zig

blob 1604f045 (110036B) - Raw

---

 const std = @import("std");
 const builtin = @import("builtin");
 const mem = std.mem;
 const math = std.math;
 const assert = std.debug.assert;
 const Air = @import("../../Air.zig");
 const Mir = @import("Mir.zig");
 const Emit = @import("Emit.zig");
 const Liveness = @import("../../Liveness.zig");
 const Type = @import("../../type.zig").Type;
 const Value = @import("../../value.zig").Value;
 const TypedValue = @import("../../TypedValue.zig");
 const link = @import("../../link.zig");
 const Module = @import("../../Module.zig");
 const Compilation = @import("../../Compilation.zig");
 const ErrorMsg = Module.ErrorMsg;
 const Target = std.Target;
 const Allocator = mem.Allocator;
 const trace = @import("../../tracy.zig").trace;
 const DW = std.dwarf;
 const leb128 = std.leb;
 const log = std.log.scoped(.codegen);
 const build_options = @import("build_options");
 const RegisterManagerFn = @import("../../register_manager.zig").RegisterManager;
 const RegisterManager = RegisterManagerFn(Self, Register, &callee_preserved_regs);
 
 const FnResult = @import("../../codegen.zig").FnResult;
 const GenerateSymbolError = @import("../../codegen.zig").GenerateSymbolError;
 const DebugInfoOutput = @import("../../codegen.zig").DebugInfoOutput;
 
 const bits = @import("bits.zig");
 const abi = @import("abi.zig");
 const Register = bits.Register;
 const Instruction = abi.Instruction;
 const callee_preserved_regs = abi.callee_preserved_regs;
 
 const InnerError = error{
     OutOfMemory,
     CodegenFail,
     OutOfRegisters,
 };
 
 gpa: Allocator,
 air: Air,
 liveness: Liveness,
 bin_file: *link.File,
 target: *const std.Target,
 mod_fn: *const Module.Fn,
 code: *std.ArrayList(u8),
 debug_output: DebugInfoOutput,
 err_msg: ?*ErrorMsg,
 args: []MCValue,
 ret_mcv: MCValue,
 fn_type: Type,
 arg_index: usize,
 src_loc: Module.SrcLoc,
 stack_align: u32,
 
 /// MIR Instructions
 mir_instructions: std.MultiArrayList(Mir.Inst) = .{},
 /// MIR extra data
 mir_extra: std.ArrayListUnmanaged(u32) = .{},
 
 /// Byte offset within the source file of the ending curly.
 end_di_line: u32,
 end_di_column: u32,
 
 /// The value is an offset into the `Function` `code` from the beginning.
 /// To perform the reloc, write 32-bit signed little-endian integer
 /// which is a relative jump, based on the address following the reloc.
 exitlude_jump_relocs: std.ArrayListUnmanaged(usize) = .{},
 
 /// Whenever there is a runtime branch, we push a Branch onto this stack,
 /// and pop it off when the runtime branch joins. This provides an "overlay"
 /// of the table of mappings from instructions to `MCValue` from within the branch.
 /// This way we can modify the `MCValue` for an instruction in different ways
 /// within different branches. Special consideration is needed when a branch
 /// joins with its parent, to make sure all instructions have the same MCValue
 /// across each runtime branch upon joining.
 branch_stack: *std.ArrayList(Branch),
 
 // Key is the block instruction
 blocks: std.AutoHashMapUnmanaged(Air.Inst.Index, BlockData) = .{},
 
 register_manager: RegisterManager = .{},
 /// Maps offset to what is stored there.
 stack: std.AutoHashMapUnmanaged(u32, StackAllocation) = .{},
 
 /// Offset from the stack base, representing the end of the stack frame.
 max_end_stack: u32 = 0,
 /// Represents the current end stack offset. If there is no existing slot
 /// to place a new stack allocation, it goes here, and then bumps `max_end_stack`.
 next_stack_offset: u32 = 0,
 
 /// Debug field, used to find bugs in the compiler.
 air_bookkeeping: @TypeOf(air_bookkeeping_init) = air_bookkeeping_init,
 
 const air_bookkeeping_init = if (std.debug.runtime_safety) @as(usize, 0) else {};
 
 const MCValue = union(enum) {
     /// No runtime bits. `void` types, empty structs, u0, enums with 1 tag, etc.
     /// TODO Look into deleting this tag and using `dead` instead, since every use
     /// of MCValue.none should be instead looking at the type and noticing it is 0 bits.
     none,
     /// Control flow will not allow this value to be observed.
     unreach,
     /// No more references to this value remain.
     dead,
     /// The value is undefined.
     undef,
     /// A pointer-sized integer that fits in a register.
     /// If the type is a pointer, this is the pointer address in virtual address space.
     immediate: u64,
     /// The constant was emitted into the code, at this offset.
     /// If the type is a pointer, it means the pointer address is embedded in the code.
     embedded_in_code: usize,
     /// The value is a pointer to a constant which was emitted into the code, at this offset.
     ptr_embedded_in_code: usize,
     /// The value is in a target-specific register.
     register: Register,
     /// The value is in memory at a hard-coded address.
     /// If the type is a pointer, it means the pointer address is at this memory location.
     memory: u64,
     /// The value is one of the stack variables.
     /// If the type is a pointer, it means the pointer address is in the stack at this offset.
     stack_offset: u32,
     /// The value is a pointer to one of the stack variables (payload is stack offset).
     ptr_stack_offset: u32,
 
     fn isMemory(mcv: MCValue) bool {
         return switch (mcv) {
             .embedded_in_code, .memory, .stack_offset => true,
             else => false,
         };
     }
 
     fn isImmediate(mcv: MCValue) bool {
         return switch (mcv) {
             .immediate => true,
             else => false,
         };
     }
 
     fn isMutable(mcv: MCValue) bool {
         return switch (mcv) {
             .none => unreachable,
             .unreach => unreachable,
             .dead => unreachable,
 
             .immediate,
             .embedded_in_code,
             .memory,
             .ptr_stack_offset,
             .ptr_embedded_in_code,
             .undef,
             => false,
 
             .register,
             .stack_offset,
             => true,
         };
     }
 };
 
 const Branch = struct {
     inst_table: std.AutoArrayHashMapUnmanaged(Air.Inst.Index, MCValue) = .{},
 
     fn deinit(self: *Branch, gpa: Allocator) void {
         self.inst_table.deinit(gpa);
         self.* = undefined;
     }
 };
 
 const StackAllocation = struct {
     inst: Air.Inst.Index,
     /// TODO do we need size? should be determined by inst.ty.abiSize()
     size: u32,
 };
 
 const BlockData = struct {
     relocs: std.ArrayListUnmanaged(Reloc),
     /// The first break instruction encounters `null` here and chooses a
     /// machine code value for the block result, populating this field.
     /// Following break instructions encounter that value and use it for
     /// the location to store their block results.
     mcv: MCValue,
 };
 
 const Reloc = union(enum) {
     /// The value is an offset into the `Function` `code` from the beginning.
     /// To perform the reloc, write 32-bit signed little-endian integer
     /// which is a relative jump, based on the address following the reloc.
     rel32: usize,
     /// A branch in the ARM instruction set
     arm_branch: struct {
         pos: usize,
         cond: @import("../arm/bits.zig").Condition,
     },
 };
 
 const BigTomb = struct {
     function: *Self,
     inst: Air.Inst.Index,
     tomb_bits: Liveness.Bpi,
     big_tomb_bits: u32,
     bit_index: usize,
 
     fn feed(bt: *BigTomb, op_ref: Air.Inst.Ref) void {
         const this_bit_index = bt.bit_index;
         bt.bit_index += 1;
 
         const op_int = @enumToInt(op_ref);
         if (op_int < Air.Inst.Ref.typed_value_map.len) return;
         const op_index = @intCast(Air.Inst.Index, op_int - Air.Inst.Ref.typed_value_map.len);
 
         if (this_bit_index < Liveness.bpi - 1) {
             const dies = @truncate(u1, bt.tomb_bits >> @intCast(Liveness.OperandInt, this_bit_index)) != 0;
             if (!dies) return;
         } else {
             const big_bit_index = @intCast(u5, this_bit_index - (Liveness.bpi - 1));
             const dies = @truncate(u1, bt.big_tomb_bits >> big_bit_index) != 0;
             if (!dies) return;
         }
         bt.function.processDeath(op_index);
     }
 
     fn finishAir(bt: *BigTomb, result: MCValue) void {
         const is_used = !bt.function.liveness.isUnused(bt.inst);
         if (is_used) {
             log.debug("%{d} => {}", .{ bt.inst, result });
             const branch = &bt.function.branch_stack.items[bt.function.branch_stack.items.len - 1];
             branch.inst_table.putAssumeCapacityNoClobber(bt.inst, result);
         }
         bt.function.finishAirBookkeeping();
     }
 };
 
 const Self = @This();
 
 pub fn generate(
     bin_file: *link.File,
     src_loc: Module.SrcLoc,
     module_fn: *Module.Fn,
     air: Air,
     liveness: Liveness,
     code: *std.ArrayList(u8),
     debug_output: DebugInfoOutput,
 ) GenerateSymbolError!FnResult {
     if (build_options.skip_non_native and builtin.cpu.arch != bin_file.options.target.cpu.arch) {
         @panic("Attempted to compile for architecture that was disabled by build configuration");
     }
 
     assert(module_fn.owner_decl.has_tv);
     const fn_type = module_fn.owner_decl.ty;
 
     var branch_stack = std.ArrayList(Branch).init(bin_file.allocator);
     defer {
         assert(branch_stack.items.len == 1);
         branch_stack.items[0].deinit(bin_file.allocator);
         branch_stack.deinit();
     }
     try branch_stack.append(.{});
 
     var function = Self{
         .gpa = bin_file.allocator,
         .air = air,
         .liveness = liveness,
         .target = &bin_file.options.target,
         .bin_file = bin_file,
         .mod_fn = module_fn,
         .code = code,
         .debug_output = debug_output,
         .err_msg = null,
         .args = undefined, // populated after `resolveCallingConventionValues`
         .ret_mcv = undefined, // populated after `resolveCallingConventionValues`
         .fn_type = fn_type,
         .arg_index = 0,
         .branch_stack = &branch_stack,
         .src_loc = src_loc,
         .stack_align = undefined,
         .end_di_line = module_fn.rbrace_line,
         .end_di_column = module_fn.rbrace_column,
     };
     defer function.stack.deinit(bin_file.allocator);
     defer function.blocks.deinit(bin_file.allocator);
     defer function.exitlude_jump_relocs.deinit(bin_file.allocator);
 
     var call_info = function.resolveCallingConventionValues(fn_type) catch |err| switch (err) {
         error.CodegenFail => return FnResult{ .fail = function.err_msg.? },
         error.OutOfRegisters => return FnResult{
             .fail = try ErrorMsg.create(bin_file.allocator, src_loc, "CodeGen ran out of registers. This is a bug in the Zig compiler.", .{}),
         },
         else => |e| return e,
     };
     defer call_info.deinit(&function);
 
     function.args = call_info.args;
     function.ret_mcv = call_info.return_value;
     function.stack_align = call_info.stack_align;
     function.max_end_stack = call_info.stack_byte_count;
 
     function.gen() catch |err| switch (err) {
         error.CodegenFail => return FnResult{ .fail = function.err_msg.? },
         error.OutOfRegisters => return FnResult{
             .fail = try ErrorMsg.create(bin_file.allocator, src_loc, "CodeGen ran out of registers. This is a bug in the Zig compiler.", .{}),
         },
         else => |e| return e,
     };
 
     var mir = Mir{
         .instructions = function.mir_instructions.toOwnedSlice(),
         .extra = function.mir_extra.toOwnedSlice(bin_file.allocator),
     };
     defer mir.deinit(bin_file.allocator);
 
     var emit = Emit{
         .mir = mir,
         .bin_file = bin_file,
         .debug_output = debug_output,
         .target = &bin_file.options.target,
         .src_loc = src_loc,
         .code = code,
         .prev_di_pc = 0,
         .prev_di_line = module_fn.lbrace_line,
         .prev_di_column = module_fn.lbrace_column,
     };
     defer emit.deinit();
 
     emit.emitMir() catch |err| switch (err) {
         error.EmitFail => return FnResult{ .fail = emit.err_msg.? },
         else => |e| return e,
     };
 
     if (function.err_msg) |em| {
         return FnResult{ .fail = em };
     } else {
         return FnResult{ .appended = {} };
     }
 }
 
 fn addInst(self: *Self, inst: Mir.Inst) error{OutOfMemory}!Mir.Inst.Index {
     const gpa = self.gpa;
 
     try self.mir_instructions.ensureUnusedCapacity(gpa, 1);
 
     const result_index = @intCast(Air.Inst.Index, self.mir_instructions.len);
     self.mir_instructions.appendAssumeCapacity(inst);
     return result_index;
 }
 
 pub fn addExtra(self: *Self, extra: anytype) Allocator.Error!u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     try self.mir_extra.ensureUnusedCapacity(self.gpa, fields.len);
     return self.addExtraAssumeCapacity(extra);
 }
 
 pub fn addExtraAssumeCapacity(self: *Self, extra: anytype) u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     const result = @intCast(u32, self.mir_extra.items.len);
     inline for (fields) |field| {
         self.mir_extra.appendAssumeCapacity(switch (field.field_type) {
             u32 => @field(extra, field.name),
             i32 => @bitCast(u32, @field(extra, field.name)),
             else => @compileError("bad field type"),
         });
     }
     return result;
 }
 
 fn gen(self: *Self) !void {
     const cc = self.fn_type.fnCallingConvention();
     if (cc != .Naked) {
         // TODO Finish function prologue and epilogue for riscv64.
 
         // TODO Backpatch stack offset
         // addi sp, sp, -16
         _ = try self.addInst(.{
             .tag = .addi,
             .data = .{ .i_type = .{
                 .rd = .sp,
                 .rs1 = .sp,
                 .imm12 = -16,
             } },
         });
 
         // sd ra, 8(sp)
         _ = try self.addInst(.{
             .tag = .sd,
             .data = .{ .i_type = .{
                 .rd = .ra,
                 .rs1 = .sp,
                 .imm12 = 8,
             } },
         });
 
         // sd s0, 0(sp)
         _ = try self.addInst(.{
             .tag = .sd,
             .data = .{ .i_type = .{
                 .rd = .s0,
                 .rs1 = .sp,
                 .imm12 = 0,
             } },
         });
 
         _ = try self.addInst(.{
             .tag = .dbg_prologue_end,
             .data = .{ .nop = {} },
         });
 
         try self.genBody(self.air.getMainBody());
 
         _ = try self.addInst(.{
             .tag = .dbg_epilogue_begin,
             .data = .{ .nop = {} },
         });
 
         // exitlude jumps
         if (self.exitlude_jump_relocs.items.len == 1) {
             // There is only one relocation. Hence,
             // this relocation must be at the end of
             // the code. Therefore, we can just delete
             // the space initially reserved for the
             // jump
             self.mir_instructions.len -= 1;
         } else for (self.exitlude_jump_relocs.items) |jmp_reloc| {
             _ = jmp_reloc;
             return self.fail("TODO add branches in RISCV64", .{});
         }
 
         // ld ra, 8(sp)
         _ = try self.addInst(.{
             .tag = .ld,
             .data = .{ .i_type = .{
                 .rd = .ra,
                 .rs1 = .sp,
                 .imm12 = 8,
             } },
         });
 
         // ld s0, 0(sp)
         _ = try self.addInst(.{
             .tag = .ld,
             .data = .{ .i_type = .{
                 .rd = .s0,
                 .rs1 = .sp,
                 .imm12 = 0,
             } },
         });
 
         // addi sp, sp, 16
         _ = try self.addInst(.{
             .tag = .addi,
             .data = .{ .i_type = .{
                 .rd = .sp,
                 .rs1 = .sp,
                 .imm12 = 16,
             } },
         });
 
         // ret
         _ = try self.addInst(.{
             .tag = .ret,
             .data = .{ .nop = {} },
         });
     } else {
         _ = try self.addInst(.{
             .tag = .dbg_prologue_end,
             .data = .{ .nop = {} },
         });
 
         try self.genBody(self.air.getMainBody());
 
         _ = try self.addInst(.{
             .tag = .dbg_epilogue_begin,
             .data = .{ .nop = {} },
         });
     }
 
     // Drop them off at the rbrace.
     _ = try self.addInst(.{
         .tag = .dbg_line,
         .data = .{ .dbg_line_column = .{
             .line = self.end_di_line,
             .column = self.end_di_column,
         } },
     });
 }
 
 fn genBody(self: *Self, body: []const Air.Inst.Index) InnerError!void {
     const air_tags = self.air.instructions.items(.tag);
 
     for (body) |inst| {
         const old_air_bookkeeping = self.air_bookkeeping;
         try self.ensureProcessDeathCapacity(Liveness.bpi);
 
         switch (air_tags[inst]) {
             // zig fmt: off
             .add, .ptr_add   => try self.airAdd(inst),
             .addwrap         => try self.airAddWrap(inst),
             .add_sat         => try self.airAddSat(inst),
             .sub, .ptr_sub   => try self.airSub(inst),
             .subwrap         => try self.airSubWrap(inst),
             .sub_sat         => try self.airSubSat(inst),
             .mul             => try self.airMul(inst),
             .mulwrap         => try self.airMulWrap(inst),
             .mul_sat         => try self.airMulSat(inst),
             .rem             => try self.airRem(inst),
             .mod             => try self.airMod(inst),
             .shl, .shl_exact => try self.airShl(inst),
             .shl_sat         => try self.airShlSat(inst),
             .min             => try self.airMin(inst),
             .max             => try self.airMax(inst),
             .slice           => try self.airSlice(inst),
 
             .sqrt,
             .sin,
             .cos,
             .exp,
             .exp2,
             .log,
             .log2,
             .log10,
             .fabs,
             .floor,
             .ceil,
             .round,
             .trunc_float,
             => try self.airUnaryMath(inst),
 
             .add_with_overflow => try self.airAddWithOverflow(inst),
             .sub_with_overflow => try self.airSubWithOverflow(inst),
             .mul_with_overflow => try self.airMulWithOverflow(inst),
             .shl_with_overflow => try self.airShlWithOverflow(inst),
 
             .div_float, .div_trunc, .div_floor, .div_exact => try self.airDiv(inst),
 
             .cmp_lt  => try self.airCmp(inst, .lt),
             .cmp_lte => try self.airCmp(inst, .lte),
             .cmp_eq  => try self.airCmp(inst, .eq),
             .cmp_gte => try self.airCmp(inst, .gte),
             .cmp_gt  => try self.airCmp(inst, .gt),
             .cmp_neq => try self.airCmp(inst, .neq),
 
             .bool_and        => try self.airBoolOp(inst),
             .bool_or         => try self.airBoolOp(inst),
             .bit_and         => try self.airBitAnd(inst),
             .bit_or          => try self.airBitOr(inst),
             .xor             => try self.airXor(inst),
             .shr, .shr_exact => try self.airShr(inst),
 
             .alloc           => try self.airAlloc(inst),
             .ret_ptr         => try self.airRetPtr(inst),
             .arg             => try self.airArg(inst),
             .assembly        => try self.airAsm(inst),
             .bitcast         => try self.airBitCast(inst),
             .block           => try self.airBlock(inst),
             .br              => try self.airBr(inst),
             .breakpoint      => try self.airBreakpoint(),
             .ret_addr        => try self.airRetAddr(inst),
             .frame_addr      => try self.airFrameAddress(inst),
             .fence           => try self.airFence(),
             .cond_br         => try self.airCondBr(inst),
             .dbg_stmt        => try self.airDbgStmt(inst),
             .dbg_func        => try self.airDbgFunc(inst),
             .fptrunc         => try self.airFptrunc(inst),
             .fpext           => try self.airFpext(inst),
             .intcast         => try self.airIntCast(inst),
             .trunc           => try self.airTrunc(inst),
             .bool_to_int     => try self.airBoolToInt(inst),
             .is_non_null     => try self.airIsNonNull(inst),
             .is_non_null_ptr => try self.airIsNonNullPtr(inst),
             .is_null         => try self.airIsNull(inst),
             .is_null_ptr     => try self.airIsNullPtr(inst),
             .is_non_err      => try self.airIsNonErr(inst),
             .is_non_err_ptr  => try self.airIsNonErrPtr(inst),
             .is_err          => try self.airIsErr(inst),
             .is_err_ptr      => try self.airIsErrPtr(inst),
             .load            => try self.airLoad(inst),
             .loop            => try self.airLoop(inst),
             .not             => try self.airNot(inst),
             .ptrtoint        => try self.airPtrToInt(inst),
             .ret             => try self.airRet(inst),
             .ret_load        => try self.airRetLoad(inst),
             .store           => try self.airStore(inst),
             .struct_field_ptr=> try self.airStructFieldPtr(inst),
             .struct_field_val=> try self.airStructFieldVal(inst),
             .array_to_slice  => try self.airArrayToSlice(inst),
             .int_to_float    => try self.airIntToFloat(inst),
             .float_to_int    => try self.airFloatToInt(inst),
             .cmpxchg_strong  => try self.airCmpxchg(inst),
             .cmpxchg_weak    => try self.airCmpxchg(inst),
             .atomic_rmw      => try self.airAtomicRmw(inst),
             .atomic_load     => try self.airAtomicLoad(inst),
             .memcpy          => try self.airMemcpy(inst),
             .memset          => try self.airMemset(inst),
             .set_union_tag   => try self.airSetUnionTag(inst),
             .get_union_tag   => try self.airGetUnionTag(inst),
             .clz             => try self.airClz(inst),
             .ctz             => try self.airCtz(inst),
             .popcount        => try self.airPopcount(inst),
             .byte_swap       => try self.airByteSwap(inst),
             .bit_reverse     => try self.airBitReverse(inst),
             .tag_name        => try self.airTagName(inst),
             .error_name      => try self.airErrorName(inst),
             .splat           => try self.airSplat(inst),
             .shuffle         => try self.airShuffle(inst),
             .aggregate_init  => try self.airAggregateInit(inst),
             .union_init      => try self.airUnionInit(inst),
             .prefetch        => try self.airPrefetch(inst),
             .mul_add         => try self.airMulAdd(inst),
 
             .dbg_var_ptr,
             .dbg_var_val,
             => try self.airDbgVar(inst),
 
             .call              => try self.airCall(inst, .auto),
             .call_always_tail  => try self.airCall(inst, .always_tail),
             .call_never_tail   => try self.airCall(inst, .never_tail),
             .call_never_inline => try self.airCall(inst, .never_inline),
 
             .atomic_store_unordered => try self.airAtomicStore(inst, .Unordered),
             .atomic_store_monotonic => try self.airAtomicStore(inst, .Monotonic),
             .atomic_store_release   => try self.airAtomicStore(inst, .Release),
             .atomic_store_seq_cst   => try self.airAtomicStore(inst, .SeqCst),
 
             .struct_field_ptr_index_0 => try self.airStructFieldPtrIndex(inst, 0),
             .struct_field_ptr_index_1 => try self.airStructFieldPtrIndex(inst, 1),
             .struct_field_ptr_index_2 => try self.airStructFieldPtrIndex(inst, 2),
             .struct_field_ptr_index_3 => try self.airStructFieldPtrIndex(inst, 3),
 
             .field_parent_ptr => try self.airFieldParentPtr(inst),
 
             .switch_br       => try self.airSwitch(inst),
             .slice_ptr       => try self.airSlicePtr(inst),
             .slice_len       => try self.airSliceLen(inst),
 
             .ptr_slice_len_ptr => try self.airPtrSliceLenPtr(inst),
             .ptr_slice_ptr_ptr => try self.airPtrSlicePtrPtr(inst),
 
             .array_elem_val      => try self.airArrayElemVal(inst),
             .slice_elem_val      => try self.airSliceElemVal(inst),
             .slice_elem_ptr      => try self.airSliceElemPtr(inst),
             .ptr_elem_val        => try self.airPtrElemVal(inst),
             .ptr_elem_ptr        => try self.airPtrElemPtr(inst),
 
             .constant => unreachable, // excluded from function bodies
             .const_ty => unreachable, // excluded from function bodies
             .unreach  => self.finishAirBookkeeping(),
 
             .optional_payload           => try self.airOptionalPayload(inst),
             .optional_payload_ptr       => try self.airOptionalPayloadPtr(inst),
             .optional_payload_ptr_set   => try self.airOptionalPayloadPtrSet(inst),
             .unwrap_errunion_err        => try self.airUnwrapErrErr(inst),
             .unwrap_errunion_payload    => try self.airUnwrapErrPayload(inst),
             .unwrap_errunion_err_ptr    => try self.airUnwrapErrErrPtr(inst),
             .unwrap_errunion_payload_ptr=> try self.airUnwrapErrPayloadPtr(inst),
             .errunion_payload_ptr_set   => try self.airErrUnionPayloadPtrSet(inst),
 
             .wrap_optional         => try self.airWrapOptional(inst),
             .wrap_errunion_payload => try self.airWrapErrUnionPayload(inst),
             .wrap_errunion_err     => try self.airWrapErrUnionErr(inst),
 
             .wasm_memory_size => unreachable,
             .wasm_memory_grow => unreachable,
             // zig fmt: on
         }
         if (std.debug.runtime_safety) {
             if (self.air_bookkeeping < old_air_bookkeeping + 1) {
                 std.debug.panic("in codegen.zig, handling of AIR instruction %{d} ('{}') did not do proper bookkeeping. Look for a missing call to finishAir.", .{ inst, air_tags[inst] });
             }
         }
     }
 }
 
 /// Asserts there is already capacity to insert into top branch inst_table.
 fn processDeath(self: *Self, inst: Air.Inst.Index) void {
     const air_tags = self.air.instructions.items(.tag);
     if (air_tags[inst] == .constant) return; // Constants are immortal.
     // When editing this function, note that the logic must synchronize with `reuseOperand`.
     const prev_value = self.getResolvedInstValue(inst);
     const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
     branch.inst_table.putAssumeCapacity(inst, .dead);
     switch (prev_value) {
         .register => |reg| {
             self.register_manager.freeReg(reg);
         },
         else => {}, // TODO process stack allocation death
     }
 }
 
 /// Called when there are no operands, and the instruction is always unreferenced.
 fn finishAirBookkeeping(self: *Self) void {
     if (std.debug.runtime_safety) {
         self.air_bookkeeping += 1;
     }
 }
 
 fn finishAir(self: *Self, inst: Air.Inst.Index, result: MCValue, operands: [Liveness.bpi - 1]Air.Inst.Ref) void {
     var tomb_bits = self.liveness.getTombBits(inst);
     for (operands) |op| {
         const dies = @truncate(u1, tomb_bits) != 0;
         tomb_bits >>= 1;
         if (!dies) continue;
         const op_int = @enumToInt(op);
         if (op_int < Air.Inst.Ref.typed_value_map.len) continue;
         const op_index = @intCast(Air.Inst.Index, op_int - Air.Inst.Ref.typed_value_map.len);
         self.processDeath(op_index);
     }
     const is_used = @truncate(u1, tomb_bits) == 0;
     if (is_used) {
         log.debug("%{d} => {}", .{ inst, result });
         const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
         branch.inst_table.putAssumeCapacityNoClobber(inst, result);
 
         switch (result) {
             .register => |reg| {
                 // In some cases (such as bitcast), an operand
                 // may be the same MCValue as the result. If
                 // that operand died and was a register, it
                 // was freed by processDeath. We have to
                 // "re-allocate" the register.
                 if (self.register_manager.isRegFree(reg)) {
                     self.register_manager.getRegAssumeFree(reg, inst);
                 }
             },
             else => {},
         }
     }
     self.finishAirBookkeeping();
 }
 
 fn ensureProcessDeathCapacity(self: *Self, additional_count: usize) !void {
     const table = &self.branch_stack.items[self.branch_stack.items.len - 1].inst_table;
     try table.ensureUnusedCapacity(self.gpa, additional_count);
 }
 
 /// Adds a Type to the .debug_info at the current position. The bytes will be populated later,
 /// after codegen for this symbol is done.
 fn addDbgInfoTypeReloc(self: *Self, ty: Type) !void {
     switch (self.debug_output) {
         .dwarf => |dbg_out| {
             assert(ty.hasRuntimeBits());
             const index = dbg_out.dbg_info.items.len;
             try dbg_out.dbg_info.resize(index + 4); // DW.AT.type,  DW.FORM.ref4
 
             const gop = try dbg_out.dbg_info_type_relocs.getOrPut(self.gpa, ty);
             if (!gop.found_existing) {
                 gop.value_ptr.* = .{
                     .off = undefined,
                     .relocs = .{},
                 };
             }
             try gop.value_ptr.relocs.append(self.gpa, @intCast(u32, index));
         },
         .plan9 => {},
         .none => {},
     }
 }
 
 fn allocMem(self: *Self, inst: Air.Inst.Index, abi_size: u32, abi_align: u32) !u32 {
     if (abi_align > self.stack_align)
         self.stack_align = abi_align;
     // TODO find a free slot instead of always appending
     const offset = mem.alignForwardGeneric(u32, self.next_stack_offset, abi_align);
     self.next_stack_offset = offset + abi_size;
     if (self.next_stack_offset > self.max_end_stack)
         self.max_end_stack = self.next_stack_offset;
     try self.stack.putNoClobber(self.gpa, offset, .{
         .inst = inst,
         .size = abi_size,
     });
     return offset;
 }
 
 /// Use a pointer instruction as the basis for allocating stack memory.
 fn allocMemPtr(self: *Self, inst: Air.Inst.Index) !u32 {
     const elem_ty = self.air.typeOfIndex(inst).elemType();
     const abi_size = math.cast(u32, elem_ty.abiSize(self.target.*)) catch {
         return self.fail("type '{}' too big to fit into stack frame", .{elem_ty});
     };
     // TODO swap this for inst.ty.ptrAlign
     const abi_align = elem_ty.abiAlignment(self.target.*);
     return self.allocMem(inst, abi_size, abi_align);
 }
 
 fn allocRegOrMem(self: *Self, inst: Air.Inst.Index, reg_ok: bool) !MCValue {
     const elem_ty = self.air.typeOfIndex(inst);
     const abi_size = math.cast(u32, elem_ty.abiSize(self.target.*)) catch {
         return self.fail("type '{}' too big to fit into stack frame", .{elem_ty});
     };
     const abi_align = elem_ty.abiAlignment(self.target.*);
     if (abi_align > self.stack_align)
         self.stack_align = abi_align;
 
     if (reg_ok) {
         // Make sure the type can fit in a register before we try to allocate one.
         const ptr_bits = self.target.cpu.arch.ptrBitWidth();
         const ptr_bytes: u64 = @divExact(ptr_bits, 8);
         if (abi_size <= ptr_bytes) {
             if (self.register_manager.tryAllocReg(inst)) |reg| {
                 return MCValue{ .register = reg };
             }
         }
     }
     const stack_offset = try self.allocMem(inst, abi_size, abi_align);
     return MCValue{ .stack_offset = stack_offset };
 }
 
 pub fn spillInstruction(self: *Self, reg: Register, inst: Air.Inst.Index) !void {
     const stack_mcv = try self.allocRegOrMem(inst, false);
     log.debug("spilling {d} to stack mcv {any}", .{ inst, stack_mcv });
     const reg_mcv = self.getResolvedInstValue(inst);
     assert(reg == reg_mcv.register);
     const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
     try branch.inst_table.put(self.gpa, inst, stack_mcv);
     try self.genSetStack(self.air.typeOfIndex(inst), stack_mcv.stack_offset, reg_mcv);
 }
 
 /// Copies a value to a register without tracking the register. The register is not considered
 /// allocated. A second call to `copyToTmpRegister` may return the same register.
 /// This can have a side effect of spilling instructions to the stack to free up a register.
 fn copyToTmpRegister(self: *Self, ty: Type, mcv: MCValue) !Register {
     const reg = try self.register_manager.allocReg(null);
     try self.genSetReg(ty, reg, mcv);
     return reg;
 }
 
 /// Allocates a new register and copies `mcv` into it.
 /// `reg_owner` is the instruction that gets associated with the register in the register table.
 /// This can have a side effect of spilling instructions to the stack to free up a register.
 fn copyToNewRegister(self: *Self, reg_owner: Air.Inst.Index, mcv: MCValue) !MCValue {
     const reg = try self.register_manager.allocReg(reg_owner);
     try self.genSetReg(self.air.typeOfIndex(reg_owner), reg, mcv);
     return MCValue{ .register = reg };
 }
 
 fn airAlloc(self: *Self, inst: Air.Inst.Index) !void {
     const stack_offset = try self.allocMemPtr(inst);
     return self.finishAir(inst, .{ .ptr_stack_offset = stack_offset }, .{ .none, .none, .none });
 }
 
 fn airRetPtr(self: *Self, inst: Air.Inst.Index) !void {
     const stack_offset = try self.allocMemPtr(inst);
     return self.finishAir(inst, .{ .ptr_stack_offset = stack_offset }, .{ .none, .none, .none });
 }
 
 fn airFptrunc(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFptrunc for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airFpext(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFpext for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airIntCast(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     if (self.liveness.isUnused(inst))
         return self.finishAir(inst, .dead, .{ ty_op.operand, .none, .none });
 
     const operand_ty = self.air.typeOf(ty_op.operand);
     const operand = try self.resolveInst(ty_op.operand);
     const info_a = operand_ty.intInfo(self.target.*);
     const info_b = self.air.typeOfIndex(inst).intInfo(self.target.*);
     if (info_a.signedness != info_b.signedness)
         return self.fail("TODO gen intcast sign safety in semantic analysis", .{});
 
     if (info_a.bits == info_b.bits)
         return self.finishAir(inst, operand, .{ ty_op.operand, .none, .none });
 
     return self.fail("TODO implement intCast for {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airTrunc(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     if (self.liveness.isUnused(inst))
         return self.finishAir(inst, .dead, .{ ty_op.operand, .none, .none });
 
     const operand = try self.resolveInst(ty_op.operand);
     _ = operand;
     return self.fail("TODO implement trunc for {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airBoolToInt(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const operand = try self.resolveInst(un_op);
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else operand;
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airNot(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement NOT for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airMin(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement min for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airMax(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement max for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airSlice(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const bin_op = self.air.extraData(Air.Bin, ty_pl.payload).data;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airAdd(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement add for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airAddWrap(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement addwrap for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airAddSat(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement add_sat for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airSub(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement sub for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airSubWrap(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement subwrap for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airSubSat(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement sub_sat for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airMul(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mul for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airMulWrap(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mulwrap for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airMulSat(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mul_sat for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airAddWithOverflow(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airAddWithOverflow for {}", .{self.target.cpu.arch});
 }
 
 fn airSubWithOverflow(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airSubWithOverflow for {}", .{self.target.cpu.arch});
 }
 
 fn airMulWithOverflow(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airMulWithOverflow for {}", .{self.target.cpu.arch});
 }
 
 fn airShlWithOverflow(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airShlWithOverflow for {}", .{self.target.cpu.arch});
 }
 
 fn airDiv(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement div for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airRem(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement rem for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airMod(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement mod for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airBitAnd(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement bitwise and for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airBitOr(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement bitwise or for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airXor(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement xor for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airShl(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shl for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airShlSat(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shl_sat for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airShr(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement shr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airOptionalPayload(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .optional_payload for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airOptionalPayloadPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .optional_payload_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airOptionalPayloadPtrSet(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .optional_payload_ptr_set for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airUnwrapErrErr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union error for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airUnwrapErrPayload(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union payload for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 // *(E!T) -> E
 fn airUnwrapErrErrPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union error ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 // *(E!T) -> *T
 fn airUnwrapErrPayloadPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement unwrap error union payload ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airErrUnionPayloadPtrSet(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement .errunion_payload_ptr_set for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airWrapOptional(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const optional_ty = self.air.typeOfIndex(inst);
 
         // Optional with a zero-bit payload type is just a boolean true
         if (optional_ty.abiSize(self.target.*) == 1)
             break :result MCValue{ .immediate = 1 };
 
         return self.fail("TODO implement wrap optional for {}", .{self.target.cpu.arch});
     };
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 /// T to E!T
 fn airWrapErrUnionPayload(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement wrap errunion payload for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 /// E to E!T
 fn airWrapErrUnionErr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement wrap errunion error for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airSlicePtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airSliceLen(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_len for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airPtrSliceLenPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_slice_len_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airPtrSlicePtrPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_slice_ptr_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airSliceElemVal(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = false; // TODO
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (!is_volatile and self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_elem_val for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airSliceElemPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.Bin, ty_pl.payload).data;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement slice_elem_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ extra.lhs, extra.rhs, .none });
 }
 
 fn airArrayElemVal(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement array_elem_val for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airPtrElemVal(self: *Self, inst: Air.Inst.Index) !void {
     const is_volatile = false; // TODO
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const result: MCValue = if (!is_volatile and self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_elem_val for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airPtrElemPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.Bin, ty_pl.payload).data;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement ptr_elem_ptr for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ extra.lhs, extra.rhs, .none });
 }
 
 fn airSetUnionTag(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     _ = bin_op;
     return self.fail("TODO implement airSetUnionTag for {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airGetUnionTag(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airGetUnionTag for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airClz(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airClz for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airCtz(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airCtz for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airPopcount(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airPopcount for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airByteSwap(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airByteSwap for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airBitReverse(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airBitReverse for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airUnaryMath(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst))
         .dead
     else
         return self.fail("TODO implement airUnaryMath for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn reuseOperand(self: *Self, inst: Air.Inst.Index, operand: Air.Inst.Ref, op_index: Liveness.OperandInt, mcv: MCValue) bool {
     if (!self.liveness.operandDies(inst, op_index))
         return false;
 
     switch (mcv) {
         .register => |reg| {
             // If it's in the registers table, need to associate the register with the
             // new instruction.
             if (RegisterManager.indexOfRegIntoTracked(reg)) |index| {
                 if (!self.register_manager.isRegFree(reg)) {
                     self.register_manager.registers[index] = inst;
                 }
             }
             log.debug("%{d} => {} (reused)", .{ inst, reg });
         },
         .stack_offset => |off| {
             log.debug("%{d} => stack offset {d} (reused)", .{ inst, off });
         },
         else => return false,
     }
 
     // Prevent the operand deaths processing code from deallocating it.
     self.liveness.clearOperandDeath(inst, op_index);
 
     // That makes us responsible for doing the rest of the stuff that processDeath would have done.
     const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
     branch.inst_table.putAssumeCapacity(Air.refToIndex(operand).?, .dead);
 
     return true;
 }
 
 fn load(self: *Self, dst_mcv: MCValue, ptr: MCValue, ptr_ty: Type) InnerError!void {
     const elem_ty = ptr_ty.elemType();
     switch (ptr) {
         .none => unreachable,
         .undef => unreachable,
         .unreach => unreachable,
         .dead => unreachable,
         .immediate => |imm| try self.setRegOrMem(elem_ty, dst_mcv, .{ .memory = imm }),
         .ptr_stack_offset => |off| try self.setRegOrMem(elem_ty, dst_mcv, .{ .stack_offset = off }),
         .ptr_embedded_in_code => |off| {
             try self.setRegOrMem(elem_ty, dst_mcv, .{ .embedded_in_code = off });
         },
         .embedded_in_code => {
             return self.fail("TODO implement loading from MCValue.embedded_in_code", .{});
         },
         .register => {
             return self.fail("TODO implement loading from MCValue.register", .{});
         },
         .memory,
         .stack_offset,
         => {
             const reg = try self.register_manager.allocReg(null);
             self.register_manager.freezeRegs(&.{reg});
             defer self.register_manager.unfreezeRegs(&.{reg});
 
             try self.genSetReg(ptr_ty, reg, ptr);
             try self.load(dst_mcv, .{ .register = reg }, ptr_ty);
         },
     }
 }
 
 fn airLoad(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const elem_ty = self.air.typeOfIndex(inst);
     const result: MCValue = result: {
         if (!elem_ty.hasRuntimeBits())
             break :result MCValue.none;
 
         const ptr = try self.resolveInst(ty_op.operand);
         const is_volatile = self.air.typeOf(ty_op.operand).isVolatilePtr();
         if (self.liveness.isUnused(inst) and !is_volatile)
             break :result MCValue.dead;
 
         const dst_mcv: MCValue = blk: {
             if (self.reuseOperand(inst, ty_op.operand, 0, ptr)) {
                 // The MCValue that holds the pointer can be re-used as the value.
                 break :blk ptr;
             } else {
                 break :blk try self.allocRegOrMem(inst, true);
             }
         };
         try self.load(dst_mcv, ptr, self.air.typeOf(ty_op.operand));
         break :result dst_mcv;
     };
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airStore(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const ptr = try self.resolveInst(bin_op.lhs);
     const value = try self.resolveInst(bin_op.rhs);
     const elem_ty = self.air.typeOf(bin_op.rhs);
     switch (ptr) {
         .none => unreachable,
         .undef => unreachable,
         .unreach => unreachable,
         .dead => unreachable,
         .immediate => |imm| {
             try self.setRegOrMem(elem_ty, .{ .memory = imm }, value);
         },
         .ptr_stack_offset => |off| {
             try self.genSetStack(elem_ty, off, value);
         },
         .ptr_embedded_in_code => |off| {
             try self.setRegOrMem(elem_ty, .{ .embedded_in_code = off }, value);
         },
         .embedded_in_code => {
             return self.fail("TODO implement storing to MCValue.embedded_in_code", .{});
         },
         .register => {
             return self.fail("TODO implement storing to MCValue.register", .{});
         },
         .memory => {
             return self.fail("TODO implement storing to MCValue.memory", .{});
         },
         .stack_offset => {
             return self.fail("TODO implement storing to MCValue.stack_offset", .{});
         },
     }
     return self.finishAir(inst, .dead, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airStructFieldPtr(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.StructField, ty_pl.payload).data;
     return self.structFieldPtr(extra.struct_operand, ty_pl.ty, extra.field_index);
 }
 
 fn airStructFieldPtrIndex(self: *Self, inst: Air.Inst.Index, index: u8) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     return self.structFieldPtr(ty_op.operand, ty_op.ty, index);
 }
 fn structFieldPtr(self: *Self, operand: Air.Inst.Ref, ty: Air.Inst.Ref, index: u32) !void {
     _ = self;
     _ = operand;
     _ = ty;
     _ = index;
     return self.fail("TODO implement codegen struct_field_ptr", .{});
     //return self.finishAir(inst, result, .{ extra.struct_ptr, .none, .none });
 }
 
 fn airStructFieldVal(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.StructField, ty_pl.payload).data;
     _ = extra;
     return self.fail("TODO implement codegen struct_field_val", .{});
     //return self.finishAir(inst, result, .{ extra.struct_ptr, .none, .none });
 }
 
 fn airFieldParentPtr(self: *Self, inst: Air.Inst.Index) !void {
     _ = self;
     _ = inst;
     return self.fail("TODO implement codegen airFieldParentPtr", .{});
 }
 
 fn genArgDbgInfo(self: *Self, inst: Air.Inst.Index, mcv: MCValue, arg_index: u32) !void {
     const ty = self.air.instructions.items(.data)[inst].ty;
     const name = self.mod_fn.getParamName(arg_index);
     const name_with_null = name.ptr[0 .. name.len + 1];
 
     switch (mcv) {
         .register => |reg| {
             switch (self.debug_output) {
                 .dwarf => |dbg_out| {
                     try dbg_out.dbg_info.ensureUnusedCapacity(3);
                     dbg_out.dbg_info.appendAssumeCapacity(link.File.Dwarf.abbrev_parameter);
                     dbg_out.dbg_info.appendSliceAssumeCapacity(&[2]u8{ // DW.AT.location, DW.FORM.exprloc
                         1, // ULEB128 dwarf expression length
                         reg.dwarfLocOp(),
                     });
                     try dbg_out.dbg_info.ensureUnusedCapacity(5 + name_with_null.len);
                     try self.addDbgInfoTypeReloc(ty); // DW.AT.type,  DW.FORM.ref4
                     dbg_out.dbg_info.appendSliceAssumeCapacity(name_with_null); // DW.AT.name, DW.FORM.string
                 },
                 .plan9 => {},
                 .none => {},
             }
         },
         .stack_offset => |offset| {
             _ = offset;
             switch (self.debug_output) {
                 .dwarf => {},
                 .plan9 => {},
                 .none => {},
             }
         },
         else => {},
     }
 }
 
 fn airArg(self: *Self, inst: Air.Inst.Index) !void {
     const arg_index = self.arg_index;
     self.arg_index += 1;
 
     const ty = self.air.typeOfIndex(inst);
     _ = ty;
 
     const result = self.args[arg_index];
     // TODO support stack-only arguments
     // TODO Copy registers to the stack
     const mcv = result;
     try self.genArgDbgInfo(inst, mcv, @intCast(u32, arg_index));
 
     if (self.liveness.isUnused(inst))
         return self.finishAirBookkeeping();
 
     switch (mcv) {
         .register => |reg| {
             self.register_manager.getRegAssumeFree(reg, inst);
         },
         else => {},
     }
 
     return self.finishAir(inst, mcv, .{ .none, .none, .none });
 }
 
 fn airBreakpoint(self: *Self) !void {
     _ = try self.addInst(.{
         .tag = .ebreak,
         .data = .{ .nop = {} },
     });
     return self.finishAirBookkeeping();
 }
 
 fn airRetAddr(self: *Self, inst: Air.Inst.Index) !void {
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airRetAddr for riscv64", .{});
     return self.finishAir(inst, result, .{ .none, .none, .none });
 }
 
 fn airFrameAddress(self: *Self, inst: Air.Inst.Index) !void {
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFrameAddress for riscv64", .{});
     return self.finishAir(inst, result, .{ .none, .none, .none });
 }
 
 fn airFence(self: *Self) !void {
     return self.fail("TODO implement fence() for {}", .{self.target.cpu.arch});
     //return self.finishAirBookkeeping();
 }
 
 fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallOptions.Modifier) !void {
     if (modifier == .always_tail) return self.fail("TODO implement tail calls for riscv64", .{});
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     const fn_ty = self.air.typeOf(pl_op.operand);
     const callee = pl_op.operand;
     const extra = self.air.extraData(Air.Call, pl_op.payload);
     const args = @bitCast([]const Air.Inst.Ref, self.air.extra[extra.end..][0..extra.data.args_len]);
 
     var info = try self.resolveCallingConventionValues(fn_ty);
     defer info.deinit(self);
 
     // Due to incremental compilation, how function calls are generated depends
     // on linking.
     if (self.bin_file.tag == link.File.Elf.base_tag or self.bin_file.tag == link.File.Coff.base_tag) {
         for (info.args) |mc_arg, arg_i| {
             const arg = args[arg_i];
             const arg_ty = self.air.typeOf(arg);
             const arg_mcv = try self.resolveInst(args[arg_i]);
 
             switch (mc_arg) {
                 .none => continue,
                 .undef => unreachable,
                 .immediate => unreachable,
                 .unreach => unreachable,
                 .dead => unreachable,
                 .embedded_in_code => unreachable,
                 .memory => unreachable,
                 .register => |reg| {
                     try self.register_manager.getReg(reg, null);
                     try self.genSetReg(arg_ty, reg, arg_mcv);
                 },
                 .stack_offset => {
                     return self.fail("TODO implement calling with parameters in memory", .{});
                 },
                 .ptr_stack_offset => {
                     return self.fail("TODO implement calling with MCValue.ptr_stack_offset arg", .{});
                 },
                 .ptr_embedded_in_code => {
                     return self.fail("TODO implement calling with MCValue.ptr_embedded_in_code arg", .{});
                 },
             }
         }
 
         if (self.air.value(callee)) |func_value| {
             if (func_value.castTag(.function)) |func_payload| {
                 const func = func_payload.data;
 
                 const ptr_bits = self.target.cpu.arch.ptrBitWidth();
                 const ptr_bytes: u64 = @divExact(ptr_bits, 8);
                 const got_addr = if (self.bin_file.cast(link.File.Elf)) |elf_file| blk: {
                     const got = &elf_file.program_headers.items[elf_file.phdr_got_index.?];
                     break :blk @intCast(u32, got.p_vaddr + func.owner_decl.link.elf.offset_table_index * ptr_bytes);
                 } else if (self.bin_file.cast(link.File.Coff)) |coff_file|
                     coff_file.offset_table_virtual_address + func.owner_decl.link.coff.offset_table_index * ptr_bytes
                 else
                     unreachable;
 
                 try self.genSetReg(Type.initTag(.usize), .ra, .{ .memory = got_addr });
                 _ = try self.addInst(.{
                     .tag = .jalr,
                     .data = .{ .i_type = .{
                         .rd = .ra,
                         .rs1 = .ra,
                         .imm12 = 0,
                     } },
                 });
             } else if (func_value.castTag(.extern_fn)) |_| {
                 return self.fail("TODO implement calling extern functions", .{});
             } else {
                 return self.fail("TODO implement calling bitcasted functions", .{});
             }
         } else {
             return self.fail("TODO implement calling runtime known function pointer", .{});
         }
     } else if (self.bin_file.cast(link.File.MachO)) |_| {
         unreachable; // unsupported architecture for MachO
     } else if (self.bin_file.cast(link.File.Plan9)) |_| {
         return self.fail("TODO implement call on plan9 for {}", .{self.target.cpu.arch});
     } else unreachable;
 
     const result: MCValue = result: {
         switch (info.return_value) {
             .register => |reg| {
                 if (RegisterManager.indexOfReg(&callee_preserved_regs, reg) == null) {
                     // Save function return value in a callee saved register
                     break :result try self.copyToNewRegister(inst, info.return_value);
                 }
             },
             else => {},
         }
         break :result info.return_value;
     };
 
     if (args.len <= Liveness.bpi - 2) {
         var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
         buf[0] = callee;
         std.mem.copy(Air.Inst.Ref, buf[1..], args);
         return self.finishAir(inst, result, buf);
     }
     var bt = try self.iterateBigTomb(inst, 1 + args.len);
     bt.feed(callee);
     for (args) |arg| {
         bt.feed(arg);
     }
     return bt.finishAir(result);
 }
 
 fn ret(self: *Self, mcv: MCValue) !void {
     const ret_ty = self.fn_type.fnReturnType();
     try self.setRegOrMem(ret_ty, self.ret_mcv, mcv);
     // Just add space for an instruction, patch this later
     const index = try self.addInst(.{
         .tag = .nop,
         .data = .{ .nop = {} },
     });
     try self.exitlude_jump_relocs.append(self.gpa, index);
 }
 
 fn airRet(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const operand = try self.resolveInst(un_op);
     try self.ret(operand);
     return self.finishAir(inst, .dead, .{ un_op, .none, .none });
 }
 
 fn airRetLoad(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const ptr = try self.resolveInst(un_op);
     _ = ptr;
     return self.fail("TODO implement airRetLoad for {}", .{self.target.cpu.arch});
     //return self.finishAir(inst, .dead, .{ un_op, .none, .none });
 }
 
 fn airCmp(self: *Self, inst: Air.Inst.Index, op: math.CompareOperator) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     if (self.liveness.isUnused(inst))
         return self.finishAir(inst, .dead, .{ bin_op.lhs, bin_op.rhs, .none });
     const ty = self.air.typeOf(bin_op.lhs);
     assert(ty.eql(self.air.typeOf(bin_op.rhs)));
     if (ty.zigTypeTag() == .ErrorSet)
         return self.fail("TODO implement cmp for errors", .{});
 
     const lhs = try self.resolveInst(bin_op.lhs);
     const rhs = try self.resolveInst(bin_op.rhs);
     _ = op;
     _ = lhs;
     _ = rhs;
 
     return self.fail("TODO implement cmp for {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn airDbgStmt(self: *Self, inst: Air.Inst.Index) !void {
     const dbg_stmt = self.air.instructions.items(.data)[inst].dbg_stmt;
 
     _ = try self.addInst(.{
         .tag = .dbg_line,
         .data = .{ .dbg_line_column = .{
             .line = dbg_stmt.line,
             .column = dbg_stmt.column,
         } },
     });
 
     return self.finishAirBookkeeping();
 }
 
 fn airDbgFunc(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const function = self.air.values[ty_pl.payload].castTag(.function).?.data;
     // TODO emit debug info for function change
     _ = function;
     return self.finishAir(inst, .dead, .{ .none, .none, .none });
 }
 
 fn airDbgVar(self: *Self, inst: Air.Inst.Index) !void {
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     const name = self.air.nullTerminatedString(pl_op.payload);
     const operand = pl_op.operand;
     // TODO emit debug info for this variable
     _ = name;
     return self.finishAir(inst, .dead, .{ operand, .none, .none });
 }
 
 fn airCondBr(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
 
     return self.fail("TODO implement condbr {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, .unreach, .{ pl_op.operand, .none, .none });
 }
 
 fn isNull(self: *Self, operand: MCValue) !MCValue {
     _ = operand;
     // Here you can specialize this instruction if it makes sense to, otherwise the default
     // will call isNonNull and invert the result.
     return self.fail("TODO call isNonNull and invert the result", .{});
 }
 
 fn isNonNull(self: *Self, operand: MCValue) !MCValue {
     _ = operand;
     // Here you can specialize this instruction if it makes sense to, otherwise the default
     // will call isNull and invert the result.
     return self.fail("TODO call isNull and invert the result", .{});
 }
 
 fn isErr(self: *Self, operand: MCValue) !MCValue {
     _ = operand;
     // Here you can specialize this instruction if it makes sense to, otherwise the default
     // will call isNonNull and invert the result.
     return self.fail("TODO call isNonErr and invert the result", .{});
 }
 
 fn isNonErr(self: *Self, operand: MCValue) !MCValue {
     _ = operand;
     // Here you can specialize this instruction if it makes sense to, otherwise the default
     // will call isNull and invert the result.
     return self.fail("TODO call isErr and invert the result", .{});
 }
 
 fn airIsNull(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand = try self.resolveInst(un_op);
         break :result try self.isNull(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsNullPtr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand_ptr = try self.resolveInst(un_op);
         const operand: MCValue = blk: {
             if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
                 // The MCValue that holds the pointer can be re-used as the value.
                 break :blk operand_ptr;
             } else {
                 break :blk try self.allocRegOrMem(inst, true);
             }
         };
         try self.load(operand, operand_ptr, self.air.typeOf(un_op));
         break :result try self.isNull(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsNonNull(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand = try self.resolveInst(un_op);
         break :result try self.isNonNull(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsNonNullPtr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand_ptr = try self.resolveInst(un_op);
         const operand: MCValue = blk: {
             if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
                 // The MCValue that holds the pointer can be re-used as the value.
                 break :blk operand_ptr;
             } else {
                 break :blk try self.allocRegOrMem(inst, true);
             }
         };
         try self.load(operand, operand_ptr, self.air.typeOf(un_op));
         break :result try self.isNonNull(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsErr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand = try self.resolveInst(un_op);
         break :result try self.isErr(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsErrPtr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand_ptr = try self.resolveInst(un_op);
         const operand: MCValue = blk: {
             if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
                 // The MCValue that holds the pointer can be re-used as the value.
                 break :blk operand_ptr;
             } else {
                 break :blk try self.allocRegOrMem(inst, true);
             }
         };
         try self.load(operand, operand_ptr, self.air.typeOf(un_op));
         break :result try self.isErr(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsNonErr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand = try self.resolveInst(un_op);
         break :result try self.isNonErr(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airIsNonErrPtr(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
         const operand_ptr = try self.resolveInst(un_op);
         const operand: MCValue = blk: {
             if (self.reuseOperand(inst, un_op, 0, operand_ptr)) {
                 // The MCValue that holds the pointer can be re-used as the value.
                 break :blk operand_ptr;
             } else {
                 break :blk try self.allocRegOrMem(inst, true);
             }
         };
         try self.load(operand, operand_ptr, self.air.typeOf(un_op));
         break :result try self.isNonErr(operand);
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airLoop(self: *Self, inst: Air.Inst.Index) !void {
     // A loop is a setup to be able to jump back to the beginning.
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const loop = self.air.extraData(Air.Block, ty_pl.payload);
     const body = self.air.extra[loop.end..][0..loop.data.body_len];
     const start_index = self.code.items.len;
     try self.genBody(body);
     try self.jump(start_index);
     return self.finishAirBookkeeping();
 }
 
 /// Send control flow to the `index` of `self.code`.
 fn jump(self: *Self, index: usize) !void {
     _ = index;
     return self.fail("TODO implement jump for {}", .{self.target.cpu.arch});
 }
 
 fn airBlock(self: *Self, inst: Air.Inst.Index) !void {
     try self.blocks.putNoClobber(self.gpa, inst, .{
         // A block is a setup to be able to jump to the end.
         .relocs = .{},
         // It also acts as a receptacle for break operands.
         // Here we use `MCValue.none` to represent a null value so that the first
         // break instruction will choose a MCValue for the block result and overwrite
         // this field. Following break instructions will use that MCValue to put their
         // block results.
         .mcv = MCValue{ .none = {} },
     });
     defer self.blocks.getPtr(inst).?.relocs.deinit(self.gpa);
 
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.Block, ty_pl.payload);
     const body = self.air.extra[extra.end..][0..extra.data.body_len];
     try self.genBody(body);
 
     for (self.blocks.getPtr(inst).?.relocs.items) |reloc| try self.performReloc(reloc);
 
     const result = self.blocks.getPtr(inst).?.mcv;
     return self.finishAir(inst, result, .{ .none, .none, .none });
 }
 
 fn airSwitch(self: *Self, inst: Air.Inst.Index) !void {
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     const condition = pl_op.operand;
     _ = condition;
     return self.fail("TODO airSwitch for {}", .{self.target.cpu.arch});
     // return self.finishAir(inst, .dead, .{ condition, .none, .none });
 }
 
 fn performReloc(self: *Self, reloc: Reloc) !void {
     _ = self;
     switch (reloc) {
         .rel32 => unreachable,
         .arm_branch => unreachable,
     }
 }
 
 fn airBr(self: *Self, inst: Air.Inst.Index) !void {
     const branch = self.air.instructions.items(.data)[inst].br;
     try self.br(branch.block_inst, branch.operand);
     return self.finishAir(inst, .dead, .{ branch.operand, .none, .none });
 }
 
 fn airBoolOp(self: *Self, inst: Air.Inst.Index) !void {
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const air_tags = self.air.instructions.items(.tag);
     _ = air_tags;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement boolean operations for {}", .{self.target.cpu.arch});
     return self.finishAir(inst, result, .{ bin_op.lhs, bin_op.rhs, .none });
 }
 
 fn br(self: *Self, block: Air.Inst.Index, operand: Air.Inst.Ref) !void {
     const block_data = self.blocks.getPtr(block).?;
 
     if (self.air.typeOf(operand).hasRuntimeBits()) {
         const operand_mcv = try self.resolveInst(operand);
         const block_mcv = block_data.mcv;
         if (block_mcv == .none) {
             block_data.mcv = operand_mcv;
         } else {
             try self.setRegOrMem(self.air.typeOfIndex(block), block_mcv, operand_mcv);
         }
     }
     return self.brVoid(block);
 }
 
 fn brVoid(self: *Self, block: Air.Inst.Index) !void {
     const block_data = self.blocks.getPtr(block).?;
 
     // Emit a jump with a relocation. It will be patched up after the block ends.
     try block_data.relocs.ensureUnusedCapacity(self.gpa, 1);
 
     return self.fail("TODO implement brvoid for {}", .{self.target.cpu.arch});
 }
 
 fn airAsm(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.Asm, ty_pl.payload);
     const is_volatile = @truncate(u1, extra.data.flags >> 31) != 0;
     const clobbers_len = @truncate(u31, extra.data.flags);
     var extra_i: usize = extra.end;
     const outputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.outputs_len]);
     extra_i += outputs.len;
     const inputs = @bitCast([]const Air.Inst.Ref, self.air.extra[extra_i..][0..extra.data.inputs_len]);
     extra_i += inputs.len;
 
     const dead = !is_volatile and self.liveness.isUnused(inst);
     const result: MCValue = if (dead) .dead else result: {
         if (outputs.len > 1) {
             return self.fail("TODO implement codegen for asm with more than 1 output", .{});
         }
 
         const output_constraint: ?[]const u8 = for (outputs) |output| {
             if (output != .none) {
                 return self.fail("TODO implement codegen for non-expr asm", .{});
             }
             const constraint = std.mem.sliceTo(std.mem.sliceAsBytes(self.air.extra[extra_i..]), 0);
             // This equation accounts for the fact that even if we have exactly 4 bytes
             // for the string, we still use the next u32 for the null terminator.
             extra_i += constraint.len / 4 + 1;
 
             break constraint;
         } else null;
 
         for (inputs) |input| {
             const constraint = std.mem.sliceTo(std.mem.sliceAsBytes(self.air.extra[extra_i..]), 0);
             // This equation accounts for the fact that even if we have exactly 4 bytes
             // for the string, we still use the next u32 for the null terminator.
             extra_i += constraint.len / 4 + 1;
 
             if (constraint.len < 3 or constraint[0] != '{' or constraint[constraint.len - 1] != '}') {
                 return self.fail("unrecognized asm input constraint: '{s}'", .{constraint});
             }
             const reg_name = constraint[1 .. constraint.len - 1];
             const reg = parseRegName(reg_name) orelse
                 return self.fail("unrecognized register: '{s}'", .{reg_name});
 
             const arg_mcv = try self.resolveInst(input);
             try self.register_manager.getReg(reg, null);
             try self.genSetReg(self.air.typeOf(input), reg, arg_mcv);
         }
 
         {
             var clobber_i: u32 = 0;
             while (clobber_i < clobbers_len) : (clobber_i += 1) {
                 const clobber = std.mem.sliceTo(std.mem.sliceAsBytes(self.air.extra[extra_i..]), 0);
                 // This equation accounts for the fact that even if we have exactly 4 bytes
                 // for the string, we still use the next u32 for the null terminator.
                 extra_i += clobber.len / 4 + 1;
 
                 // TODO honor these
             }
         }
 
         const asm_source = std.mem.sliceAsBytes(self.air.extra[extra_i..])[0..extra.data.source_len];
 
         if (mem.eql(u8, asm_source, "ecall")) {
             _ = try self.addInst(.{
                 .tag = .ecall,
                 .data = .{ .nop = {} },
             });
         } else {
             return self.fail("TODO implement support for more riscv64 assembly instructions", .{});
         }
 
         if (output_constraint) |output| {
             if (output.len < 4 or output[0] != '=' or output[1] != '{' or output[output.len - 1] != '}') {
                 return self.fail("unrecognized asm output constraint: '{s}'", .{output});
             }
             const reg_name = output[2 .. output.len - 1];
             const reg = parseRegName(reg_name) orelse
                 return self.fail("unrecognized register: '{s}'", .{reg_name});
             break :result MCValue{ .register = reg };
         } else {
             break :result MCValue{ .none = {} };
         }
     };
     simple: {
         var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
         var buf_index: usize = 0;
         for (outputs) |output| {
             if (output == .none) continue;
 
             if (buf_index >= buf.len) break :simple;
             buf[buf_index] = output;
             buf_index += 1;
         }
         if (buf_index + inputs.len > buf.len) break :simple;
         std.mem.copy(Air.Inst.Ref, buf[buf_index..], inputs);
         return self.finishAir(inst, result, buf);
     }
     var bt = try self.iterateBigTomb(inst, outputs.len + inputs.len);
     for (outputs) |output| {
         if (output == .none) continue;
 
         bt.feed(output);
     }
     for (inputs) |input| {
         bt.feed(input);
     }
     return bt.finishAir(result);
 }
 
 fn iterateBigTomb(self: *Self, inst: Air.Inst.Index, operand_count: usize) !BigTomb {
     try self.ensureProcessDeathCapacity(operand_count + 1);
     return BigTomb{
         .function = self,
         .inst = inst,
         .tomb_bits = self.liveness.getTombBits(inst),
         .big_tomb_bits = self.liveness.special.get(inst) orelse 0,
         .bit_index = 0,
     };
 }
 
 /// Sets the value without any modifications to register allocation metadata or stack allocation metadata.
 fn setRegOrMem(self: *Self, ty: Type, loc: MCValue, val: MCValue) !void {
     switch (loc) {
         .none => return,
         .register => |reg| return self.genSetReg(ty, reg, val),
         .stack_offset => |off| return self.genSetStack(ty, off, val),
         .memory => {
             return self.fail("TODO implement setRegOrMem for memory", .{});
         },
         else => unreachable,
     }
 }
 
 fn genSetStack(self: *Self, ty: Type, stack_offset: u32, mcv: MCValue) InnerError!void {
     _ = ty;
     _ = stack_offset;
     _ = mcv;
     return self.fail("TODO implement getSetStack for {}", .{self.target.cpu.arch});
 }
 
 fn genSetReg(self: *Self, ty: Type, reg: Register, mcv: MCValue) InnerError!void {
     switch (mcv) {
         .dead => unreachable,
         .ptr_stack_offset => unreachable,
         .ptr_embedded_in_code => unreachable,
         .unreach, .none => return, // Nothing to do.
         .undef => {
             if (!self.wantSafety())
                 return; // The already existing value will do just fine.
             // Write the debug undefined value.
             return self.genSetReg(ty, reg, .{ .immediate = 0xaaaaaaaaaaaaaaaa });
         },
         .immediate => |unsigned_x| {
             const x = @bitCast(i64, unsigned_x);
             if (math.minInt(i12) <= x and x <= math.maxInt(i12)) {
                 _ = try self.addInst(.{
                     .tag = .addi,
                     .data = .{ .i_type = .{
                         .rd = reg,
                         .rs1 = .zero,
                         .imm12 = @intCast(i12, x),
                     } },
                 });
             } else if (math.minInt(i32) <= x and x <= math.maxInt(i32)) {
                 const lo12 = @truncate(i12, x);
                 const carry: i32 = if (lo12 < 0) 1 else 0;
                 const hi20 = @truncate(i20, (x >> 12) +% carry);
 
                 // TODO: add test case for 32-bit immediate
                 _ = try self.addInst(.{
                     .tag = .lui,
                     .data = .{ .u_type = .{
                         .rd = reg,
                         .imm20 = hi20,
                     } },
                 });
                 _ = try self.addInst(.{
                     .tag = .addi,
                     .data = .{ .i_type = .{
                         .rd = reg,
                         .rs1 = reg,
                         .imm12 = lo12,
                     } },
                 });
             } else {
                 // li rd, immediate
                 // "Myriad sequences"
                 return self.fail("TODO genSetReg 33-64 bit immediates for riscv64", .{}); // glhf
             }
         },
         .memory => |addr| {
             // The value is in memory at a hard-coded address.
             // If the type is a pointer, it means the pointer address is at this memory location.
             try self.genSetReg(ty, reg, .{ .immediate = addr });
 
             _ = try self.addInst(.{
                 .tag = .ld,
                 .data = .{ .i_type = .{
                     .rd = reg,
                     .rs1 = reg,
                     .imm12 = 0,
                 } },
             });
             // LOAD imm=[i12 offset = 0], rs1 =
 
             // return self.fail("TODO implement genSetReg memory for riscv64");
         },
         else => return self.fail("TODO implement getSetReg for riscv64 {}", .{mcv}),
     }
 }
 
 fn airPtrToInt(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const result = try self.resolveInst(un_op);
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airBitCast(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result = try self.resolveInst(ty_op.operand);
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airArrayToSlice(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airArrayToSlice for {}", .{
         self.target.cpu.arch,
     });
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airIntToFloat(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airIntToFloat for {}", .{
         self.target.cpu.arch,
     });
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airFloatToInt(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airFloatToInt for {}", .{
         self.target.cpu.arch,
     });
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airCmpxchg(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.Block, ty_pl.payload);
     _ = extra;
     return self.fail("TODO implement airCmpxchg for {}", .{
         self.target.cpu.arch,
     });
     // return self.finishAir(inst, result, .{ extra.ptr, extra.expected_value, extra.new_value });
 }
 
 fn airAtomicRmw(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airCmpxchg for {}", .{self.target.cpu.arch});
 }
 
 fn airAtomicLoad(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airAtomicLoad for {}", .{self.target.cpu.arch});
 }
 
 fn airAtomicStore(self: *Self, inst: Air.Inst.Index, order: std.builtin.AtomicOrder) !void {
     _ = inst;
     _ = order;
     return self.fail("TODO implement airAtomicStore for {}", .{self.target.cpu.arch});
 }
 
 fn airMemset(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airMemset for {}", .{self.target.cpu.arch});
 }
 
 fn airMemcpy(self: *Self, inst: Air.Inst.Index) !void {
     _ = inst;
     return self.fail("TODO implement airMemcpy for {}", .{self.target.cpu.arch});
 }
 
 fn airTagName(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const operand = try self.resolveInst(un_op);
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else {
         _ = operand;
         return self.fail("TODO implement airTagName for riscv64", .{});
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airErrorName(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
     const operand = try self.resolveInst(un_op);
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else {
         _ = operand;
         return self.fail("TODO implement airErrorName for riscv64", .{});
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
 
 fn airSplat(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airSplat for riscv64", .{});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airShuffle(self: *Self, inst: Air.Inst.Index) !void {
     const ty_op = self.air.instructions.items(.data)[inst].ty_op;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else return self.fail("TODO implement airShuffle for riscv64", .{});
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
 }
 
 fn airAggregateInit(self: *Self, inst: Air.Inst.Index) !void {
     const vector_ty = self.air.typeOfIndex(inst);
     const len = vector_ty.vectorLen();
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const elements = @bitCast([]const Air.Inst.Ref, self.air.extra[ty_pl.payload..][0..len]);
     const result: MCValue = res: {
         if (self.liveness.isUnused(inst)) break :res MCValue.dead;
         return self.fail("TODO implement airAggregateInit for riscv64", .{});
     };
 
     if (elements.len <= Liveness.bpi - 1) {
         var buf = [1]Air.Inst.Ref{.none} ** (Liveness.bpi - 1);
         std.mem.copy(Air.Inst.Ref, &buf, elements);
         return self.finishAir(inst, result, buf);
     }
     var bt = try self.iterateBigTomb(inst, elements.len);
     for (elements) |elem| {
         bt.feed(elem);
     }
     return bt.finishAir(result);
 }
 
 fn airUnionInit(self: *Self, inst: Air.Inst.Index) !void {
     const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
     const extra = self.air.extraData(Air.UnionInit, ty_pl.payload).data;
     _ = extra;
     return self.fail("TODO implement airUnionInit for riscv64", .{});
     // return self.finishAir(inst, result, .{ extra.ptr, extra.expected_value, extra.new_value });
 }
 
 fn airPrefetch(self: *Self, inst: Air.Inst.Index) !void {
     const prefetch = self.air.instructions.items(.data)[inst].prefetch;
     return self.finishAir(inst, MCValue.dead, .{ prefetch.ptr, .none, .none });
 }
 
 fn airMulAdd(self: *Self, inst: Air.Inst.Index) !void {
     const pl_op = self.air.instructions.items(.data)[inst].pl_op;
     const extra = self.air.extraData(Air.Bin, pl_op.payload).data;
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else {
         return self.fail("TODO implement airMulAdd for riscv64", .{});
     };
     return self.finishAir(inst, result, .{ extra.lhs, extra.rhs, pl_op.operand });
 }
 
 fn resolveInst(self: *Self, inst: Air.Inst.Ref) InnerError!MCValue {
     // First section of indexes correspond to a set number of constant values.
     const ref_int = @enumToInt(inst);
     if (ref_int < Air.Inst.Ref.typed_value_map.len) {
         const tv = Air.Inst.Ref.typed_value_map[ref_int];
         if (!tv.ty.hasRuntimeBits()) {
             return MCValue{ .none = {} };
         }
         return self.genTypedValue(tv);
     }
 
     // If the type has no codegen bits, no need to store it.
     const inst_ty = self.air.typeOf(inst);
     if (!inst_ty.hasRuntimeBits())
         return MCValue{ .none = {} };
 
     const inst_index = @intCast(Air.Inst.Index, ref_int - Air.Inst.Ref.typed_value_map.len);
     switch (self.air.instructions.items(.tag)[inst_index]) {
         .constant => {
             // Constants have static lifetimes, so they are always memoized in the outer most table.
             const branch = &self.branch_stack.items[0];
             const gop = try branch.inst_table.getOrPut(self.gpa, inst_index);
             if (!gop.found_existing) {
                 const ty_pl = self.air.instructions.items(.data)[inst_index].ty_pl;
                 gop.value_ptr.* = try self.genTypedValue(.{
                     .ty = inst_ty,
                     .val = self.air.values[ty_pl.payload],
                 });
             }
             return gop.value_ptr.*;
         },
         .const_ty => unreachable,
         else => return self.getResolvedInstValue(inst_index),
     }
 }
 
 fn getResolvedInstValue(self: *Self, inst: Air.Inst.Index) MCValue {
     // Treat each stack item as a "layer" on top of the previous one.
     var i: usize = self.branch_stack.items.len;
     while (true) {
         i -= 1;
         if (self.branch_stack.items[i].inst_table.get(inst)) |mcv| {
             assert(mcv != .dead);
             return mcv;
         }
     }
 }
 
 /// If the MCValue is an immediate, and it does not fit within this type,
 /// we put it in a register.
 /// A potential opportunity for future optimization here would be keeping track
 /// of the fact that the instruction is available both as an immediate
 /// and as a register.
 fn limitImmediateType(self: *Self, operand: Air.Inst.Ref, comptime T: type) !MCValue {
     const mcv = try self.resolveInst(operand);
     const ti = @typeInfo(T).Int;
     switch (mcv) {
         .immediate => |imm| {
             // This immediate is unsigned.
             const U = std.meta.Int(.unsigned, ti.bits - @boolToInt(ti.signedness == .signed));
             if (imm >= math.maxInt(U)) {
                 return MCValue{ .register = try self.copyToTmpRegister(Type.initTag(.usize), mcv) };
             }
         },
         else => {},
     }
     return mcv;
 }
 
 fn lowerDeclRef(self: *Self, tv: TypedValue, decl: *Module.Decl) InnerError!MCValue {
     const ptr_bits = self.target.cpu.arch.ptrBitWidth();
     const ptr_bytes: u64 = @divExact(ptr_bits, 8);
     decl.alive = true;
     if (self.bin_file.cast(link.File.Elf)) |elf_file| {
         const got = &elf_file.program_headers.items[elf_file.phdr_got_index.?];
         const got_addr = got.p_vaddr + decl.link.elf.offset_table_index * ptr_bytes;
         return MCValue{ .memory = got_addr };
     } else if (self.bin_file.cast(link.File.MachO)) |_| {
         // TODO I'm hacking my way through here by repurposing .memory for storing
         // index to the GOT target symbol index.
         return MCValue{ .memory = decl.link.macho.local_sym_index };
     } else if (self.bin_file.cast(link.File.Coff)) |coff_file| {
         const got_addr = coff_file.offset_table_virtual_address + decl.link.coff.offset_table_index * ptr_bytes;
         return MCValue{ .memory = got_addr };
     } else if (self.bin_file.cast(link.File.Plan9)) |p9| {
         try p9.seeDecl(decl);
         const got_addr = p9.bases.data + decl.link.plan9.got_index.? * ptr_bytes;
         return MCValue{ .memory = got_addr };
     } else {
         return self.fail("TODO codegen non-ELF const Decl pointer", .{});
     }
     _ = tv;
 }
 
 fn genTypedValue(self: *Self, typed_value: TypedValue) InnerError!MCValue {
     if (typed_value.val.isUndef())
         return MCValue{ .undef = {} };
 
     if (typed_value.val.castTag(.decl_ref)) |payload| {
         return self.lowerDeclRef(typed_value, payload.data);
     }
     if (typed_value.val.castTag(.decl_ref_mut)) |payload| {
         return self.lowerDeclRef(typed_value, payload.data.decl);
     }
     const ptr_bits = self.target.cpu.arch.ptrBitWidth();
     switch (typed_value.ty.zigTypeTag()) {
         .Pointer => switch (typed_value.ty.ptrSize()) {
             .Slice => {
                 var buf: Type.SlicePtrFieldTypeBuffer = undefined;
                 const ptr_type = typed_value.ty.slicePtrFieldType(&buf);
                 const ptr_mcv = try self.genTypedValue(.{ .ty = ptr_type, .val = typed_value.val });
                 const slice_len = typed_value.val.sliceLen();
                 // Codegen can't handle some kinds of indirection. If the wrong union field is accessed here it may mean
                 // the Sema code needs to use anonymous Decls or alloca instructions to store data.
                 const ptr_imm = ptr_mcv.memory;
                 _ = slice_len;
                 _ = ptr_imm;
                 // We need more general support for const data being stored in memory to make this work.
                 return self.fail("TODO codegen for const slices", .{});
             },
             else => {
                 if (typed_value.val.tag() == .int_u64) {
                     return MCValue{ .immediate = typed_value.val.toUnsignedInt() };
                 }
                 return self.fail("TODO codegen more kinds of const pointers", .{});
             },
         },
         .Int => {
             const info = typed_value.ty.intInfo(self.target.*);
             if (info.bits > ptr_bits or info.signedness == .signed) {
                 return self.fail("TODO const int bigger than ptr and signed int", .{});
             }
             return MCValue{ .immediate = typed_value.val.toUnsignedInt() };
         },
         .Bool => {
             return MCValue{ .immediate = @boolToInt(typed_value.val.toBool()) };
         },
         .ComptimeInt => unreachable, // semantic analysis prevents this
         .ComptimeFloat => unreachable, // semantic analysis prevents this
         .Optional => {
             if (typed_value.ty.isPtrLikeOptional()) {
                 if (typed_value.val.isNull())
                     return MCValue{ .immediate = 0 };
 
                 var buf: Type.Payload.ElemType = undefined;
                 return self.genTypedValue(.{
                     .ty = typed_value.ty.optionalChild(&buf),
                     .val = typed_value.val,
                 });
             } else if (typed_value.ty.abiSize(self.target.*) == 1) {
                 return MCValue{ .immediate = @boolToInt(typed_value.val.isNull()) };
             }
             return self.fail("TODO non pointer optionals", .{});
         },
         .Enum => {
             if (typed_value.val.castTag(.enum_field_index)) |field_index| {
                 switch (typed_value.ty.tag()) {
                     .enum_simple => {
                         return MCValue{ .immediate = field_index.data };
                     },
                     .enum_full, .enum_nonexhaustive => {
                         const enum_full = typed_value.ty.cast(Type.Payload.EnumFull).?.data;
                         if (enum_full.values.count() != 0) {
                             const tag_val = enum_full.values.keys()[field_index.data];
                             return self.genTypedValue(.{ .ty = enum_full.tag_ty, .val = tag_val });
                         } else {
                             return MCValue{ .immediate = field_index.data };
                         }
                     },
                     else => unreachable,
                 }
             } else {
                 var int_tag_buffer: Type.Payload.Bits = undefined;
                 const int_tag_ty = typed_value.ty.intTagType(&int_tag_buffer);
                 return self.genTypedValue(.{ .ty = int_tag_ty, .val = typed_value.val });
             }
         },
         .ErrorSet => {
             switch (typed_value.val.tag()) {
                 .@"error" => {
                     const err_name = typed_value.val.castTag(.@"error").?.data.name;
                     const module = self.bin_file.options.module.?;
                     const global_error_set = module.global_error_set;
                     const error_index = global_error_set.get(err_name).?;
                     return MCValue{ .immediate = error_index };
                 },
                 else => {
                     // In this case we are rendering an error union which has a 0 bits payload.
                     return MCValue{ .immediate = 0 };
                 },
             }
         },
         .ErrorUnion => {
             const error_type = typed_value.ty.errorUnionSet();
             const payload_type = typed_value.ty.errorUnionPayload();
             const sub_val = typed_value.val.castTag(.eu_payload).?.data;
 
             if (!payload_type.hasRuntimeBits()) {
                 // We use the error type directly as the type.
                 return self.genTypedValue(.{ .ty = error_type, .val = sub_val });
             }
 
             return self.fail("TODO implement error union const of type '{}'", .{typed_value.ty});
         },
         else => return self.fail("TODO implement const of type '{}'", .{typed_value.ty}),
     }
 }
 
 const CallMCValues = struct {
     args: []MCValue,
     return_value: MCValue,
     stack_byte_count: u32,
     stack_align: u32,
 
     fn deinit(self: *CallMCValues, func: *Self) void {
         func.gpa.free(self.args);
         self.* = undefined;
     }
 };
 
 /// Caller must call `CallMCValues.deinit`.
 fn resolveCallingConventionValues(self: *Self, fn_ty: Type) !CallMCValues {
     const cc = fn_ty.fnCallingConvention();
     const param_types = try self.gpa.alloc(Type, fn_ty.fnParamLen());
     defer self.gpa.free(param_types);
     fn_ty.fnParamTypes(param_types);
     var result: CallMCValues = .{
         .args = try self.gpa.alloc(MCValue, param_types.len),
         // These undefined values must be populated before returning from this function.
         .return_value = undefined,
         .stack_byte_count = undefined,
         .stack_align = undefined,
     };
     errdefer self.gpa.free(result.args);
 
     const ret_ty = fn_ty.fnReturnType();
 
     switch (cc) {
         .Naked => {
             assert(result.args.len == 0);
             result.return_value = .{ .unreach = {} };
             result.stack_byte_count = 0;
             result.stack_align = 1;
             return result;
         },
         .Unspecified, .C => {
             // LP64D ABI
             //
             // TODO make this generic with other ABIs, in particular
             // with different hardware floating-point calling
             // conventions
             var next_register: usize = 0;
             var next_stack_offset: u32 = 0;
             const argument_registers = [_]Register{ .a0, .a1, .a2, .a3, .a4, .a5, .a6, .a7 };
 
             for (param_types) |ty, i| {
                 const param_size = @intCast(u32, ty.abiSize(self.target.*));
                 if (param_size <= 8) {
                     if (next_register < argument_registers.len) {
                         result.args[i] = .{ .register = argument_registers[next_register] };
                         next_register += 1;
                     } else {
                         result.args[i] = .{ .stack_offset = next_stack_offset };
                         next_register += next_stack_offset;
                     }
                 } else if (param_size <= 16) {
                     if (next_register < argument_registers.len - 1) {
                         return self.fail("TODO MCValues with 2 registers", .{});
                     } else if (next_register < argument_registers.len) {
                         return self.fail("TODO MCValues split register + stack", .{});
                     } else {
                         result.args[i] = .{ .stack_offset = next_stack_offset };
                         next_register += next_stack_offset;
                     }
                 } else {
                     result.args[i] = .{ .stack_offset = next_stack_offset };
                     next_register += next_stack_offset;
                 }
             }
 
             result.stack_byte_count = next_stack_offset;
             result.stack_align = 16;
         },
         else => return self.fail("TODO implement function parameters for {} on riscv64", .{cc}),
     }
 
     if (ret_ty.zigTypeTag() == .NoReturn) {
         result.return_value = .{ .unreach = {} };
     } else if (!ret_ty.hasRuntimeBits()) {
         result.return_value = .{ .none = {} };
     } else switch (cc) {
         .Naked => unreachable,
         .Unspecified, .C => {
             const ret_ty_size = @intCast(u32, ret_ty.abiSize(self.target.*));
             if (ret_ty_size <= 8) {
                 result.return_value = .{ .register = .a0 };
             } else if (ret_ty_size <= 16) {
                 return self.fail("TODO support MCValue 2 registers", .{});
             } else {
                 return self.fail("TODO support return by reference", .{});
             }
         },
         else => return self.fail("TODO implement function return values for {}", .{cc}),
     }
     return result;
 }
 
 /// TODO support scope overrides. Also note this logic is duplicated with `Module.wantSafety`.
 fn wantSafety(self: *Self) bool {
     return switch (self.bin_file.options.optimize_mode) {
         .Debug => true,
         .ReleaseSafe => true,
         .ReleaseFast => false,
         .ReleaseSmall => false,
     };
 }
 
 fn fail(self: *Self, comptime format: []const u8, args: anytype) InnerError {
     @setCold(true);
     assert(self.err_msg == null);
     self.err_msg = try ErrorMsg.create(self.bin_file.allocator, self.src_loc, format, args);
     return error.CodegenFail;
 }
 
 fn failSymbol(self: *Self, comptime format: []const u8, args: anytype) InnerError {
     @setCold(true);
     assert(self.err_msg == null);
     self.err_msg = try ErrorMsg.create(self.bin_file.allocator, self.src_loc, format, args);
     return error.CodegenFail;
 }
 
 fn parseRegName(name: []const u8) ?Register {
     if (@hasDecl(Register, "parseRegName")) {
         return Register.parseRegName(name);
     }
     return std.meta.stringToEnum(Register, name);
 }