i32_add);
 
     const elem_result = val: {
         var result = try func.allocLocal(Type.usize);
         try func.addLabel(.local_set, result.local.value);
         if (isByRef(elem_ty, mod)) {
             break :val result;
         }
         defer result.free(func); // only free if it's not returned like above
 
         const elem_val = try func.load(result, elem_ty, 0);
         break :val try elem_val.toLocal(func, elem_ty);
     };
     func.finishAir(inst, elem_result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airPtrElemPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const bin_op = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const ptr_ty = func.typeOf(bin_op.lhs);
     const elem_ty = ty_pl.ty.toType().childType(mod);
     const elem_size = elem_ty.abiSize(mod);
 
     const ptr = try func.resolveInst(bin_op.lhs);
     const index = try func.resolveInst(bin_op.rhs);
 
     // load pointer onto the stack
     if (ptr_ty.isSlice(mod)) {
         _ = try func.load(ptr, Type.usize, 0);
     } else {
         try func.lowerToStack(ptr);
     }
 
     // calculate index into ptr
     try func.emitWValue(index);
     try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
     try func.addTag(.i32_mul);
     try func.addTag(.i32_add);
 
     const result = try func.allocLocal(Type.i32);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airPtrBinOp(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const bin_op = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const ptr = try func.resolveInst(bin_op.lhs);
     const offset = try func.resolveInst(bin_op.rhs);
     const ptr_ty = func.typeOf(bin_op.lhs);
     const pointee_ty = switch (ptr_ty.ptrSize(mod)) {
         .One => ptr_ty.childType(mod).childType(mod), // ptr to array, so get array element type
         else => ptr_ty.childType(mod),
     };
 
     const valtype = typeToValtype(Type.usize, mod);
     const mul_opcode = buildOpcode(.{ .valtype1 = valtype, .op = .mul });
     const bin_opcode = buildOpcode(.{ .valtype1 = valtype, .op = op });
 
     try func.lowerToStack(ptr);
     try func.emitWValue(offset);
     try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(pointee_ty.abiSize(mod))))));
     try func.addTag(Mir.Inst.Tag.fromOpcode(mul_opcode));
     try func.addTag(Mir.Inst.Tag.fromOpcode(bin_opcode));
 
     const result = try func.allocLocal(Type.usize);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airMemset(func: *CodeGen, inst: Air.Inst.Index, safety: bool) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     if (safety) {
         // TODO if the value is undef, write 0xaa bytes to dest
     } else {
         // TODO if the value is undef, don't lower this instruction
     }
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ptr = try func.resolveInst(bin_op.lhs);
     const ptr_ty = func.typeOf(bin_op.lhs);
     const value = try func.resolveInst(bin_op.rhs);
     const len = switch (ptr_ty.ptrSize(mod)) {
         .Slice => try func.sliceLen(ptr),
         .One => @as(WValue, .{ .imm32 = @as(u32, @intCast(ptr_ty.childType(mod).arrayLen(mod))) }),
         .C, .Many => unreachable,
     };
 
     const elem_ty = if (ptr_ty.ptrSize(mod) == .One)
         ptr_ty.childType(mod).childType(mod)
     else
         ptr_ty.childType(mod);
 
     const dst_ptr = try func.sliceOrArrayPtr(ptr, ptr_ty);
     try func.memset(elem_ty, dst_ptr, len, value);
 
     func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Sets a region of memory at `ptr` to the value of `value`
 /// When the user has enabled the bulk_memory feature, we lower
 /// this to wasm's memset instruction. When the feature is not present,
 /// we implement it manually.
 fn memset(func: *CodeGen, elem_ty: Type, ptr: WValue, len: WValue, value: WValue) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const abi_size = @as(u32, @intCast(elem_ty.abiSize(mod)));
 
     // When bulk_memory is enabled, we lower it to wasm's memset instruction.
     // If not, we lower it ourselves.
     if (std.Target.wasm.featureSetHas(func.target.cpu.features, .bulk_memory) and abi_size == 1) {
         try func.lowerToStack(ptr);
         try func.emitWValue(value);
         try func.emitWValue(len);
         try func.addExtended(.memory_fill);
         return;
     }
 
     const final_len = switch (len) {
         .imm32 => |val| WValue{ .imm32 = val * abi_size },
         .imm64 => |val| WValue{ .imm64 = val * abi_size },
         else => if (abi_size != 1) blk: {
             const new_len = try func.ensureAllocLocal(Type.usize);
             try func.emitWValue(len);
             switch (func.arch()) {
                 .wasm32 => {
                     try func.emitWValue(.{ .imm32 = abi_size });
                     try func.addTag(.i32_mul);
                 },
                 .wasm64 => {
                     try func.emitWValue(.{ .imm64 = abi_size });
                     try func.addTag(.i64_mul);
                 },
                 else => unreachable,
             }
             try func.addLabel(.local_set, new_len.local.value);
             break :blk new_len;
         } else len,
     };
 
     var end_ptr = try func.allocLocal(Type.usize);
     defer end_ptr.free(func);
     var new_ptr = try func.buildPointerOffset(ptr, 0, .new);
     defer new_ptr.free(func);
 
     // get the loop conditional: if current pointer address equals final pointer's address
     try func.lowerToStack(ptr);
     try func.emitWValue(final_len);
     switch (func.arch()) {
         .wasm32 => try func.addTag(.i32_add),
         .wasm64 => try func.addTag(.i64_add),
         else => unreachable,
     }
     try func.addLabel(.local_set, end_ptr.local.value);
 
     // outer block to jump to when loop is done
     try func.startBlock(.block, wasm.block_empty);
     try func.startBlock(.loop, wasm.block_empty);
 
     // check for codition for loop end
     try func.emitWValue(new_ptr);
     try func.emitWValue(end_ptr);
     switch (func.arch()) {
         .wasm32 => try func.addTag(.i32_eq),
         .wasm64 => try func.addTag(.i64_eq),
         else => unreachable,
     }
     try func.addLabel(.br_if, 1); // jump out of loop into outer block (finished)
 
     // store the value at the current position of the pointer
     try func.store(new_ptr, value, elem_ty, 0);
 
     // move the pointer to the next element
     try func.emitWValue(new_ptr);
     switch (func.arch()) {
         .wasm32 => {
             try func.emitWValue(.{ .imm32 = abi_size });
             try func.addTag(.i32_add);
         },
         .wasm64 => {
             try func.emitWValue(.{ .imm64 = abi_size });
             try func.addTag(.i64_add);
         },
         else => unreachable,
     }
     try func.addLabel(.local_set, new_ptr.local.value);
 
     // end of loop
     try func.addLabel(.br, 0); // jump to start of loop
     try func.endBlock();
     try func.endBlock();
 }
 
 fn airArrayElemVal(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const array_ty = func.typeOf(bin_op.lhs);
     const array = try func.resolveInst(bin_op.lhs);
     const index = try func.resolveInst(bin_op.rhs);
     const elem_ty = array_ty.childType(mod);
     const elem_size = elem_ty.abiSize(mod);
 
     if (isByRef(array_ty, mod)) {
         try func.lowerToStack(array);
         try func.emitWValue(index);
         try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
         try func.addTag(.i32_mul);
         try func.addTag(.i32_add);
     } else {
         std.debug.assert(array_ty.zigTypeTag(mod) == .Vector);
 
         switch (index) {
             inline .imm32, .imm64 => |lane| {
                 const opcode: wasm.SimdOpcode = switch (elem_ty.bitSize(mod)) {
                     8 => if (elem_ty.isSignedInt(mod)) .i8x16_extract_lane_s else .i8x16_extract_lane_u,
                     16 => if (elem_ty.isSignedInt(mod)) .i16x8_extract_lane_s else .i16x8_extract_lane_u,
                     32 => if (elem_ty.isInt(mod)) .i32x4_extract_lane else .f32x4_extract_lane,
                     64 => if (elem_ty.isInt(mod)) .i64x2_extract_lane else .f64x2_extract_lane,
                     else => unreachable,
                 };
 
                 var operands = [_]u32{ std.wasm.simdOpcode(opcode), @as(u8, @intCast(lane)) };
 
                 try func.emitWValue(array);
 
                 const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
                 try func.mir_extra.appendSlice(func.gpa, &operands);
                 try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
 
                 return func.finishAir(inst, try WValue.toLocal(.stack, func, elem_ty), &.{ bin_op.lhs, bin_op.rhs });
             },
             else => {
                 const stack_vec = try func.allocStack(array_ty);
                 try func.store(stack_vec, array, array_ty, 0);
 
                 // Is a non-unrolled vector (v128)
                 try func.lowerToStack(stack_vec);
                 try func.emitWValue(index);
                 try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(elem_size)))));
                 try func.addTag(.i32_mul);
                 try func.addTag(.i32_add);
             },
         }
     }
 
     const elem_result = val: {
         var result = try func.allocLocal(Type.usize);
         try func.addLabel(.local_set, result.local.value);
 
         if (isByRef(elem_ty, mod)) {
             break :val result;
         }
         defer result.free(func); // only free if no longer needed and not returned like above
 
         const elem_val = try func.load(result, elem_ty, 0);
         break :val try elem_val.toLocal(func, elem_ty);
     };
 
     func.finishAir(inst, elem_result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airIntFromFloat(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const op_ty = func.typeOf(ty_op.operand);
     const op_bits = op_ty.floatBits(func.target);
 
     const dest_ty = func.typeOfIndex(inst);
     const dest_info = dest_ty.intInfo(mod);
 
     if (dest_info.bits > 128) {
         return func.fail("TODO: intFromFloat for integers/floats with bitsize {}", .{dest_info.bits});
     }
 
     if ((op_bits != 32 and op_bits != 64) or dest_info.bits > 64) {
         const dest_bitsize = if (dest_info.bits <= 16) 16 else std.math.ceilPowerOfTwoAssert(u16, dest_info.bits);
 
         var fn_name_buf: [16]u8 = undefined;
         const fn_name = std.fmt.bufPrint(&fn_name_buf, "__fix{s}{s}f{s}i", .{
             switch (dest_info.signedness) {
                 .signed => "",
                 .unsigned => "uns",
             },
             target_util.compilerRtFloatAbbrev(op_bits),
             target_util.compilerRtIntAbbrev(dest_bitsize),
         }) catch unreachable;
 
         const result = try (try func.callIntrinsic(fn_name, &.{op_ty.ip_index}, dest_ty, &.{operand})).toLocal(func, dest_ty);
         return func.finishAir(inst, result, &.{ty_op.operand});
     }
 
     try func.emitWValue(operand);
     const op = buildOpcode(.{
         .op = .trunc,
         .valtype1 = typeToValtype(dest_ty, mod),
         .valtype2 = typeToValtype(op_ty, mod),
         .signedness = dest_info.signedness,
     });
     try func.addTag(Mir.Inst.Tag.fromOpcode(op));
     const wrapped = try func.wrapOperand(.{ .stack = {} }, dest_ty);
     const result = try wrapped.toLocal(func, dest_ty);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airFloatFromInt(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const op_ty = func.typeOf(ty_op.operand);
     const op_info = op_ty.intInfo(mod);
 
     const dest_ty = func.typeOfIndex(inst);
     const dest_bits = dest_ty.floatBits(func.target);
 
     if (op_info.bits > 128) {
         return func.fail("TODO: floatFromInt for integers/floats with bitsize {d} bits", .{op_info.bits});
     }
 
     if (op_info.bits > 64 or (dest_bits > 64 or dest_bits < 32)) {
         const op_bitsize = if (op_info.bits <= 16) 16 else std.math.ceilPowerOfTwoAssert(u16, op_info.bits);
 
         var fn_name_buf: [16]u8 = undefined;
         const fn_name = std.fmt.bufPrint(&fn_name_buf, "__float{s}{s}i{s}f", .{
             switch (op_info.signedness) {
                 .signed => "",
                 .unsigned => "un",
             },
             target_util.compilerRtIntAbbrev(op_bitsize),
             target_util.compilerRtFloatAbbrev(dest_bits),
         }) catch unreachable;
 
         const result = try (try func.callIntrinsic(fn_name, &.{op_ty.ip_index}, dest_ty, &.{operand})).toLocal(func, dest_ty);
         return func.finishAir(inst, result, &.{ty_op.operand});
     }
 
     try func.emitWValue(operand);
     const op = buildOpcode(.{
         .op = .convert,
         .valtype1 = typeToValtype(dest_ty, mod),
         .valtype2 = typeToValtype(op_ty, mod),
         .signedness = op_info.signedness,
     });
     try func.addTag(Mir.Inst.Tag.fromOpcode(op));
 
     const result = try func.allocLocal(dest_ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airSplat(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand = try func.resolveInst(ty_op.operand);
     const ty = func.typeOfIndex(inst);
     const elem_ty = ty.childType(mod);
 
     if (determineSimdStoreStrategy(ty, mod) == .direct) blk: {
         switch (operand) {
             // when the operand lives in the linear memory section, we can directly
             // load and splat the value at once. Meaning we do not first have to load
             // the scalar value onto the stack.
             .stack_offset, .memory, .memory_offset => {
                 const opcode = switch (elem_ty.bitSize(mod)) {
                     8 => std.wasm.simdOpcode(.v128_load8_splat),
                     16 => std.wasm.simdOpcode(.v128_load16_splat),
                     32 => std.wasm.simdOpcode(.v128_load32_splat),
                     64 => std.wasm.simdOpcode(.v128_load64_splat),
                     else => break :blk, // Cannot make use of simd-instructions
                 };
                 const result = try func.allocLocal(ty);
                 try func.emitWValue(operand);
                 // TODO: Add helper functions for simd opcodes
                 const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
                 // stores as := opcode, offset, alignment (opcode::memarg)
                 try func.mir_extra.appendSlice(func.gpa, &[_]u32{
                     opcode,
                     operand.offset(),
                     @intCast(elem_ty.abiAlignment(mod).toByteUnitsOptional().?),
                 });
                 try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
                 try func.addLabel(.local_set, result.local.value);
                 return func.finishAir(inst, result, &.{ty_op.operand});
             },
             .local => {
                 const opcode = switch (elem_ty.bitSize(mod)) {
                     8 => std.wasm.simdOpcode(.i8x16_splat),
                     16 => std.wasm.simdOpcode(.i16x8_splat),
                     32 => if (elem_ty.isInt(mod)) std.wasm.simdOpcode(.i32x4_splat) else std.wasm.simdOpcode(.f32x4_splat),
                     64 => if (elem_ty.isInt(mod)) std.wasm.simdOpcode(.i64x2_splat) else std.wasm.simdOpcode(.f64x2_splat),
                     else => break :blk, // Cannot make use of simd-instructions
                 };
                 const result = try func.allocLocal(ty);
                 try func.emitWValue(operand);
                 const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
                 try func.mir_extra.append(func.gpa, opcode);
                 try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
                 try func.addLabel(.local_set, result.local.value);
                 return func.finishAir(inst, result, &.{ty_op.operand});
             },
             else => unreachable,
         }
     }
     const elem_size = elem_ty.bitSize(mod);
     const vector_len = @as(usize, @intCast(ty.vectorLen(mod)));
     if ((!std.math.isPowerOfTwo(elem_size) or elem_size % 8 != 0) and vector_len > 1) {
         return func.fail("TODO: WebAssembly `@splat` for arbitrary element bitsize {d}", .{elem_size});
     }
 
     const result = try func.allocStack(ty);
     const elem_byte_size = @as(u32, @intCast(elem_ty.abiSize(mod)));
     var index: usize = 0;
     var offset: u32 = 0;
     while (index < vector_len) : (index += 1) {
         try func.store(result, operand, elem_ty, offset);
         offset += elem_byte_size;
     }
 
     return func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airSelect(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const operand = try func.resolveInst(pl_op.operand);
 
     _ = operand;
     return func.fail("TODO: Implement wasm airSelect", .{});
 }
 
 fn airShuffle(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const inst_ty = func.typeOfIndex(inst);
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.Shuffle, ty_pl.payload).data;
 
     const a = try func.resolveInst(extra.a);
     const b = try func.resolveInst(extra.b);
     const mask = Value.fromInterned(extra.mask);
     const mask_len = extra.mask_len;
 
     const child_ty = inst_ty.childType(mod);
     const elem_size = child_ty.abiSize(mod);
 
     // TODO: One of them could be by ref; handle in loop
     if (isByRef(func.typeOf(extra.a), mod) or isByRef(inst_ty, mod)) {
         const result = try func.allocStack(inst_ty);
 
         for (0..mask_len) |index| {
             const value = (try mask.elemValue(mod, index)).toSignedInt(mod);
 
             try func.emitWValue(result);
 
             const loaded = if (value >= 0)
                 try func.load(a, child_ty, @as(u32, @intCast(@as(i64, @intCast(elem_size)) * value)))
             else
                 try func.load(b, child_ty, @as(u32, @intCast(@as(i64, @intCast(elem_size)) * ~value)));
 
             try func.store(.stack, loaded, child_ty, result.stack_offset.value + @as(u32, @intCast(elem_size)) * @as(u32, @intCast(index)));
         }
 
         return func.finishAir(inst, result, &.{ extra.a, extra.b });
     } else {
         var operands = [_]u32{
             std.wasm.simdOpcode(.i8x16_shuffle),
         } ++ [1]u32{undefined} ** 4;
 
         var lanes = mem.asBytes(operands[1..]);
         for (0..@as(usize, @intCast(mask_len))) |index| {
             const mask_elem = (try mask.elemValue(mod, index)).toSignedInt(mod);
             const base_index = if (mask_elem >= 0)
                 @as(u8, @intCast(@as(i64, @intCast(elem_size)) * mask_elem))
             else
                 16 + @as(u8, @intCast(@as(i64, @intCast(elem_size)) * ~mask_elem));
 
             for (0..@as(usize, @intCast(elem_size))) |byte_offset| {
                 lanes[index * @as(usize, @intCast(elem_size)) + byte_offset] = base_index + @as(u8, @intCast(byte_offset));
             }
         }
 
         try func.emitWValue(a);
         try func.emitWValue(b);
 
         const extra_index = @as(u32, @intCast(func.mir_extra.items.len));
         try func.mir_extra.appendSlice(func.gpa, &operands);
         try func.addInst(.{ .tag = .simd_prefix, .data = .{ .payload = extra_index } });
 
         return func.finishAir(inst, try WValue.toLocal(.stack, func, inst_ty), &.{ extra.a, extra.b });
     }
 }
 
 fn airReduce(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const reduce = func.air.instructions.items(.data)[@intFromEnum(inst)].reduce;
     const operand = try func.resolveInst(reduce.operand);
 
     _ = operand;
     return func.fail("TODO: Implement wasm airReduce", .{});
 }
 
 fn airAggregateInit(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const result_ty = func.typeOfIndex(inst);
     const len = @as(usize, @intCast(result_ty.arrayLen(mod)));
     const elements = @as([]const Air.Inst.Ref, @ptrCast(func.air.extra[ty_pl.payload..][0..len]));
 
     const result: WValue = result_value: {
         switch (result_ty.zigTypeTag(mod)) {
             .Array => {
                 const result = try func.allocStack(result_ty);
                 const elem_ty = result_ty.childType(mod);
                 const elem_size = @as(u32, @intCast(elem_ty.abiSize(mod)));
                 const sentinel = if (result_ty.sentinel(mod)) |sent| blk: {
                     break :blk try func.lowerConstant(sent, elem_ty);
                 } else null;
 
                 // When the element type is by reference, we must copy the entire
                 // value. It is therefore safer to move the offset pointer and store
                 // each value individually, instead of using store offsets.
                 if (isByRef(elem_ty, mod)) {
                     // copy stack pointer into a temporary local, which is
                     // moved for each element to store each value in the right position.
                     const offset = try func.buildPointerOffset(result, 0, .new);
                     for (elements, 0..) |elem, elem_index| {
                         const elem_val = try func.resolveInst(elem);
                         try func.store(offset, elem_val, elem_ty, 0);
 
                         if (elem_index < elements.len - 1 and sentinel == null) {
                             _ = try func.buildPointerOffset(offset, elem_size, .modify);
                         }
                     }
                     if (sentinel) |sent| {
                         try func.store(offset, sent, elem_ty, 0);
                     }
                 } else {
                     var offset: u32 = 0;
                     for (elements) |elem| {
                         const elem_val = try func.resolveInst(elem);
                         try func.store(result, elem_val, elem_ty, offset);
                         offset += elem_size;
                     }
                     if (sentinel) |sent| {
                         try func.store(result, sent, elem_ty, offset);
                     }
                 }
                 break :result_value result;
             },
             .Struct => switch (result_ty.containerLayout(mod)) {
                 .Packed => {
                     if (isByRef(result_ty, mod)) {
                         return func.fail("TODO: airAggregateInit for packed structs larger than 64 bits", .{});
                     }
                     const packed_struct = mod.typeToPackedStruct(result_ty).?;
                     const field_types = packed_struct.field_types;
                     const backing_type = Type.fromInterned(packed_struct.backingIntType(ip).*);
 
                     // ensure the result is zero'd
                     const result = try func.allocLocal(backing_type);
                     if (backing_type.bitSize(mod) <= 32)
                         try func.addImm32(0)
                     else
                         try func.addImm64(0);
                     try func.addLabel(.local_set, result.local.value);
 
                     var current_bit: u16 = 0;
                     for (elements, 0..) |elem, elem_index| {
                         const field_ty = Type.fromInterned(field_types.get(ip)[elem_index]);
                         if (!field_ty.hasRuntimeBitsIgnoreComptime(mod)) continue;
 
                         const shift_val = if (backing_type.bitSize(mod) <= 32)
                             WValue{ .imm32 = current_bit }
                         else
                             WValue{ .imm64 = current_bit };
 
                         const value = try func.resolveInst(elem);
                         const value_bit_size: u16 = @intCast(field_ty.bitSize(mod));
                         const int_ty = try mod.intType(.unsigned, value_bit_size);
 
                         // load our current result on stack so we can perform all transformations
                         // using only stack values. Saving the cost of loads and stores.
                         try func.emitWValue(result);
                         const bitcasted = try func.bitcast(int_ty, field_ty, value);
                         const extended_val = try func.intcast(bitcasted, int_ty, backing_type);
                         // no need to shift any values when the current offset is 0
                         const shifted = if (current_bit != 0) shifted: {
                             break :shifted try func.binOp(extended_val, shift_val, backing_type, .shl);
                         } else extended_val;
                         // we ignore the result as we keep it on the stack to assign it directly to `result`
                         _ = try func.binOp(.stack, shifted, backing_type, .@"or");
                         try func.addLabel(.local_set, result.local.value);
                         current_bit += value_bit_size;
                     }
                     break :result_value result;
                 },
                 else => {
                     const result = try func.allocStack(result_ty);
                     const offset = try func.buildPointerOffset(result, 0, .new); // pointer to offset
                     var prev_field_offset: u64 = 0;
                     for (elements, 0..) |elem, elem_index| {
                         if ((try result_ty.structFieldValueComptime(mod, elem_index)) != null) continue;
 
                         const elem_ty = result_ty.structFieldType(elem_index, mod);
                         const field_offset = result_ty.structFieldOffset(elem_index, mod);
                         _ = try func.buildPointerOffset(offset, @intCast(field_offset - prev_field_offset), .modify);
                         prev_field_offset = field_offset;
 
                         const value = try func.resolveInst(elem);
                         try func.store(offset, value, elem_ty, 0);
                     }
 
                     break :result_value result;
                 },
             },
             .Vector => return func.fail("TODO: Wasm backend: implement airAggregateInit for vectors", .{}),
             else => unreachable,
         }
     };
 
     if (elements.len <= Liveness.bpi - 1) {
         var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
         @memcpy(buf[0..elements.len], elements);
         return func.finishAir(inst, result, &buf);
     }
     var bt = try func.iterateBigTomb(inst, elements.len);
     for (elements) |arg| bt.feed(arg);
     return bt.finishAir(result);
 }
 
 fn airUnionInit(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ip = &mod.intern_pool;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.UnionInit, ty_pl.payload).data;
 
     const result = result: {
         const union_ty = func.typeOfIndex(inst);
         const layout = union_ty.unionGetLayout(mod);
         const union_obj = mod.typeToUnion(union_ty).?;
         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[extra.field_index]);
         const field_name = union_obj.field_names.get(ip)[extra.field_index];
 
         const tag_int = blk: {
             const tag_ty = union_ty.unionTagTypeHypothetical(mod);
             const enum_field_index = tag_ty.enumFieldIndex(field_name, mod).?;
             const tag_val = try mod.enumValueFieldIndex(tag_ty, enum_field_index);
             break :blk try func.lowerConstant(tag_val, tag_ty);
         };
         if (layout.payload_size == 0) {
             if (layout.tag_size == 0) {
                 break :result WValue{ .none = {} };
             }
             assert(!isByRef(union_ty, mod));
             break :result tag_int;
         }
 
         if (isByRef(union_ty, mod)) {
             const result_ptr = try func.allocStack(union_ty);
             const payload = try func.resolveInst(extra.init);
             if (layout.tag_align.compare(.gte, layout.payload_align)) {
                 if (isByRef(field_ty, mod)) {
                     const payload_ptr = try func.buildPointerOffset(result_ptr, layout.tag_size, .new);
                     try func.store(payload_ptr, payload, field_ty, 0);
                 } else {
                     try func.store(result_ptr, payload, field_ty, @intCast(layout.tag_size));
                 }
 
                 if (layout.tag_size > 0) {
                     try func.store(result_ptr, tag_int, Type.fromInterned(union_obj.enum_tag_ty), 0);
                 }
             } else {
                 try func.store(result_ptr, payload, field_ty, 0);
                 if (layout.tag_size > 0) {
                     try func.store(
                         result_ptr,
                         tag_int,
                         Type.fromInterned(union_obj.enum_tag_ty),
                         @intCast(layout.payload_size),
                     );
                 }
             }
             break :result result_ptr;
         } else {
             const operand = try func.resolveInst(extra.init);
             const union_int_type = try mod.intType(.unsigned, @as(u16, @intCast(union_ty.bitSize(mod))));
             if (field_ty.zigTypeTag(mod) == .Float) {
                 const int_type = try mod.intType(.unsigned, @intCast(field_ty.bitSize(mod)));
                 const bitcasted = try func.bitcast(field_ty, int_type, operand);
                 const casted = try func.trunc(bitcasted, int_type, union_int_type);
                 break :result try casted.toLocal(func, field_ty);
             } else if (field_ty.isPtrAtRuntime(mod)) {
                 const int_type = try mod.intType(.unsigned, @intCast(field_ty.bitSize(mod)));
                 const casted = try func.intcast(operand, int_type, union_int_type);
                 break :result try casted.toLocal(func, field_ty);
             }
             const casted = try func.intcast(operand, field_ty, union_int_type);
             break :result try casted.toLocal(func, field_ty);
         }
     };
 
     return func.finishAir(inst, result, &.{extra.init});
 }
 
 fn airPrefetch(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const prefetch = func.air.instructions.items(.data)[@intFromEnum(inst)].prefetch;
     func.finishAir(inst, .none, &.{prefetch.ptr});
 }
 
 fn airWasmMemorySize(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
 
     const result = try func.allocLocal(func.typeOfIndex(inst));
     try func.addLabel(.memory_size, pl_op.payload);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{pl_op.operand});
 }
 
 fn airWasmMemoryGrow(func: *CodeGen, inst: Air.Inst.Index) !void {
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
 
     const operand = try func.resolveInst(pl_op.operand);
     const result = try func.allocLocal(func.typeOfIndex(inst));
     try func.emitWValue(operand);
     try func.addLabel(.memory_grow, pl_op.payload);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{pl_op.operand});
 }
 
 fn cmpOptionals(func: *CodeGen, lhs: WValue, rhs: WValue, operand_ty: Type, op: std.math.CompareOperator) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(operand_ty.hasRuntimeBitsIgnoreComptime(mod));
     assert(op == .eq or op == .neq);
     const payload_ty = operand_ty.optionalChild(mod);
 
     // We store the final result in here that will be validated
     // if the optional is truly equal.
     var result = try func.ensureAllocLocal(Type.i32);
     defer result.free(func);
 
     try func.startBlock(.block, wasm.block_empty);
     _ = try func.isNull(lhs, operand_ty, .i32_eq);
     _ = try func.isNull(rhs, operand_ty, .i32_eq);
     try func.addTag(.i32_ne); // inverse so we can exit early
     try func.addLabel(.br_if, 0);
 
     _ = try func.load(lhs, payload_ty, 0);
     _ = try func.load(rhs, payload_ty, 0);
     const opcode = buildOpcode(.{ .op = .ne, .valtype1 = typeToValtype(payload_ty, mod) });
     try func.addTag(Mir.Inst.Tag.fromOpcode(opcode));
     try func.addLabel(.br_if, 0);
 
     try func.addImm32(1);
     try func.addLabel(.local_set, result.local.value);
     try func.endBlock();
 
     try func.emitWValue(result);
     try func.addImm32(0);
     try func.addTag(if (op == .eq) .i32_ne else .i32_eq);
     return WValue{ .stack = {} };
 }
 
 /// Compares big integers by checking both its high bits and low bits.
 /// NOTE: Leaves the result of the comparison on top of the stack.
 /// TODO: Lower this to compiler_rt call when bitsize > 128
 fn cmpBigInt(func: *CodeGen, lhs: WValue, rhs: WValue, operand_ty: Type, op: std.math.CompareOperator) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(operand_ty.abiSize(mod) >= 16);
     assert(!(lhs != .stack and rhs == .stack));
     if (operand_ty.bitSize(mod) > 128) {
         return func.fail("TODO: Support cmpBigInt for integer bitsize: '{d}'", .{operand_ty.bitSize(mod)});
     }
 
     var lhs_high_bit = try (try func.load(lhs, Type.u64, 0)).toLocal(func, Type.u64);
     defer lhs_high_bit.free(func);
     var rhs_high_bit = try (try func.load(rhs, Type.u64, 0)).toLocal(func, Type.u64);
     defer rhs_high_bit.free(func);
 
     switch (op) {
         .eq, .neq => {
             const xor_high = try func.binOp(lhs_high_bit, rhs_high_bit, Type.u64, .xor);
             const lhs_low_bit = try func.load(lhs, Type.u64, 8);
             const rhs_low_bit = try func.load(rhs, Type.u64, 8);
             const xor_low = try func.binOp(lhs_low_bit, rhs_low_bit, Type.u64, .xor);
             const or_result = try func.binOp(xor_high, xor_low, Type.u64, .@"or");
 
             switch (op) {
                 .eq => return func.cmp(or_result, .{ .imm64 = 0 }, Type.u64, .eq),
                 .neq => return func.cmp(or_result, .{ .imm64 = 0 }, Type.u64, .neq),
                 else => unreachable,
             }
         },
         else => {
             const ty = if (operand_ty.isSignedInt(mod)) Type.i64 else Type.u64;
             // leave those value on top of the stack for '.select'
             const lhs_low_bit = try func.load(lhs, Type.u64, 8);
             const rhs_low_bit = try func.load(rhs, Type.u64, 8);
             _ = try func.cmp(lhs_low_bit, rhs_low_bit, ty, op);
             _ = try func.cmp(lhs_high_bit, rhs_high_bit, ty, op);
             _ = try func.cmp(lhs_high_bit, rhs_high_bit, ty, .eq);
             try func.addTag(.select);
         },
     }
 
     return WValue{ .stack = {} };
 }
 
 fn airSetUnionTag(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
     const un_ty = func.typeOf(bin_op.lhs).childType(mod);
     const tag_ty = func.typeOf(bin_op.rhs);
     const layout = un_ty.unionGetLayout(mod);
     if (layout.tag_size == 0) return func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 
     const union_ptr = try func.resolveInst(bin_op.lhs);
     const new_tag = try func.resolveInst(bin_op.rhs);
     if (layout.payload_size == 0) {
         try func.store(union_ptr, new_tag, tag_ty, 0);
         return func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
     }
 
     // when the tag alignment is smaller than the payload, the field will be stored
     // after the payload.
     const offset: u32 = if (layout.tag_align.compare(.lt, layout.payload_align)) blk: {
         break :blk @intCast(layout.payload_size);
     } else 0;
     try func.store(union_ptr, new_tag, tag_ty, offset);
     func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airGetUnionTag(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const un_ty = func.typeOf(ty_op.operand);
     const tag_ty = func.typeOfIndex(inst);
     const layout = un_ty.unionGetLayout(mod);
     if (layout.tag_size == 0) return func.finishAir(inst, .none, &.{ty_op.operand});
 
     const operand = try func.resolveInst(ty_op.operand);
     // when the tag alignment is smaller than the payload, the field will be stored
     // after the payload.
     const offset: u32 = if (layout.tag_align.compare(.lt, layout.payload_align)) blk: {
         break :blk @intCast(layout.payload_size);
     } else 0;
     const tag = try func.load(operand, tag_ty, offset);
     const result = try tag.toLocal(func, tag_ty);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airFpext(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const dest_ty = func.typeOfIndex(inst);
     const operand = try func.resolveInst(ty_op.operand);
     const extended = try func.fpext(operand, func.typeOf(ty_op.operand), dest_ty);
     const result = try extended.toLocal(func, dest_ty);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 /// Extends a float from a given `Type` to a larger wanted `Type`
 /// NOTE: Leaves the result on the stack
 fn fpext(func: *CodeGen, operand: WValue, given: Type, wanted: Type) InnerError!WValue {
     const given_bits = given.floatBits(func.target);
     const wanted_bits = wanted.floatBits(func.target);
 
     if (wanted_bits == 64 and given_bits == 32) {
         try func.emitWValue(operand);
         try func.addTag(.f64_promote_f32);
         return WValue{ .stack = {} };
     } else if (given_bits == 16 and wanted_bits <= 64) {
         // call __extendhfsf2(f16) f32
         const f32_result = try func.callIntrinsic(
             "__extendhfsf2",
             &.{.f16_type},
             Type.f32,
             &.{operand},
         );
         std.debug.assert(f32_result == .stack);
 
         if (wanted_bits == 64) {
             try func.addTag(.f64_promote_f32);
         }
         return WValue{ .stack = {} };
     }
 
     var fn_name_buf: [13]u8 = undefined;
     const fn_name = std.fmt.bufPrint(&fn_name_buf, "__extend{s}f{s}f2", .{
         target_util.compilerRtFloatAbbrev(given_bits),
         target_util.compilerRtFloatAbbrev(wanted_bits),
     }) catch unreachable;
 
     return func.callIntrinsic(fn_name, &.{given.ip_index}, wanted, &.{operand});
 }
 
 fn airFptrunc(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const dest_ty = func.typeOfIndex(inst);
     const operand = try func.resolveInst(ty_op.operand);
     const truncated = try func.fptrunc(operand, func.typeOf(ty_op.operand), dest_ty);
     const result = try truncated.toLocal(func, dest_ty);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 /// Truncates a float from a given `Type` to its wanted `Type`
 /// NOTE: The result value remains on the stack
 fn fptrunc(func: *CodeGen, operand: WValue, given: Type, wanted: Type) InnerError!WValue {
     const given_bits = given.floatBits(func.target);
     const wanted_bits = wanted.floatBits(func.target);
 
     if (wanted_bits == 32 and given_bits == 64) {
         try func.emitWValue(operand);
         try func.addTag(.f32_demote_f64);
         return WValue{ .stack = {} };
     } else if (wanted_bits == 16 and given_bits <= 64) {
         const op: WValue = if (given_bits == 64) blk: {
             try func.emitWValue(operand);
             try func.addTag(.f32_demote_f64);
             break :blk WValue{ .stack = {} };
         } else operand;
 
         // call __truncsfhf2(f32) f16
         return func.callIntrinsic("__truncsfhf2", &.{.f32_type}, Type.f16, &.{op});
     }
 
     var fn_name_buf: [12]u8 = undefined;
     const fn_name = std.fmt.bufPrint(&fn_name_buf, "__trunc{s}f{s}f2", .{
         target_util.compilerRtFloatAbbrev(given_bits),
         target_util.compilerRtFloatAbbrev(wanted_bits),
     }) catch unreachable;
 
     return func.callIntrinsic(fn_name, &.{given.ip_index}, wanted, &.{operand});
 }
 
 fn airErrUnionPayloadPtrSet(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const err_set_ty = func.typeOf(ty_op.operand).childType(mod);
     const payload_ty = err_set_ty.errorUnionPayload(mod);
     const operand = try func.resolveInst(ty_op.operand);
 
     // set error-tag to '0' to annotate error union is non-error
     try func.store(
         operand,
         .{ .imm32 = 0 },
         Type.anyerror,
         @as(u32, @intCast(errUnionErrorOffset(payload_ty, mod))),
     );
 
     const result = result: {
         if (!payload_ty.hasRuntimeBitsIgnoreComptime(mod)) {
             break :result func.reuseOperand(ty_op.operand, operand);
         }
 
         break :result try func.buildPointerOffset(operand, @as(u32, @intCast(errUnionPayloadOffset(payload_ty, mod))), .new);
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airFieldParentPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.FieldParentPtr, ty_pl.payload).data;
 
     const field_ptr = try func.resolveInst(extra.field_ptr);
     const parent_ty = ty_pl.ty.toType().childType(mod);
     const field_offset = parent_ty.structFieldOffset(extra.field_index, mod);
 
     const result = if (field_offset != 0) result: {
         const base = try func.buildPointerOffset(field_ptr, 0, .new);
         try func.addLabel(.local_get, base.local.value);
         try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(field_offset)))));
         try func.addTag(.i32_sub);
         try func.addLabel(.local_set, base.local.value);
         break :result base;
     } else func.reuseOperand(extra.field_ptr, field_ptr);
 
     func.finishAir(inst, result, &.{extra.field_ptr});
 }
 
 fn sliceOrArrayPtr(func: *CodeGen, ptr: WValue, ptr_ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     if (ptr_ty.isSlice(mod)) {
         return func.slicePtr(ptr);
     } else {
         return ptr;
     }
 }
 
 fn airMemcpy(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
     const dst = try func.resolveInst(bin_op.lhs);
     const dst_ty = func.typeOf(bin_op.lhs);
     const ptr_elem_ty = dst_ty.childType(mod);
     const src = try func.resolveInst(bin_op.rhs);
     const src_ty = func.typeOf(bin_op.rhs);
     const len = switch (dst_ty.ptrSize(mod)) {
         .Slice => blk: {
             const slice_len = try func.sliceLen(dst);
             if (ptr_elem_ty.abiSize(mod) != 1) {
                 try func.emitWValue(slice_len);
                 try func.emitWValue(.{ .imm32 = @as(u32, @intCast(ptr_elem_ty.abiSize(mod))) });
                 try func.addTag(.i32_mul);
                 try func.addLabel(.local_set, slice_len.local.value);
             }
             break :blk slice_len;
         },
         .One => @as(WValue, .{
             .imm32 = @as(u32, @intCast(ptr_elem_ty.arrayLen(mod) * ptr_elem_ty.childType(mod).abiSize(mod))),
         }),
         .C, .Many => unreachable,
     };
     const dst_ptr = try func.sliceOrArrayPtr(dst, dst_ty);
     const src_ptr = try func.sliceOrArrayPtr(src, src_ty);
     try func.memcpy(dst_ptr, src_ptr, len);
 
     func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airRetAddr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     // TODO: Implement this properly once stack serialization is solved
     func.finishAir(inst, switch (func.arch()) {
         .wasm32 => .{ .imm32 = 0 },
         .wasm64 => .{ .imm64 = 0 },
         else => unreachable,
     }, &.{});
 }
 
 fn airPopcount(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const op_ty = func.typeOf(ty_op.operand);
     const result_ty = func.typeOfIndex(inst);
 
     if (op_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement @popCount for vectors", .{});
     }
 
     const int_info = op_ty.intInfo(mod);
     const bits = int_info.bits;
     const wasm_bits = toWasmBits(bits) orelse {
         return func.fail("TODO: Implement @popCount for integers with bitsize '{d}'", .{bits});
     };
 
     switch (wasm_bits) {
         128 => {
             _ = try func.load(operand, Type.u64, 0);
             try func.addTag(.i64_popcnt);
             _ = try func.load(operand, Type.u64, 8);
             try func.addTag(.i64_popcnt);
             try func.addTag(.i64_add);
             try func.addTag(.i32_wrap_i64);
         },
         else => {
             try func.emitWValue(operand);
             switch (wasm_bits) {
                 32 => try func.addTag(.i32_popcnt),
                 64 => {
                     try func.addTag(.i64_popcnt);
                     try func.addTag(.i32_wrap_i64);
                 },
                 else => unreachable,
             }
         },
     }
 
     const result = try func.allocLocal(result_ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airErrorName(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
 
     const operand = try func.resolveInst(un_op);
     // First retrieve the symbol index to the error name table
     // that will be used to emit a relocation for the pointer
     // to the error name table.
     //
     // Each entry to this table is a slice (ptr+len).
     // The operand in this instruction represents the index within this table.
     // This means to get the final name, we emit the base pointer and then perform
     // pointer arithmetic to find the pointer to this slice and return that.
     //
     // As the names are global and the slice elements are constant, we do not have
     // to make a copy of the ptr+value but can point towards them directly.
     const error_table_symbol = try func.bin_file.getErrorTableSymbol();
     const name_ty = Type.slice_const_u8_sentinel_0;
     const mod = func.bin_file.base.comp.module.?;
     const abi_size = name_ty.abiSize(mod);
 
     const error_name_value: WValue = .{ .memory = error_table_symbol }; // emitting this will create a relocation
     try func.emitWValue(error_name_value);
     try func.emitWValue(operand);
     switch (func.arch()) {
         .wasm32 => {
             try func.addImm32(@as(i32, @bitCast(@as(u32, @intCast(abi_size)))));
             try func.addTag(.i32_mul);
             try func.addTag(.i32_add);
         },
         .wasm64 => {
             try func.addImm64(abi_size);
             try func.addTag(.i64_mul);
             try func.addTag(.i64_add);
         },
         else => unreachable,
     }
 
     const result_ptr = try func.allocLocal(Type.usize);
     try func.addLabel(.local_set, result_ptr.local.value);
     func.finishAir(inst, result_ptr, &.{un_op});
 }
 
 fn airPtrSliceFieldPtr(func: *CodeGen, inst: Air.Inst.Index, offset: u32) InnerError!void {
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const slice_ptr = try func.resolveInst(ty_op.operand);
     const result = try func.buildPointerOffset(slice_ptr, offset, .new);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airAddSubWithOverflow(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     assert(op == .add or op == .sub);
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const lhs_op = try func.resolveInst(extra.lhs);
     const rhs_op = try func.resolveInst(extra.rhs);
     const lhs_ty = func.typeOf(extra.lhs);
     const mod = func.bin_file.base.comp.module.?;
 
     if (lhs_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement overflow arithmetic for vectors", .{});
     }
 
     const int_info = lhs_ty.intInfo(mod);
     const is_signed = int_info.signedness == .signed;
     const wasm_bits = toWasmBits(int_info.bits) orelse {
         return func.fail("TODO: Implement {{add/sub}}_with_overflow for integer bitsize: {d}", .{int_info.bits});
     };
 
     if (wasm_bits == 128) {
         const result = try func.addSubWithOverflowBigInt(lhs_op, rhs_op, lhs_ty, func.typeOfIndex(inst), op);
         return func.finishAir(inst, result, &.{ extra.lhs, extra.rhs });
     }
 
     const zero = switch (wasm_bits) {
         32 => WValue{ .imm32 = 0 },
         64 => WValue{ .imm64 = 0 },
         else => unreachable,
     };
 
     // for signed integers, we first apply signed shifts by the difference in bits
     // to get the signed value, as we store it internally as 2's complement.
     var lhs = if (wasm_bits != int_info.bits and is_signed) blk: {
         break :blk try (try func.signExtendInt(lhs_op, lhs_ty)).toLocal(func, lhs_ty);
     } else lhs_op;
     var rhs = if (wasm_bits != int_info.bits and is_signed) blk: {
         break :blk try (try func.signExtendInt(rhs_op, lhs_ty)).toLocal(func, lhs_ty);
     } else rhs_op;
 
     // in this case, we performed a signExtendInt which created a temporary local
     // so let's free this so it can be re-used instead.
     // In the other case we do not want to free it, because that would free the
     // resolved instructions which may be referenced by other instructions.
     defer if (wasm_bits != int_info.bits and is_signed) {
         lhs.free(func);
         rhs.free(func);
     };
 
     const bin_op = try (try func.binOp(lhs, rhs, lhs_ty, op)).toLocal(func, lhs_ty);
     var result = if (wasm_bits != int_info.bits) blk: {
         break :blk try (try func.wrapOperand(bin_op, lhs_ty)).toLocal(func, lhs_ty);
     } else bin_op;
     defer result.free(func);
 
     const cmp_op: std.math.CompareOperator = if (op == .sub) .gt else .lt;
     const overflow_bit: WValue = if (is_signed) blk: {
         if (wasm_bits == int_info.bits) {
             const cmp_zero = try func.cmp(rhs, zero, lhs_ty, cmp_op);
             const lt = try func.cmp(bin_op, lhs, lhs_ty, .lt);
             break :blk try func.binOp(cmp_zero, lt, Type.u32, .xor);
         }
         const abs = try func.signExtendInt(bin_op, lhs_ty);
         break :blk try func.cmp(abs, bin_op, lhs_ty, .neq);
     } else if (wasm_bits == int_info.bits)
         try func.cmp(bin_op, lhs, lhs_ty, cmp_op)
     else
         try func.cmp(bin_op, result, lhs_ty, .neq);
     var overflow_local = try overflow_bit.toLocal(func, Type.u32);
     defer overflow_local.free(func);
 
     const result_ptr = try func.allocStack(func.typeOfIndex(inst));
     try func.store(result_ptr, result, lhs_ty, 0);
     const offset = @as(u32, @intCast(lhs_ty.abiSize(mod)));
     try func.store(result_ptr, overflow_local, Type.u1, offset);
 
     func.finishAir(inst, result_ptr, &.{ extra.lhs, extra.rhs });
 }
 
 fn addSubWithOverflowBigInt(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type, result_ty: Type, op: Op) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     assert(op == .add or op == .sub);
     const int_info = ty.intInfo(mod);
     const is_signed = int_info.signedness == .signed;
     if (int_info.bits != 128) {
         return func.fail("TODO: Implement @{{add/sub}}WithOverflow for integer bitsize '{d}'", .{int_info.bits});
     }
 
     var lhs_high_bit = try (try func.load(lhs, Type.u64, 0)).toLocal(func, Type.u64);
     defer lhs_high_bit.free(func);
     var lhs_low_bit = try (try func.load(lhs, Type.u64, 8)).toLocal(func, Type.u64);
     defer lhs_low_bit.free(func);
     var rhs_high_bit = try (try func.load(rhs, Type.u64, 0)).toLocal(func, Type.u64);
     defer rhs_high_bit.free(func);
     var rhs_low_bit = try (try func.load(rhs, Type.u64, 8)).toLocal(func, Type.u64);
     defer rhs_low_bit.free(func);
 
     var low_op_res = try (try func.binOp(lhs_low_bit, rhs_low_bit, Type.u64, op)).toLocal(func, Type.u64);
     defer low_op_res.free(func);
     var high_op_res = try (try func.binOp(lhs_high_bit, rhs_high_bit, Type.u64, op)).toLocal(func, Type.u64);
     defer high_op_res.free(func);
 
     var lt = if (op == .add) blk: {
         break :blk try (try func.cmp(high_op_res, lhs_high_bit, Type.u64, .lt)).toLocal(func, Type.u32);
     } else if (op == .sub) blk: {
         break :blk try (try func.cmp(lhs_high_bit, rhs_high_bit, Type.u64, .lt)).toLocal(func, Type.u32);
     } else unreachable;
     defer lt.free(func);
     var tmp = try (try func.intcast(lt, Type.u32, Type.u64)).toLocal(func, Type.u64);
     defer tmp.free(func);
     var tmp_op = try (try func.binOp(low_op_res, tmp, Type.u64, op)).toLocal(func, Type.u64);
     defer tmp_op.free(func);
 
     const overflow_bit = if (is_signed) blk: {
         const xor_low = try func.binOp(lhs_low_bit, rhs_low_bit, Type.u64, .xor);
         const to_wrap = if (op == .add) wrap: {
             break :wrap try func.binOp(xor_low, .{ .imm64 = ~@as(u64, 0) }, Type.u64, .xor);
         } else xor_low;
         const xor_op = try func.binOp(lhs_low_bit, tmp_op, Type.u64, .xor);
         const wrap = try func.binOp(to_wrap, xor_op, Type.u64, .@"and");
         break :blk try func.cmp(wrap, .{ .imm64 = 0 }, Type.i64, .lt); // i64 because signed
     } else blk: {
         const first_arg = if (op == .sub) arg: {
             break :arg try func.cmp(high_op_res, lhs_high_bit, Type.u64, .gt);
         } else lt;
 
         try func.emitWValue(first_arg);
         _ = try func.cmp(tmp_op, lhs_low_bit, Type.u64, if (op == .add) .lt else .gt);
         _ = try func.cmp(tmp_op, lhs_low_bit, Type.u64, .eq);
         try func.addTag(.select);
 
         break :blk WValue{ .stack = {} };
     };
     var overflow_local = try overflow_bit.toLocal(func, Type.u1);
     defer overflow_local.free(func);
 
     const result_ptr = try func.allocStack(result_ty);
     try func.store(result_ptr, high_op_res, Type.u64, 0);
     try func.store(result_ptr, tmp_op, Type.u64, 8);
     try func.store(result_ptr, overflow_local, Type.u1, 16);
 
     return result_ptr;
 }
 
 fn airShlWithOverflow(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const lhs = try func.resolveInst(extra.lhs);
     const rhs = try func.resolveInst(extra.rhs);
     const lhs_ty = func.typeOf(extra.lhs);
     const rhs_ty = func.typeOf(extra.rhs);
 
     if (lhs_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement overflow arithmetic for vectors", .{});
     }
 
     const int_info = lhs_ty.intInfo(mod);
     const is_signed = int_info.signedness == .signed;
     const wasm_bits = toWasmBits(int_info.bits) orelse {
         return func.fail("TODO: Implement shl_with_overflow for integer bitsize: {d}", .{int_info.bits});
     };
 
     // Ensure rhs is coerced to lhs as they must have the same WebAssembly types
     // before we can perform any binary operation.
     const rhs_wasm_bits = toWasmBits(rhs_ty.intInfo(mod).bits).?;
     const rhs_final = if (wasm_bits != rhs_wasm_bits) blk: {
         const rhs_casted = try func.intcast(rhs, rhs_ty, lhs_ty);
         break :blk try rhs_casted.toLocal(func, lhs_ty);
     } else rhs;
 
     var shl = try (try func.binOp(lhs, rhs_final, lhs_ty, .shl)).toLocal(func, lhs_ty);
     defer shl.free(func);
     var result = if (wasm_bits != int_info.bits) blk: {
         break :blk try (try func.wrapOperand(shl, lhs_ty)).toLocal(func, lhs_ty);
     } else shl;
     defer result.free(func); // it's a no-op to free the same local twice (when wasm_bits == int_info.bits)
 
     const overflow_bit = if (wasm_bits != int_info.bits and is_signed) blk: {
         // emit lhs to stack to we can keep 'wrapped' on the stack also
         try func.emitWValue(lhs);
         const abs = try func.signExtendInt(shl, lhs_ty);
         const wrapped = try func.wrapBinOp(abs, rhs_final, lhs_ty, .shr);
         break :blk try func.cmp(.{ .stack = {} }, wrapped, lhs_ty, .neq);
     } else blk: {
         try func.emitWValue(lhs);
         const shr = try func.binOp(result, rhs_final, lhs_ty, .shr);
         break :blk try func.cmp(.{ .stack = {} }, shr, lhs_ty, .neq);
     };
     var overflow_local = try overflow_bit.toLocal(func, Type.u1);
     defer overflow_local.free(func);
 
     const result_ptr = try func.allocStack(func.typeOfIndex(inst));
     try func.store(result_ptr, result, lhs_ty, 0);
     const offset = @as(u32, @intCast(lhs_ty.abiSize(mod)));
     try func.store(result_ptr, overflow_local, Type.u1, offset);
 
     func.finishAir(inst, result_ptr, &.{ extra.lhs, extra.rhs });
 }
 
 fn airMulWithOverflow(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.Bin, ty_pl.payload).data;
 
     const lhs = try func.resolveInst(extra.lhs);
     const rhs = try func.resolveInst(extra.rhs);
     const lhs_ty = func.typeOf(extra.lhs);
     const mod = func.bin_file.base.comp.module.?;
 
     if (lhs_ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: Implement overflow arithmetic for vectors", .{});
     }
 
     // We store the bit if it's overflowed or not in this. As it's zero-initialized
     // we only need to update it if an overflow (or underflow) occurred.
     var overflow_bit = try func.ensureAllocLocal(Type.u1);
     defer overflow_bit.free(func);
 
     const int_info = lhs_ty.intInfo(mod);
     const wasm_bits = toWasmBits(int_info.bits) orelse {
         return func.fail("TODO: Implement `@mulWithOverflow` for integer bitsize: {d}", .{int_info.bits});
     };
 
     const zero = switch (wasm_bits) {
         32 => WValue{ .imm32 = 0 },
         64, 128 => WValue{ .imm64 = 0 },
         else => unreachable,
     };
 
     // for 32 bit integers we upcast it to a 64bit integer
     const bin_op = if (int_info.bits == 32) blk: {
         const new_ty = if (int_info.signedness == .signed) Type.i64 else Type.u64;
         const lhs_upcast = try func.intcast(lhs, lhs_ty, new_ty);
         const rhs_upcast = try func.intcast(rhs, lhs_ty, new_ty);
         const bin_op = try (try func.binOp(lhs_upcast, rhs_upcast, new_ty, .mul)).toLocal(func, new_ty);
         if (int_info.signedness == .unsigned) {
             const shr = try func.binOp(bin_op, .{ .imm64 = int_info.bits }, new_ty, .shr);
             const wrap = try func.intcast(shr, new_ty, lhs_ty);
             _ = try func.cmp(wrap, zero, lhs_ty, .neq);
             try func.addLabel(.local_set, overflow_bit.local.value);
             break :blk try func.intcast(bin_op, new_ty, lhs_ty);
         } else {
             const down_cast = try (try func.intcast(bin_op, new_ty, lhs_ty)).toLocal(func, lhs_ty);
             var shr = try (try func.binOp(down_cast, .{ .imm32 = int_info.bits - 1 }, lhs_ty, .shr)).toLocal(func, lhs_ty);
             defer shr.free(func);
 
             const shr_res = try func.binOp(bin_op, .{ .imm64 = int_info.bits }, new_ty, .shr);
             const down_shr_res = try func.intcast(shr_res, new_ty, lhs_ty);
             _ = try func.cmp(down_shr_res, shr, lhs_ty, .neq);
             try func.addLabel(.local_set, overflow_bit.local.value);
             break :blk down_cast;
         }
     } else if (int_info.signedness == .signed and wasm_bits == 32) blk: {
         const lhs_abs = try func.signExtendInt(lhs, lhs_ty);
         const rhs_abs = try func.signExtendInt(rhs, lhs_ty);
         const bin_op = try (try func.binOp(lhs_abs, rhs_abs, lhs_ty, .mul)).toLocal(func, lhs_ty);
         const mul_abs = try func.signExtendInt(bin_op, lhs_ty);
         _ = try func.cmp(mul_abs, bin_op, lhs_ty, .neq);
         try func.addLabel(.local_set, overflow_bit.local.value);
         break :blk try func.wrapOperand(bin_op, lhs_ty);
     } else if (wasm_bits == 32) blk: {
         var bin_op = try (try func.binOp(lhs, rhs, lhs_ty, .mul)).toLocal(func, lhs_ty);
         defer bin_op.free(func);
         const shift_imm = if (wasm_bits == 32)
             WValue{ .imm32 = int_info.bits }
         else
             WValue{ .imm64 = int_info.bits };
         const shr = try func.binOp(bin_op, shift_imm, lhs_ty, .shr);
         _ = try func.cmp(shr, zero, lhs_ty, .neq);
         try func.addLabel(.local_set, overflow_bit.local.value);
         break :blk try func.wrapOperand(bin_op, lhs_ty);
     } else if (int_info.bits == 64 and int_info.signedness == .unsigned) blk: {
         const new_ty = Type.u128;
         var lhs_upcast = try (try func.intcast(lhs, lhs_ty, new_ty)).toLocal(func, lhs_ty);
         defer lhs_upcast.free(func);
         var rhs_upcast = try (try func.intcast(rhs, lhs_ty, new_ty)).toLocal(func, lhs_ty);
         defer rhs_upcast.free(func);
         const bin_op = try func.binOp(lhs_upcast, rhs_upcast, new_ty, .mul);
         const lsb = try func.load(bin_op, lhs_ty, 8);
         _ = try func.cmp(lsb, zero, lhs_ty, .neq);
         try func.addLabel(.local_set, overflow_bit.local.value);
 
         break :blk try func.load(bin_op, lhs_ty, 0);
     } else if (int_info.bits == 64 and int_info.signedness == .signed) blk: {
         const shift_val: WValue = .{ .imm64 = 63 };
         var lhs_shifted = try (try func.binOp(lhs, shift_val, lhs_ty, .shr)).toLocal(func, lhs_ty);
         defer lhs_shifted.free(func);
         var rhs_shifted = try (try func.binOp(rhs, shift_val, lhs_ty, .shr)).toLocal(func, lhs_ty);
         defer rhs_shifted.free(func);
 
         const bin_op = try func.callIntrinsic(
             "__multi3",
             &[_]InternPool.Index{.i64_type} ** 4,
             Type.i128,
             &.{ lhs, lhs_shifted, rhs, rhs_shifted },
         );
         const res = try func.allocLocal(lhs_ty);
         const msb = try func.load(bin_op, lhs_ty, 0);
         try func.addLabel(.local_tee, res.local.value);
         const msb_shifted = try func.binOp(msb, shift_val, lhs_ty, .shr);
         const lsb = try func.load(bin_op, lhs_ty, 8);
         _ = try func.cmp(lsb, msb_shifted, lhs_ty, .neq);
         try func.addLabel(.local_set, overflow_bit.local.value);
         break :blk res;
     } else if (int_info.bits == 128 and int_info.signedness == .unsigned) blk: {
         var lhs_msb = try (try func.load(lhs, Type.u64, 0)).toLocal(func, Type.u64);
         defer lhs_msb.free(func);
         var lhs_lsb = try (try func.load(lhs, Type.u64, 8)).toLocal(func, Type.u64);
         defer lhs_lsb.free(func);
         var rhs_msb = try (try func.load(rhs, Type.u64, 0)).toLocal(func, Type.u64);
         defer rhs_msb.free(func);
         var rhs_lsb = try (try func.load(rhs, Type.u64, 8)).toLocal(func, Type.u64);
         defer rhs_lsb.free(func);
 
         const mul1 = try func.callIntrinsic(
             "__multi3",
             &[_]InternPool.Index{.i64_type} ** 4,
             Type.i128,
             &.{ lhs_lsb, zero, rhs_msb, zero },
         );
         const mul2 = try func.callIntrinsic(
             "__multi3",
             &[_]InternPool.Index{.i64_type} ** 4,
             Type.i128,
             &.{ rhs_lsb, zero, lhs_msb, zero },
         );
         const mul3 = try func.callIntrinsic(
             "__multi3",
             &[_]InternPool.Index{.i64_type} ** 4,
             Type.i128,
             &.{ lhs_msb, zero, rhs_msb, zero },
         );
 
         const rhs_lsb_not_zero = try func.cmp(rhs_lsb, zero, Type.u64, .neq);
         const lhs_lsb_not_zero = try func.cmp(lhs_lsb, zero, Type.u64, .neq);
         const lsb_and = try func.binOp(rhs_lsb_not_zero, lhs_lsb_not_zero, Type.bool, .@"and");
         const mul1_lsb = try func.load(mul1, Type.u64, 8);
         const mul1_lsb_not_zero = try func.cmp(mul1_lsb, zero, Type.u64, .neq);
         const lsb_or1 = try func.binOp(lsb_and, mul1_lsb_not_zero, Type.bool, .@"or");
         const mul2_lsb = try func.load(mul2, Type.u64, 8);
         const mul2_lsb_not_zero = try func.cmp(mul2_lsb, zero, Type.u64, .neq);
         const lsb_or = try func.binOp(lsb_or1, mul2_lsb_not_zero, Type.bool, .@"or");
 
         const mul1_msb = try func.load(mul1, Type.u64, 0);
         const mul2_msb = try func.load(mul2, Type.u64, 0);
         const mul_add1 = try func.binOp(mul1_msb, mul2_msb, Type.u64, .add);
 
         var mul3_lsb = try (try func.load(mul3, Type.u64, 8)).toLocal(func, Type.u64);
         defer mul3_lsb.free(func);
         var mul_add2 = try (try func.binOp(mul_add1, mul3_lsb, Type.u64, .add)).toLocal(func, Type.u64);
         defer mul_add2.free(func);
         const mul_add_lt = try func.cmp(mul_add2, mul3_lsb, Type.u64, .lt);
 
         // result for overflow bit
         _ = try func.binOp(lsb_or, mul_add_lt, Type.bool, .@"or");
         try func.addLabel(.local_set, overflow_bit.local.value);
 
         const tmp_result = try func.allocStack(Type.u128);
         try func.emitWValue(tmp_result);
         const mul3_msb = try func.load(mul3, Type.u64, 0);
         try func.store(.stack, mul3_msb, Type.u64, tmp_result.offset());
         try func.store(tmp_result, mul_add2, Type.u64, 8);
         break :blk tmp_result;
     } else return func.fail("TODO: @mulWithOverflow for integers between 32 and 64 bits", .{});
     var bin_op_local = try bin_op.toLocal(func, lhs_ty);
     defer bin_op_local.free(func);
 
     const result_ptr = try func.allocStack(func.typeOfIndex(inst));
     try func.store(result_ptr, bin_op_local, lhs_ty, 0);
     const offset = @as(u32, @intCast(lhs_ty.abiSize(mod)));
     try func.store(result_ptr, overflow_bit, Type.u1, offset);
 
     func.finishAir(inst, result_ptr, &.{ extra.lhs, extra.rhs });
 }
 
 fn airMaxMin(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     assert(op == .max or op == .min);
     const mod = func.bin_file.base.comp.module.?;
     const target = mod.getTarget();
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ty = func.typeOfIndex(inst);
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: `@maximum` and `@minimum` for vectors", .{});
     }
 
     if (ty.abiSize(mod) > 16) {
         return func.fail("TODO: `@maximum` and `@minimum` for types larger than 16 bytes", .{});
     }
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     if (ty.zigTypeTag(mod) == .Float) {
         var fn_name_buf: [64]u8 = undefined;
         const float_bits = ty.floatBits(target);
         const fn_name = std.fmt.bufPrint(&fn_name_buf, "{s}f{s}{s}", .{
             target_util.libcFloatPrefix(float_bits),
             @tagName(op),
             target_util.libcFloatSuffix(float_bits),
         }) catch unreachable;
         const result = try func.callIntrinsic(fn_name, &.{ ty.ip_index, ty.ip_index }, ty, &.{ lhs, rhs });
         try func.lowerToStack(result);
     } else {
         // operands to select from
         try func.lowerToStack(lhs);
         try func.lowerToStack(rhs);
         _ = try func.cmp(lhs, rhs, ty, if (op == .max) .gt else .lt);
 
         // based on the result from comparison, return operand 0 or 1.
         try func.addTag(.select);
     }
 
     // store result in local
     const result_ty = if (isByRef(ty, mod)) Type.u32 else ty;
     const result = try func.allocLocal(result_ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airMulAdd(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const bin_op = func.air.extraData(Air.Bin, pl_op.payload).data;
 
     const ty = func.typeOfIndex(inst);
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: `@mulAdd` for vectors", .{});
     }
 
     const addend = try func.resolveInst(pl_op.operand);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     const result = if (ty.floatBits(func.target) == 16) fl_result: {
         const rhs_ext = try func.fpext(rhs, ty, Type.f32);
         const lhs_ext = try func.fpext(lhs, ty, Type.f32);
         const addend_ext = try func.fpext(addend, ty, Type.f32);
         // call to compiler-rt `fn fmaf(f32, f32, f32) f32`
         const result = try func.callIntrinsic(
             "fmaf",
             &.{ .f32_type, .f32_type, .f32_type },
             Type.f32,
             &.{ rhs_ext, lhs_ext, addend_ext },
         );
         break :fl_result try (try func.fptrunc(result, Type.f32, ty)).toLocal(func, ty);
     } else result: {
         const mul_result = try func.binOp(lhs, rhs, ty, .mul);
         break :result try (try func.binOp(mul_result, addend, ty, .add)).toLocal(func, ty);
     };
 
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs, pl_op.operand });
 }
 
 fn airClz(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const ty = func.typeOf(ty_op.operand);
     const result_ty = func.typeOfIndex(inst);
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: `@clz` for vectors", .{});
     }
 
     const operand = try func.resolveInst(ty_op.operand);
     const int_info = ty.intInfo(mod);
     const wasm_bits = toWasmBits(int_info.bits) orelse {
         return func.fail("TODO: `@clz` for integers with bitsize '{d}'", .{int_info.bits});
     };
 
     switch (wasm_bits) {
         32 => {
             try func.emitWValue(operand);
             try func.addTag(.i32_clz);
         },
         64 => {
             try func.emitWValue(operand);
             try func.addTag(.i64_clz);
             try func.addTag(.i32_wrap_i64);
         },
         128 => {
             var lsb = try (try func.load(operand, Type.u64, 8)).toLocal(func, Type.u64);
             defer lsb.free(func);
 
             try func.emitWValue(lsb);
             try func.addTag(.i64_clz);
             _ = try func.load(operand, Type.u64, 0);
             try func.addTag(.i64_clz);
             try func.emitWValue(.{ .imm64 = 64 });
             try func.addTag(.i64_add);
             _ = try func.cmp(lsb, .{ .imm64 = 0 }, Type.u64, .neq);
             try func.addTag(.select);
             try func.addTag(.i32_wrap_i64);
         },
         else => unreachable,
     }
 
     if (wasm_bits != int_info.bits) {
         try func.emitWValue(.{ .imm32 = wasm_bits - int_info.bits });
         try func.addTag(.i32_sub);
     }
 
     const result = try func.allocLocal(result_ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airCtz(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const ty = func.typeOf(ty_op.operand);
     const result_ty = func.typeOfIndex(inst);
 
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: `@ctz` for vectors", .{});
     }
 
     const operand = try func.resolveInst(ty_op.operand);
     const int_info = ty.intInfo(mod);
     const wasm_bits = toWasmBits(int_info.bits) orelse {
         return func.fail("TODO: `@clz` for integers with bitsize '{d}'", .{int_info.bits});
     };
 
     switch (wasm_bits) {
         32 => {
             if (wasm_bits != int_info.bits) {
                 const val: u32 = @as(u32, 1) << @as(u5, @intCast(int_info.bits));
                 // leave value on the stack
                 _ = try func.binOp(operand, .{ .imm32 = val }, ty, .@"or");
             } else try func.emitWValue(operand);
             try func.addTag(.i32_ctz);
         },
         64 => {
             if (wasm_bits != int_info.bits) {
                 const val: u64 = @as(u64, 1) << @as(u6, @intCast(int_info.bits));
                 // leave value on the stack
                 _ = try func.binOp(operand, .{ .imm64 = val }, ty, .@"or");
             } else try func.emitWValue(operand);
             try func.addTag(.i64_ctz);
             try func.addTag(.i32_wrap_i64);
         },
         128 => {
             var msb = try (try func.load(operand, Type.u64, 0)).toLocal(func, Type.u64);
             defer msb.free(func);
 
             try func.emitWValue(msb);
             try func.addTag(.i64_ctz);
             _ = try func.load(operand, Type.u64, 8);
             if (wasm_bits != int_info.bits) {
                 try func.addImm64(@as(u64, 1) << @as(u6, @intCast(int_info.bits - 64)));
                 try func.addTag(.i64_or);
             }
             try func.addTag(.i64_ctz);
             try func.addImm64(64);
             if (wasm_bits != int_info.bits) {
                 try func.addTag(.i64_or);
             } else {
                 try func.addTag(.i64_add);
             }
             _ = try func.cmp(msb, .{ .imm64 = 0 }, Type.u64, .neq);
             try func.addTag(.select);
             try func.addTag(.i32_wrap_i64);
         },
         else => unreachable,
     }
 
     const result = try func.allocLocal(result_ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airDbgVar(func: *CodeGen, inst: Air.Inst.Index, is_ptr: bool) !void {
     if (func.debug_output != .dwarf) return func.finishAir(inst, .none, &.{});
 
     const mod = func.bin_file.base.comp.module.?;
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const ty = func.typeOf(pl_op.operand);
     const operand = try func.resolveInst(pl_op.operand);
 
     log.debug("airDbgVar: %{d}: {}, {}", .{ inst, ty.fmtDebug(), operand });
 
     const name = func.air.nullTerminatedString(pl_op.payload);
     log.debug(" var name = ({s})", .{name});
 
     const loc: link.File.Dwarf.DeclState.DbgInfoLoc = switch (operand) {
         .local => |local| .{ .wasm_local = local.value },
         else => blk: {
             log.debug("TODO generate debug info for {}", .{operand});
             break :blk .nop;
         },
     };
     try func.debug_output.dwarf.genVarDbgInfo(name, ty, mod.funcOwnerDeclIndex(func.func_index), is_ptr, loc);
 
     func.finishAir(inst, .none, &.{});
 }
 
 fn airDbgStmt(func: *CodeGen, inst: Air.Inst.Index) !void {
     if (func.debug_output != .dwarf) return func.finishAir(inst, .none, &.{});
 
     const dbg_stmt = func.air.instructions.items(.data)[@intFromEnum(inst)].dbg_stmt;
     try func.addInst(.{ .tag = .dbg_line, .data = .{
         .payload = try func.addExtra(Mir.DbgLineColumn{
             .line = dbg_stmt.line,
             .column = dbg_stmt.column,
         }),
     } });
     func.finishAir(inst, .none, &.{});
 }
 
 fn airTry(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const err_union = try func.resolveInst(pl_op.operand);
     const extra = func.air.extraData(Air.Try, pl_op.payload);
     const body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra.end..][0..extra.data.body_len]);
     const err_union_ty = func.typeOf(pl_op.operand);
     const result = try lowerTry(func, inst, err_union, body, err_union_ty, false);
     func.finishAir(inst, result, &.{pl_op.operand});
 }
 
 fn airTryPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.TryPtr, ty_pl.payload);
     const err_union_ptr = try func.resolveInst(extra.data.ptr);
     const body: []const Air.Inst.Index = @ptrCast(func.air.extra[extra.end..][0..extra.data.body_len]);
     const err_union_ty = func.typeOf(extra.data.ptr).childType(mod);
     const result = try lowerTry(func, inst, err_union_ptr, body, err_union_ty, true);
     func.finishAir(inst, result, &.{extra.data.ptr});
 }
 
 fn lowerTry(
     func: *CodeGen,
     inst: Air.Inst.Index,
     err_union: WValue,
     body: []const Air.Inst.Index,
     err_union_ty: Type,
     operand_is_ptr: bool,
 ) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     if (operand_is_ptr) {
         return func.fail("TODO: lowerTry for pointers", .{});
     }
 
     const pl_ty = err_union_ty.errorUnionPayload(mod);
     const pl_has_bits = pl_ty.hasRuntimeBitsIgnoreComptime(mod);
 
     if (!err_union_ty.errorUnionSet(mod).errorSetIsEmpty(mod)) {
         // Block we can jump out of when error is not set
         try func.startBlock(.block, wasm.block_empty);
 
         // check if the error tag is set for the error union.
         try func.emitWValue(err_union);
         if (pl_has_bits) {
             const err_offset = @as(u32, @intCast(errUnionErrorOffset(pl_ty, mod)));
             try func.addMemArg(.i32_load16_u, .{
                 .offset = err_union.offset() + err_offset,
                 .alignment = @intCast(Type.anyerror.abiAlignment(mod).toByteUnitsOptional().?),
             });
         }
         try func.addTag(.i32_eqz);
         try func.addLabel(.br_if, 0); // jump out of block when error is '0'
 
         const liveness = func.liveness.getCondBr(inst);
         try func.branches.append(func.gpa, .{});
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.else_deaths.len + liveness.then_deaths.len);
         defer {
             var branch = func.branches.pop();
             branch.deinit(func.gpa);
         }
         try func.genBody(body);
         try func.endBlock();
     }
 
     // if we reach here it means error was not set, and we want the payload
     if (!pl_has_bits) {
         return WValue{ .none = {} };
     }
 
     const pl_offset = @as(u32, @intCast(errUnionPayloadOffset(pl_ty, mod)));
     if (isByRef(pl_ty, mod)) {
         return buildPointerOffset(func, err_union, pl_offset, .new);
     }
     const payload = try func.load(err_union, pl_ty, pl_offset);
     return payload.toLocal(func, pl_ty);
 }
 
 fn airByteSwap(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const ty = func.typeOfIndex(inst);
     const operand = try func.resolveInst(ty_op.operand);
 
     if (ty.zigTypeTag(mod) == .Vector) {
         return func.fail("TODO: @byteSwap for vectors", .{});
     }
     const int_info = ty.intInfo(mod);
 
     // bytes are no-op
     if (int_info.bits == 8) {
         return func.finishAir(inst, func.reuseOperand(ty_op.operand, operand), &.{ty_op.operand});
     }
 
     const result = result: {
         switch (int_info.bits) {
             16 => {
                 const shl_res = try func.binOp(operand, .{ .imm32 = 8 }, ty, .shl);
                 const lhs = try func.binOp(shl_res, .{ .imm32 = 0xFF00 }, ty, .@"and");
                 const shr_res = try func.binOp(operand, .{ .imm32 = 8 }, ty, .shr);
                 const res = if (int_info.signedness == .signed) blk: {
                     break :blk try func.wrapOperand(shr_res, Type.u8);
                 } else shr_res;
                 break :result try (try func.binOp(lhs, res, ty, .@"or")).toLocal(func, ty);
             },
             24 => {
                 var msb = try (try func.wrapOperand(operand, Type.u16)).toLocal(func, Type.u16);
                 defer msb.free(func);
 
                 const shl_res = try func.binOp(msb, .{ .imm32 = 8 }, Type.u16, .shl);
                 const lhs = try func.binOp(shl_res, .{ .imm32 = 0xFF0000 }, Type.u16, .@"and");
                 const shr_res = try func.binOp(msb, .{ .imm32 = 8 }, ty, .shr);
 
                 const res = if (int_info.signedness == .signed) blk: {
                     break :blk try func.wrapOperand(shr_res, Type.u8);
                 } else shr_res;
                 const lhs_tmp = try func.binOp(lhs, res, ty, .@"or");
                 const lhs_result = try func.binOp(lhs_tmp, .{ .imm32 = 8 }, ty, .shr);
                 const rhs_wrap = try func.wrapOperand(msb, Type.u8);
                 const rhs_result = try func.binOp(rhs_wrap, .{ .imm32 = 16 }, ty, .shl);
 
                 const lsb = try func.wrapBinOp(operand, .{ .imm32 = 16 }, Type.u8, .shr);
                 const tmp = try func.binOp(lhs_result, rhs_result, ty, .@"or");
                 break :result try (try func.binOp(tmp, lsb, ty, .@"or")).toLocal(func, ty);
             },
             32 => {
                 const shl_tmp = try func.binOp(operand, .{ .imm32 = 8 }, ty, .shl);
                 var lhs = try (try func.binOp(shl_tmp, .{ .imm32 = 0xFF00FF00 }, ty, .@"and")).toLocal(func, ty);
                 defer lhs.free(func);
                 const shr_tmp = try func.binOp(operand, .{ .imm32 = 8 }, ty, .shr);
                 var rhs = try (try func.binOp(shr_tmp, .{ .imm32 = 0xFF00FF }, ty, .@"and")).toLocal(func, ty);
                 defer rhs.free(func);
                 var tmp_or = try (try func.binOp(lhs, rhs, ty, .@"or")).toLocal(func, ty);
                 defer tmp_or.free(func);
 
                 const shl = try func.binOp(tmp_or, .{ .imm32 = 16 }, ty, .shl);
                 const shr = try func.binOp(tmp_or, .{ .imm32 = 16 }, ty, .shr);
                 const res = if (int_info.signedness == .signed) blk: {
                     break :blk try func.wrapOperand(shr, Type.u16);
                 } else shr;
                 break :result try (try func.binOp(shl, res, ty, .@"or")).toLocal(func, ty);
             },
             else => return func.fail("TODO: @byteSwap for integers with bitsize {d}", .{int_info.bits}),
         }
     };
     func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 fn airDiv(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ty = func.typeOfIndex(inst);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     const result = if (ty.isSignedInt(mod))
         try func.divSigned(lhs, rhs, ty)
     else
         try (try func.binOp(lhs, rhs, ty, .div)).toLocal(func, ty);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airDivTrunc(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ty = func.typeOfIndex(inst);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     const div_result = if (ty.isSignedInt(mod))
         try func.divSigned(lhs, rhs, ty)
     else
         try (try func.binOp(lhs, rhs, ty, .div)).toLocal(func, ty);
 
     if (ty.isAnyFloat()) {
         const trunc_result = try (try func.floatOp(.trunc, ty, &.{div_result})).toLocal(func, ty);
         return func.finishAir(inst, trunc_result, &.{ bin_op.lhs, bin_op.rhs });
     }
 
     return func.finishAir(inst, div_result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airDivFloor(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const mod = func.bin_file.base.comp.module.?;
     const ty = func.typeOfIndex(inst);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     if (ty.isUnsignedInt(mod)) {
         _ = try func.binOp(lhs, rhs, ty, .div);
     } else if (ty.isSignedInt(mod)) {
         const int_bits = ty.intInfo(mod).bits;
         const wasm_bits = toWasmBits(int_bits) orelse {
             return func.fail("TODO: `@divFloor` for signed integers larger than 64 bits ({d} bits requested)", .{int_bits});
         };
 
         if (wasm_bits > 64) {
             return func.fail("TODO: `@divFloor` for signed integers larger than 64 bits ({d} bits requested)", .{int_bits});
         }
 
         const lhs_wasm = if (wasm_bits != int_bits)
             try (try func.signExtendInt(lhs, ty)).toLocal(func, ty)
         else
             lhs;
 
         const rhs_wasm = if (wasm_bits != int_bits)
             try (try func.signExtendInt(rhs, ty)).toLocal(func, ty)
         else
             rhs;
 
         const zero = switch (wasm_bits) {
             32 => WValue{ .imm32 = 0 },
             64 => WValue{ .imm64 = 0 },
             else => unreachable,
         };
 
         // tee leaves the value on the stack and stores it in a local.
         const quotient = try func.allocLocal(ty);
         _ = try func.binOp(lhs_wasm, rhs_wasm, ty, .div);
         try func.addLabel(.local_tee, quotient.local.value);
 
         // select takes a 32 bit value as the condition, so in the 64 bit case we use eqz to narrow
         // the 64 bit value we want to use as the condition to 32 bits.
         // This also inverts the condition (non 0 => 0, 0 => 1), so we put the adjusted and
         // non-adjusted quotients on the stack in the opposite order for 32 vs 64 bits.
         if (wasm_bits == 64) {
             try func.emitWValue(quotient);
         }
 
         // 0 if the signs of rhs_wasm and lhs_wasm are the same, 1 otherwise.
         _ = try func.binOp(lhs_wasm, rhs_wasm, ty, .xor);
         _ = try func.cmp(.stack, zero, ty, .lt);
 
         switch (wasm_bits) {
             32 => {
                 try func.addTag(.i32_sub);
                 try func.emitWValue(quotient);
             },
             64 => {
                 try func.addTag(.i64_extend_i32_u);
                 try func.addTag(.i64_sub);
             },
             else => unreachable,
         }
 
         _ = try func.binOp(lhs_wasm, rhs_wasm, ty, .rem);
 
         if (wasm_bits == 64) {
             try func.addTag(.i64_eqz);
         }
 
         try func.addTag(.select);
 
         // We need to zero the high bits because N bit comparisons consider all 32 or 64 bits, and
         // expect all but the lowest N bits to be 0.
         // TODO: Should we be zeroing the high bits here or should we be ignoring the high bits
         // when performing comparisons?
         if (int_bits != wasm_bits) {
             _ = try func.wrapOperand(.{ .stack = {} }, ty);
         }
     } else {
         const float_bits = ty.floatBits(func.target);
         if (float_bits > 64) {
             return func.fail("TODO: `@divFloor` for floats with bitsize: {d}", .{float_bits});
         }
         const is_f16 = float_bits == 16;
 
         const lhs_wasm = if (is_f16) try func.fpext(lhs, Type.f16, Type.f32) else lhs;
         const rhs_wasm = if (is_f16) try func.fpext(rhs, Type.f16, Type.f32) else rhs;
 
         try func.emitWValue(lhs_wasm);
         try func.emitWValue(rhs_wasm);
 
         switch (float_bits) {
             16, 32 => {
                 try func.addTag(.f32_div);
                 try func.addTag(.f32_floor);
             },
             64 => {
                 try func.addTag(.f64_div);
                 try func.addTag(.f64_floor);
             },
             else => unreachable,
         }
 
         if (is_f16) {
             _ = try func.fptrunc(.{ .stack = {} }, Type.f32, Type.f16);
         }
     }
 
     const result = try func.allocLocal(ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn divSigned(func: *CodeGen, lhs: WValue, rhs: WValue, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const int_bits = ty.intInfo(mod).bits;
     const wasm_bits = toWasmBits(int_bits) orelse {
         return func.fail("TODO: Implement signed division for integers with bitsize '{d}'", .{int_bits});
     };
 
     if (wasm_bits == 128) {
         return func.fail("TODO: Implement signed division for 128-bit integerrs", .{});
     }
 
     if (wasm_bits != int_bits) {
         // Leave both values on the stack
         _ = try func.signExtendInt(lhs, ty);
         _ = try func.signExtendInt(rhs, ty);
     } else {
         try func.emitWValue(lhs);
         try func.emitWValue(rhs);
     }
     try func.addTag(.i32_div_s);
 
     const result = try func.allocLocal(ty);
     try func.addLabel(.local_set, result.local.value);
     return result;
 }
 
 /// Remainder after floor division, defined by:
 /// @divFloor(a, b) * b + @mod(a, b) = a
 fn airMod(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const mod = func.bin_file.base.comp.module.?;
     const ty = func.typeOfIndex(inst);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     if (ty.isUnsignedInt(mod)) {
         _ = try func.binOp(lhs, rhs, ty, .rem);
     } else if (ty.isSignedInt(mod)) {
         // The wasm rem instruction gives the remainder after truncating division (rounding towards
         // 0), equivalent to @rem.
         // We make use of the fact that:
         // @mod(a, b) = @rem(@rem(a, b) + b, b)
         const int_bits = ty.intInfo(mod).bits;
         const wasm_bits = toWasmBits(int_bits) orelse {
             return func.fail("TODO: `@mod` for signed integers larger than 64 bits ({d} bits requested)", .{int_bits});
         };
 
         if (wasm_bits > 64) {
             return func.fail("TODO: `@mod` for signed integers larger than 64 bits ({d} bits requested)", .{int_bits});
         }
 
         const lhs_wasm = if (wasm_bits != int_bits)
             try (try func.signExtendInt(lhs, ty)).toLocal(func, ty)
         else
             lhs;
 
         const rhs_wasm = if (wasm_bits != int_bits)
             try (try func.signExtendInt(rhs, ty)).toLocal(func, ty)
         else
             rhs;
 
         _ = try func.binOp(lhs_wasm, rhs_wasm, ty, .rem);
         _ = try func.binOp(.stack, rhs_wasm, ty, .add);
         _ = try func.binOp(.stack, rhs_wasm, ty, .rem);
     } else {
         return func.fail("TODO: implement `@mod` on floating point types for {}", .{func.target.cpu.arch});
     }
 
     const result = try func.allocLocal(ty);
     try func.addLabel(.local_set, result.local.value);
     func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Sign extends an N bit signed integer and pushes the result to the stack.
 /// The result will be sign extended to 32 bits if N <= 32 or 64 bits if N <= 64.
 /// Support for integers wider than 64 bits has not yet been implemented.
 fn signExtendInt(func: *CodeGen, operand: WValue, ty: Type) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const int_bits = ty.intInfo(mod).bits;
     const wasm_bits = toWasmBits(int_bits) orelse {
         return func.fail("TODO: signExtendInt for signed integers larger than '{d}' bits", .{int_bits});
     };
 
     const shift_val = switch (wasm_bits) {
         32 => WValue{ .imm32 = wasm_bits - int_bits },
         64 => WValue{ .imm64 = wasm_bits - int_bits },
         else => return func.fail("TODO: signExtendInt for i128", .{}),
     };
 
     try func.emitWValue(operand);
     switch (wasm_bits) {
         32 => {
             try func.emitWValue(shift_val);
             try func.addTag(.i32_shl);
             try func.emitWValue(shift_val);
             try func.addTag(.i32_shr_s);
         },
         64 => {
             try func.emitWValue(shift_val);
             try func.addTag(.i64_shl);
             try func.emitWValue(shift_val);
             try func.addTag(.i64_shr_s);
         },
         else => unreachable,
     }
 
     return WValue{ .stack = {} };
 }
 
 fn airSatBinOp(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
     assert(op == .add or op == .sub);
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const mod = func.bin_file.base.comp.module.?;
     const ty = func.typeOfIndex(inst);
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
 
     const int_info = ty.intInfo(mod);
     const is_signed = int_info.signedness == .signed;
 
     if (int_info.bits > 64) {
         return func.fail("TODO: saturating arithmetic for integers with bitsize '{d}'", .{int_info.bits});
     }
 
     if (is_signed) {
         const result = try signedSat(func, lhs, rhs, ty, op);
         return func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
     }
 
     const wasm_bits = toWasmBits(int_info.bits).?;
     var bin_result = try (try func.binOp(lhs, rhs, ty, op)).toLocal(func, ty);
     defer bin_result.free(func);
     if (wasm_bits != int_info.bits and op == .add) {
         const val: u64 = @as(u64, @intCast((@as(u65, 1) << @as(u7, @intCast(int_info.bits))) - 1));
         const imm_val = switch (wasm_bits) {
             32 => WValue{ .imm32 = @as(u32, @intCast(val)) },
             64 => WValue{ .imm64 = val },
             else => unreachable,
         };
 
         try func.emitWValue(bin_result);
         try func.emitWValue(imm_val);
         _ = try func.cmp(bin_result, imm_val, ty, .lt);
     } else {
         switch (wasm_bits) {
             32 => try func.addImm32(if (op == .add) @as(i32, -1) else 0),
             64 => try func.addImm64(if (op == .add) @as(u64, @bitCast(@as(i64, -1))) else 0),
             else => unreachable,
         }
         try func.emitWValue(bin_result);
         _ = try func.cmp(bin_result, lhs, ty, if (op == .add) .lt else .gt);
     }
 
     try func.addTag(.select);
     const result = try func.allocLocal(ty);
     try func.addLabel(.local_set, result.local.value);
     return func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn signedSat(func: *CodeGen, lhs_operand: WValue, rhs_operand: WValue, ty: Type, op: Op) InnerError!WValue {
     const mod = func.bin_file.base.comp.module.?;
     const int_info = ty.intInfo(mod);
     const wasm_bits = toWasmBits(int_info.bits).?;
     const is_wasm_bits = wasm_bits == int_info.bits;
     const ext_ty = if (!is_wasm_bits) try mod.intType(int_info.signedness, wasm_bits) else ty;
 
     var lhs = if (!is_wasm_bits) lhs: {
         break :lhs try (try func.signExtendInt(lhs_operand, ty)).toLocal(func, ext_ty);
     } else lhs_operand;
     var rhs = if (!is_wasm_bits) rhs: {
         break :rhs try (try func.signExtendInt(rhs_operand, ty)).toLocal(func, ext_ty);
     } else rhs_operand;
 
     const max_val: u64 = @as(u64, @intCast((@as(u65, 1) << @as(u7, @intCast(int_info.bits - 1))) - 1));
     const min_val: i64 = (-@as(i64, @intCast(@as(u63, @intCast(max_val))))) - 1;
     const max_wvalue = switch (wasm_bits) {
         32 => WValue{ .imm32 = @as(u32, @truncate(max_val)) },
         64 => WValue{ .imm64 = max_val },
         else => unreachable,
     };
     const min_wvalue = switch (wasm_bits) {
         32 => WValue{ .imm32 = @as(u32, @bitCast(@as(i32, @truncate(min_val)))) },
         64 => WValue{ .imm64 = @as(u64, @bitCast(min_val)) },
         else => unreachable,
     };
 
     var bin_result = try (try func.binOp(lhs, rhs, ext_ty, op)).toLocal(func, ext_ty);
     if (!is_wasm_bits) {
         defer bin_result.free(func); // not returned in this branch
         defer lhs.free(func); // uses temporary local for absvalue
         defer rhs.free(func); // uses temporary local for absvalue
         try func.emitWValue(bin_result);
         try func.emitWValue(max_wvalue);
         _ = try func.cmp(bin_result, max_wvalue, ext_ty, .lt);
         try func.addTag(.select);
         try func.addLabel(.local_set, bin_result.local.value); // re-use local
 
         try func.emitWValue(bin_result);
         try func.emitWValue(min_wvalue);
         _ = try func.cmp(bin_result, min_wvalue, ext_ty, .gt);
         try func.addTag(.select);
         try func.addLabel(.local_set, bin_result.local.value); // re-use local
         return (try func.wrapOperand(bin_result, ty)).toLocal(func, ty);
     } else {
         const zero = switch (wasm_bits) {
             32 => WValue{ .imm32 = 0 },
             64 => WValue{ .imm64 = 0 },
             else => unreachable,
         };
         try func.emitWValue(max_wvalue);
         try func.emitWValue(min_wvalue);
         _ = try func.cmp(bin_result, zero, ty, .lt);
         try func.addTag(.select);
         try func.emitWValue(bin_result);
         // leave on stack
         const cmp_zero_result = try func.cmp(rhs, zero, ty, if (op == .add) .lt else .gt);
         const cmp_bin_result = try func.cmp(bin_result, lhs, ty, .lt);
         _ = try func.binOp(cmp_zero_result, cmp_bin_result, Type.u32, .xor); // comparisons always return i32, so provide u32 as type to xor.
         try func.addTag(.select);
         try func.addLabel(.local_set, bin_result.local.value); // re-use local
         return bin_result;
     }
 }
 
 fn airShlSat(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const mod = func.bin_file.base.comp.module.?;
     const ty = func.typeOfIndex(inst);
     const int_info = ty.intInfo(mod);
     const is_signed = int_info.signedness == .signed;
     if (int_info.bits > 64) {
         return func.fail("TODO: Saturating shifting left for integers with bitsize '{d}'", .{int_info.bits});
     }
 
     const lhs = try func.resolveInst(bin_op.lhs);
     const rhs = try func.resolveInst(bin_op.rhs);
     const wasm_bits = toWasmBits(int_info.bits).?;
     const result = try func.allocLocal(ty);
 
     if (wasm_bits == int_info.bits) outer_blk: {
         var shl = try (try func.binOp(lhs, rhs, ty, .shl)).toLocal(func, ty);
         defer shl.free(func);
         var shr = try (try func.binOp(shl, rhs, ty, .shr)).toLocal(func, ty);
         defer shr.free(func);
 
         switch (wasm_bits) {
             32 => blk: {
                 if (!is_signed) {
                     try func.addImm32(-1);
                     break :blk;
                 }
                 try func.addImm32(std.math.minInt(i32));
                 try func.addImm32(std.math.maxInt(i32));
                 _ = try func.cmp(lhs, .{ .imm32 = 0 }, ty, .lt);
                 try func.addTag(.select);
             },
             64 => blk: {
                 if (!is_signed) {
                     try func.addImm64(@as(u64, @bitCast(@as(i64, -1))));
                     break :blk;
                 }
                 try func.addImm64(@as(u64, @bitCast(@as(i64, std.math.minInt(i64)))));
                 try func.addImm64(@as(u64, @bitCast(@as(i64, std.math.maxInt(i64)))));
                 _ = try func.cmp(lhs, .{ .imm64 = 0 }, ty, .lt);
                 try func.addTag(.select);
             },
             else => unreachable,
         }
         try func.emitWValue(shl);
         _ = try func.cmp(lhs, shr, ty, .neq);
         try func.addTag(.select);
         try func.addLabel(.local_set, result.local.value);
         break :outer_blk;
     } else {
         const shift_size = wasm_bits - int_info.bits;
         const shift_value = switch (wasm_bits) {
             32 => WValue{ .imm32 = shift_size },
             64 => WValue{ .imm64 = shift_size },
             else => unreachable,
         };
         const ext_ty = try mod.intType(int_info.signedness, wasm_bits);
 
         var shl_res = try (try func.binOp(lhs, shift_value, ext_ty, .shl)).toLocal(func, ext_ty);
         defer shl_res.free(func);
         var shl = try (try func.binOp(shl_res, rhs, ext_ty, .shl)).toLocal(func, ext_ty);
         defer shl.free(func);
         var shr = try (try func.binOp(shl, rhs, ext_ty, .shr)).toLocal(func, ext_ty);
         defer shr.free(func);
 
         switch (wasm_bits) {
             32 => blk: {
                 if (!is_signed) {
                     try func.addImm32(-1);
                     break :blk;
                 }
 
                 try func.addImm32(std.math.minInt(i32));
                 try func.addImm32(std.math.maxInt(i32));
                 _ = try func.cmp(shl_res, .{ .imm32 = 0 }, ext_ty, .lt);
                 try func.addTag(.select);
             },
             64 => blk: {
                 if (!is_signed) {
                     try func.addImm64(@as(u64, @bitCast(@as(i64, -1))));
                     break :blk;
                 }
 
                 try func.addImm64(@as(u64, @bitCast(@as(i64, std.math.minInt(i64)))));
                 try func.addImm64(@as(u64, @bitCast(@as(i64, std.math.maxInt(i64)))));
                 _ = try func.cmp(shl_res, .{ .imm64 = 0 }, ext_ty, .lt);
                 try func.addTag(.select);
             },
             else => unreachable,
         }
         try func.emitWValue(shl);
         _ = try func.cmp(shl_res, shr, ext_ty, .neq);
         try func.addTag(.select);
         try func.addLabel(.local_set, result.local.value);
         var shift_result = try func.binOp(result, shift_value, ext_ty, .shr);
         if (is_signed) {
             shift_result = try func.wrapOperand(shift_result, ty);
         }
         try func.addLabel(.local_set, result.local.value);
     }
 
     return func.finishAir(inst, result, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 /// Calls a compiler-rt intrinsic by creating an undefined symbol,
 /// then lowering the arguments and calling the symbol as a function call.
 /// This function call assumes the C-ABI.
 /// Asserts arguments are not stack values when the return value is
 /// passed as the first parameter.
 /// May leave the return value on the stack.
 fn callIntrinsic(
     func: *CodeGen,
     name: []const u8,
     param_types: []const InternPool.Index,
     return_type: Type,
     args: []const WValue,
 ) InnerError!WValue {
     assert(param_types.len == args.len);
     const symbol_index = func.bin_file.base.getGlobalSymbol(name, null) catch |err| {
         return func.fail("Could not find or create global symbol '{s}'", .{@errorName(err)});
     };
 
     // Always pass over C-ABI
     const mod = func.bin_file.base.comp.module.?;
     var func_type = try genFunctype(func.gpa, .C, param_types, return_type, mod);
     defer func_type.deinit(func.gpa);
     const func_type_index = try func.bin_file.putOrGetFuncType(func_type);
     try func.bin_file.addOrUpdateImport(name, symbol_index, null, func_type_index);
 
     const want_sret_param = firstParamSRet(.C, return_type, mod);
     // if we want return as first param, we allocate a pointer to stack,
     // and emit it as our first argument
     const sret = if (want_sret_param) blk: {
         const sret_local = try func.allocStack(return_type);
         try func.lowerToStack(sret_local);
         break :blk sret_local;
     } else WValue{ .none = {} };
 
     // Lower all arguments to the stack before we call our function
     for (args, 0..) |arg, arg_i| {
         assert(!(want_sret_param and arg == .stack));
         assert(Type.fromInterned(param_types[arg_i]).hasRuntimeBitsIgnoreComptime(mod));
         try func.lowerArg(.C, Type.fromInterned(param_types[arg_i]), arg);
     }
 
     // Actually call our intrinsic
     try func.addLabel(.call, symbol_index);
 
     if (!return_type.hasRuntimeBitsIgnoreComptime(mod)) {
         return WValue.none;
     } else if (return_type.isNoReturn(mod)) {
         try func.addTag(.@"unreachable");
         return WValue.none;
     } else if (want_sret_param) {
         return sret;
     } else {
         return WValue{ .stack = {} };
     }
 }
 
 fn airTagName(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const un_op = func.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
     const operand = try func.resolveInst(un_op);
     const enum_ty = func.typeOf(un_op);
 
     const func_sym_index = try func.getTagNameFunction(enum_ty);
 
     const result_ptr = try func.allocStack(func.typeOfIndex(inst));
     try func.lowerToStack(result_ptr);
     try func.emitWValue(operand);
     try func.addLabel(.call, func_sym_index);
 
     return func.finishAir(inst, result_ptr, &.{un_op});
 }
 
 fn getTagNameFunction(func: *CodeGen, enum_ty: Type) InnerError!u32 {
     const mod = func.bin_file.base.comp.module.?;
     const enum_decl_index = enum_ty.getOwnerDecl(mod);
 
     var arena_allocator = std.heap.ArenaAllocator.init(func.gpa);
     defer arena_allocator.deinit();
     const arena = arena_allocator.allocator();
 
     const fqn = mod.intern_pool.stringToSlice(try mod.declPtr(enum_decl_index).getFullyQualifiedName(mod));
     const func_name = try std.fmt.allocPrintZ(arena, "__zig_tag_name_{s}", .{fqn});
 
     // check if we already generated code for this.
     if (func.bin_file.findGlobalSymbol(func_name)) |loc| {
         return loc.index;
     }
 
     const int_tag_ty = enum_ty.intTagType(mod);
 
     if (int_tag_ty.bitSize(mod) > 64) {
         return func.fail("TODO: Implement @tagName for enums with tag size larger than 64 bits", .{});
     }
 
     var relocs = std.ArrayList(link.File.Wasm.Relocation).init(func.gpa);
     defer relocs.deinit();
 
     var body_list = std.ArrayList(u8).init(func.gpa);
     defer body_list.deinit();
     var writer = body_list.writer();
 
     // The locals of the function body (always 0)
     try leb.writeULEB128(writer, @as(u32, 0));
 
     // outer block
     try writer.writeByte(std.wasm.opcode(.block));
     try writer.writeByte(std.wasm.block_empty);
 
     // TODO: Make switch implementation generic so we can use a jump table for this when the tags are not sparse.
     // generate an if-else chain for each tag value as well as constant.
     for (enum_ty.enumFields(mod), 0..) |tag_name_ip, field_index_usize| {
         const field_index = @as(u32, @intCast(field_index_usize));
         const tag_name = mod.intern_pool.stringToSlice(tag_name_ip);
         // for each tag name, create an unnamed const,
         // and then get a pointer to its value.
         const name_ty = try mod.arrayType(.{
             .len = tag_name.len,
             .child = .u8_type,
             .sentinel = .zero_u8,
         });
         const name_val = try mod.intern(.{ .aggregate = .{
             .ty = name_ty.toIntern(),
             .storage = .{ .bytes = tag_name },
         } });
         const tag_sym_index = try func.bin_file.lowerUnnamedConst(
             .{ .ty = name_ty, .val = Value.fromInterned(name_val) },
             enum_decl_index,
         );
 
         // block for this if case
         try writer.writeByte(std.wasm.opcode(.block));
         try writer.writeByte(std.wasm.block_empty);
 
         // get actual tag value (stored in 2nd parameter);
         try writer.writeByte(std.wasm.opcode(.local_get));
         try leb.writeULEB128(writer, @as(u32, 1));
 
         const tag_val = try mod.enumValueFieldIndex(enum_ty, field_index);
         const tag_value = try func.lowerConstant(tag_val, enum_ty);
 
         switch (tag_value) {
             .imm32 => |value| {
                 try writer.writeByte(std.wasm.opcode(.i32_const));
                 try leb.writeILEB128(writer, @as(i32, @bitCast(value)));
                 try writer.writeByte(std.wasm.opcode(.i32_ne));
             },
             .imm64 => |value| {
                 try writer.writeByte(std.wasm.opcode(.i64_const));
                 try leb.writeILEB128(writer, @as(i64, @bitCast(value)));
                 try writer.writeByte(std.wasm.opcode(.i64_ne));
             },
             else => unreachable,
         }
         // if they're not equal, break out of current branch
         try writer.writeByte(std.wasm.opcode(.br_if));
         try leb.writeULEB128(writer, @as(u32, 0));
 
         // store the address of the tagname in the pointer field of the slice
         // get the address twice so we can also store the length.
         try writer.writeByte(std.wasm.opcode(.local_get));
         try leb.writeULEB128(writer, @as(u32, 0));
         try writer.writeByte(std.wasm.opcode(.local_get));
         try leb.writeULEB128(writer, @as(u32, 0));
 
         // get address of tagname and emit a relocation to it
         if (func.arch() == .wasm32) {
             const encoded_alignment = @ctz(@as(u32, 4));
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try relocs.append(.{
                 .relocation_type = .R_WASM_MEMORY_ADDR_LEB,
                 .offset = @as(u32, @intCast(body_list.items.len)),
                 .index = tag_sym_index,
             });
             try writer.writeAll(&[_]u8{0} ** 5); // will be relocated
 
             // store pointer
             try writer.writeByte(std.wasm.opcode(.i32_store));
             try leb.writeULEB128(writer, encoded_alignment);
             try leb.writeULEB128(writer, @as(u32, 0));
 
             // store length
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try leb.writeULEB128(writer, @as(u32, @intCast(tag_name.len)));
             try writer.writeByte(std.wasm.opcode(.i32_store));
             try leb.writeULEB128(writer, encoded_alignment);
             try leb.writeULEB128(writer, @as(u32, 4));
         } else {
             const encoded_alignment = @ctz(@as(u32, 8));
             try writer.writeByte(std.wasm.opcode(.i64_const));
             try relocs.append(.{
                 .relocation_type = .R_WASM_MEMORY_ADDR_LEB64,
                 .offset = @as(u32, @intCast(body_list.items.len)),
                 .index = tag_sym_index,
             });
             try writer.writeAll(&[_]u8{0} ** 10); // will be relocated
 
             // store pointer
             try writer.writeByte(std.wasm.opcode(.i64_store));
             try leb.writeULEB128(writer, encoded_alignment);
             try leb.writeULEB128(writer, @as(u32, 0));
 
             // store length
             try writer.writeByte(std.wasm.opcode(.i64_const));
             try leb.writeULEB128(writer, @as(u64, @intCast(tag_name.len)));
             try writer.writeByte(std.wasm.opcode(.i64_store));
             try leb.writeULEB128(writer, encoded_alignment);
             try leb.writeULEB128(writer, @as(u32, 8));
         }
 
         // break outside blocks
         try writer.writeByte(std.wasm.opcode(.br));
         try leb.writeULEB128(writer, @as(u32, 1));
 
         // end the block for this case
         try writer.writeByte(std.wasm.opcode(.end));
     }
 
     try writer.writeByte(std.wasm.opcode(.@"unreachable")); // tag value does not have a name
     // finish outer block
     try writer.writeByte(std.wasm.opcode(.end));
     // finish function body
     try writer.writeByte(std.wasm.opcode(.end));
 
     const slice_ty = Type.slice_const_u8_sentinel_0;
     const func_type = try genFunctype(arena, .Unspecified, &.{int_tag_ty.ip_index}, slice_ty, mod);
     return func.bin_file.createFunction(func_name, func_type, &body_list, &relocs);
 }
 
 fn airErrorSetHasValue(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_op = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
     const operand = try func.resolveInst(ty_op.operand);
     const error_set_ty = ty_op.ty.toType();
     const result = try func.allocLocal(Type.bool);
 
     const names = error_set_ty.errorSetNames(mod);
     var values = try std.ArrayList(u32).initCapacity(func.gpa, names.len);
     defer values.deinit();
 
     var lowest: ?u32 = null;
     var highest: ?u32 = null;
     for (names) |name| {
         const err_int = @as(Module.ErrorInt, @intCast(mod.global_error_set.getIndex(name).?));
         if (lowest) |*l| {
             if (err_int < l.*) {
                 l.* = err_int;
             }
         } else {
             lowest = err_int;
         }
         if (highest) |*h| {
             if (err_int > h.*) {
                 highest = err_int;
             }
         } else {
             highest = err_int;
         }
 
         values.appendAssumeCapacity(err_int);
     }
 
     // start block for 'true' branch
     try func.startBlock(.block, wasm.block_empty);
     // start block for 'false' branch
     try func.startBlock(.block, wasm.block_empty);
     // block for the jump table itself
     try func.startBlock(.block, wasm.block_empty);
 
     // lower operand to determine jump table target
     try func.emitWValue(operand);
     try func.addImm32(@as(i32, @intCast(lowest.?)));
     try func.addTag(.i32_sub);
 
     // Account for default branch so always add '1'
     const depth = @as(u32, @intCast(highest.? - lowest.? + 1));
     const jump_table: Mir.JumpTable = .{ .length = depth };
     const table_extra_index = try func.addExtra(jump_table);
     try func.addInst(.{ .tag = .br_table, .data = .{ .payload = table_extra_index } });
     try func.mir_extra.ensureUnusedCapacity(func.gpa, depth);
 
     var value: u32 = lowest.?;
     while (value <= highest.?) : (value += 1) {
         const idx: u32 = blk: {
             for (values.items) |val| {
                 if (val == value) break :blk 1;
             }
             break :blk 0;
         };
         func.mir_extra.appendAssumeCapacity(idx);
     }
     try func.endBlock();
 
     // 'false' branch (i.e. error set does not have value
     // ensure we set local to 0 in case the local was re-used.
     try func.addImm32(0);
     try func.addLabel(.local_set, result.local.value);
     try func.addLabel(.br, 1);
     try func.endBlock();
 
     // 'true' branch
     try func.addImm32(1);
     try func.addLabel(.local_set, result.local.value);
     try func.addLabel(.br, 0);
     try func.endBlock();
 
     return func.finishAir(inst, result, &.{ty_op.operand});
 }
 
 inline fn useAtomicFeature(func: *const CodeGen) bool {
     return std.Target.wasm.featureSetHas(func.target.cpu.features, .atomics);
 }
 
 fn airCmpxchg(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const ty_pl = func.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
     const extra = func.air.extraData(Air.Cmpxchg, ty_pl.payload).data;
 
     const ptr_ty = func.typeOf(extra.ptr);
     const ty = ptr_ty.childType(mod);
     const result_ty = func.typeOfIndex(inst);
 
     const ptr_operand = try func.resolveInst(extra.ptr);
     const expected_val = try func.resolveInst(extra.expected_value);
     const new_val = try func.resolveInst(extra.new_value);
 
     const cmp_result = try func.allocLocal(Type.bool);
 
     const ptr_val = if (func.useAtomicFeature()) val: {
         const val_local = try func.allocLocal(ty);
         try func.emitWValue(ptr_operand);
         try func.lowerToStack(expected_val);
         try func.lowerToStack(new_val);
         try func.addAtomicMemArg(switch (ty.abiSize(mod)) {
             1 => .i32_atomic_rmw8_cmpxchg_u,
             2 => .i32_atomic_rmw16_cmpxchg_u,
             4 => .i32_atomic_rmw_cmpxchg,
             8 => .i32_atomic_rmw_cmpxchg,
             else => |size| return func.fail("TODO: implement `@cmpxchg` for types with abi size '{d}'", .{size}),
         }, .{
             .offset = ptr_operand.offset(),
             .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         });
         try func.addLabel(.local_tee, val_local.local.value);
         _ = try func.cmp(.stack, expected_val, ty, .eq);
         try func.addLabel(.local_set, cmp_result.local.value);
         break :val val_local;
     } else val: {
         if (ty.abiSize(mod) > 8) {
             return func.fail("TODO: Implement `@cmpxchg` for types larger than abi size of 8 bytes", .{});
         }
         const ptr_val = try WValue.toLocal(try func.load(ptr_operand, ty, 0), func, ty);
 
         try func.lowerToStack(ptr_operand);
         try func.lowerToStack(new_val);
         try func.emitWValue(ptr_val);
         _ = try func.cmp(ptr_val, expected_val, ty, .eq);
         try func.addLabel(.local_tee, cmp_result.local.value);
         try func.addTag(.select);
         try func.store(.stack, .stack, ty, 0);
 
         break :val ptr_val;
     };
 
     const result_ptr = if (isByRef(result_ty, mod)) val: {
         try func.emitWValue(cmp_result);
         try func.addImm32(-1);
         try func.addTag(.i32_xor);
         try func.addImm32(1);
         try func.addTag(.i32_and);
         const and_result = try WValue.toLocal(.stack, func, Type.bool);
         const result_ptr = try func.allocStack(result_ty);
         try func.store(result_ptr, and_result, Type.bool, @as(u32, @intCast(ty.abiSize(mod))));
         try func.store(result_ptr, ptr_val, ty, 0);
         break :val result_ptr;
     } else val: {
         try func.addImm32(0);
         try func.emitWValue(ptr_val);
         try func.emitWValue(cmp_result);
         try func.addTag(.select);
         break :val try WValue.toLocal(.stack, func, result_ty);
     };
 
     return func.finishAir(inst, result_ptr, &.{ extra.ptr, extra.expected_value, extra.new_value });
 }
 
 fn airAtomicLoad(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const atomic_load = func.air.instructions.items(.data)[@intFromEnum(inst)].atomic_load;
     const ptr = try func.resolveInst(atomic_load.ptr);
     const ty = func.typeOfIndex(inst);
 
     if (func.useAtomicFeature()) {
         const tag: wasm.AtomicsOpcode = switch (ty.abiSize(mod)) {
             1 => .i32_atomic_load8_u,
             2 => .i32_atomic_load16_u,
             4 => .i32_atomic_load,
             8 => .i64_atomic_load,
             else => |size| return func.fail("TODO: @atomicLoad for types with abi size {d}", .{size}),
         };
         try func.emitWValue(ptr);
         try func.addAtomicMemArg(tag, .{
             .offset = ptr.offset(),
             .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         });
     } else {
         _ = try func.load(ptr, ty, 0);
     }
 
     const result = try WValue.toLocal(.stack, func, ty);
     return func.finishAir(inst, result, &.{atomic_load.ptr});
 }
 
 fn airAtomicRmw(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const pl_op = func.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
     const extra = func.air.extraData(Air.AtomicRmw, pl_op.payload).data;
 
     const ptr = try func.resolveInst(pl_op.operand);
     const operand = try func.resolveInst(extra.operand);
     const ty = func.typeOfIndex(inst);
     const op: std.builtin.AtomicRmwOp = extra.op();
 
     if (func.useAtomicFeature()) {
         switch (op) {
             .Max,
             .Min,
             .Nand,
             => {
                 const tmp = try func.load(ptr, ty, 0);
                 const value = try tmp.toLocal(func, ty);
 
                 // create a loop to cmpxchg the new value
                 try func.startBlock(.loop, wasm.block_empty);
 
                 try func.emitWValue(ptr);
                 try func.emitWValue(value);
                 if (op == .Nand) {
                     const wasm_bits = toWasmBits(@as(u16, @intCast(ty.bitSize(mod)))).?;
 
                     const and_res = try func.binOp(value, operand, ty, .@"and");
                     if (wasm_bits == 32)
                         try func.addImm32(-1)
                     else if (wasm_bits == 64)
                         try func.addImm64(@as(u64, @bitCast(@as(i64, -1))))
                     else
                         return func.fail("TODO: `@atomicRmw` with operator `Nand` for types larger than 64 bits", .{});
                     _ = try func.binOp(and_res, .stack, ty, .xor);
                 } else {
                     try func.emitWValue(value);
                     try func.emitWValue(operand);
                     _ = try func.cmp(value, operand, ty, if (op == .Max) .gt else .lt);
                     try func.addTag(.select);
                 }
                 try func.addAtomicMemArg(
                     switch (ty.abiSize(mod)) {
                         1 => .i32_atomic_rmw8_cmpxchg_u,
                         2 => .i32_atomic_rmw16_cmpxchg_u,
                         4 => .i32_atomic_rmw_cmpxchg,
                         8 => .i64_atomic_rmw_cmpxchg,
                         else => return func.fail("TODO: implement `@atomicRmw` with operation `{s}` for types larger than 64 bits", .{@tagName(op)}),
                     },
                     .{
                         .offset = ptr.offset(),
                         .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
                     },
                 );
                 const select_res = try func.allocLocal(ty);
                 try func.addLabel(.local_tee, select_res.local.value);
                 _ = try func.cmp(.stack, value, ty, .neq); // leave on stack so we can use it for br_if
 
                 try func.emitWValue(select_res);
                 try func.addLabel(.local_set, value.local.value);
 
                 try func.addLabel(.br_if, 0);
                 try func.endBlock();
                 return func.finishAir(inst, value, &.{ pl_op.operand, extra.operand });
             },
 
             // the other operations have their own instructions for Wasm.
             else => {
                 try func.emitWValue(ptr);
                 try func.emitWValue(operand);
                 const tag: wasm.AtomicsOpcode = switch (ty.abiSize(mod)) {
                     1 => switch (op) {
                         .Xchg => .i32_atomic_rmw8_xchg_u,
                         .Add => .i32_atomic_rmw8_add_u,
                         .Sub => .i32_atomic_rmw8_sub_u,
                         .And => .i32_atomic_rmw8_and_u,
                         .Or => .i32_atomic_rmw8_or_u,
                         .Xor => .i32_atomic_rmw8_xor_u,
                         else => unreachable,
                     },
                     2 => switch (op) {
                         .Xchg => .i32_atomic_rmw16_xchg_u,
                         .Add => .i32_atomic_rmw16_add_u,
                         .Sub => .i32_atomic_rmw16_sub_u,
                         .And => .i32_atomic_rmw16_and_u,
                         .Or => .i32_atomic_rmw16_or_u,
                         .Xor => .i32_atomic_rmw16_xor_u,
                         else => unreachable,
                     },
                     4 => switch (op) {
                         .Xchg => .i32_atomic_rmw_xchg,
                         .Add => .i32_atomic_rmw_add,
                         .Sub => .i32_atomic_rmw_sub,
                         .And => .i32_atomic_rmw_and,
                         .Or => .i32_atomic_rmw_or,
                         .Xor => .i32_atomic_rmw_xor,
                         else => unreachable,
                     },
                     8 => switch (op) {
                         .Xchg => .i64_atomic_rmw_xchg,
                         .Add => .i64_atomic_rmw_add,
                         .Sub => .i64_atomic_rmw_sub,
                         .And => .i64_atomic_rmw_and,
                         .Or => .i64_atomic_rmw_or,
                         .Xor => .i64_atomic_rmw_xor,
                         else => unreachable,
                     },
                     else => |size| return func.fail("TODO: Implement `@atomicRmw` for types with abi size {d}", .{size}),
                 };
                 try func.addAtomicMemArg(tag, .{
                     .offset = ptr.offset(),
                     .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
                 });
                 const result = try WValue.toLocal(.stack, func, ty);
                 return func.finishAir(inst, result, &.{ pl_op.operand, extra.operand });
             },
         }
     } else {
         const loaded = try func.load(ptr, ty, 0);
         const result = try loaded.toLocal(func, ty);
 
         switch (op) {
             .Xchg => {
                 try func.store(ptr, operand, ty, 0);
             },
             .Add,
             .Sub,
             .And,
             .Or,
             .Xor,
             => {
                 try func.emitWValue(ptr);
                 _ = try func.binOp(result, operand, ty, switch (op) {
                     .Add => .add,
                     .Sub => .sub,
                     .And => .@"and",
                     .Or => .@"or",
                     .Xor => .xor,
                     else => unreachable,
                 });
                 if (ty.isInt(mod) and (op == .Add or op == .Sub)) {
                     _ = try func.wrapOperand(.stack, ty);
                 }
                 try func.store(.stack, .stack, ty, ptr.offset());
             },
             .Max,
             .Min,
             => {
                 try func.emitWValue(ptr);
                 try func.emitWValue(result);
                 try func.emitWValue(operand);
                 _ = try func.cmp(result, operand, ty, if (op == .Max) .gt else .lt);
                 try func.addTag(.select);
                 try func.store(.stack, .stack, ty, ptr.offset());
             },
             .Nand => {
                 const wasm_bits = toWasmBits(@as(u16, @intCast(ty.bitSize(mod)))).?;
 
                 try func.emitWValue(ptr);
                 const and_res = try func.binOp(result, operand, ty, .@"and");
                 if (wasm_bits == 32)
                     try func.addImm32(-1)
                 else if (wasm_bits == 64)
                     try func.addImm64(@as(u64, @bitCast(@as(i64, -1))))
                 else
                     return func.fail("TODO: `@atomicRmw` with operator `Nand` for types larger than 64 bits", .{});
                 _ = try func.binOp(and_res, .stack, ty, .xor);
                 try func.store(.stack, .stack, ty, ptr.offset());
             },
         }
 
         return func.finishAir(inst, result, &.{ pl_op.operand, extra.operand });
     }
 }
 
 fn airFence(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     // Only when the atomic feature is enabled, and we're not building
     // for a single-threaded build, can we emit the `fence` instruction.
     // In all other cases, we emit no instructions for a fence.
     if (func.useAtomicFeature() and !func.bin_file.base.options.single_threaded) {
         try func.addAtomicTag(.atomic_fence);
     }
 
     return func.finishAir(inst, .none, &.{});
 }
 
 fn airAtomicStore(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const mod = func.bin_file.base.comp.module.?;
     const bin_op = func.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
 
     const ptr = try func.resolveInst(bin_op.lhs);
     const operand = try func.resolveInst(bin_op.rhs);
     const ptr_ty = func.typeOf(bin_op.lhs);
     const ty = ptr_ty.childType(mod);
 
     if (func.useAtomicFeature()) {
         const tag: wasm.AtomicsOpcode = switch (ty.abiSize(mod)) {
             1 => .i32_atomic_store8,
             2 => .i32_atomic_store16,
             4 => .i32_atomic_store,
             8 => .i64_atomic_store,
             else => |size| return func.fail("TODO: @atomicLoad for types with abi size {d}", .{size}),
         };
         try func.emitWValue(ptr);
         try func.lowerToStack(operand);
         try func.addAtomicMemArg(tag, .{
             .offset = ptr.offset(),
             .alignment = @intCast(ty.abiAlignment(mod).toByteUnitsOptional().?),
         });
     } else {
         try func.store(ptr, operand, ty, 0);
     }
 
     return func.finishAir(inst, .none, &.{ bin_op.lhs, bin_op.rhs });
 }
 
 fn airFrameAddress(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     if (func.initial_stack_value == .none) {
         try func.initializeStack();
     }
     try func.emitWValue(func.bottom_stack_value);
     const result = try WValue.toLocal(.stack, func, Type.usize);
     return func.finishAir(inst, result, &.{});
 }
 
 fn typeOf(func: *CodeGen, inst: Air.Inst.Ref) Type {
     const mod = func.bin_file.base.comp.module.?;
     return func.air.typeOf(inst, &mod.intern_pool);
 }
 
 fn typeOfIndex(func: *CodeGen, inst: Air.Inst.Index) Type {
     const mod = func.bin_file.base.comp.module.?;
     return func.air.typeOfIndex(inst, &mod.intern_pool);
 }