stage2: rework runtime, comptime, inline function calls

* ZIR function instructions encode the index of the block that
   contains the function instruction. This allows Zig to later scan the
   block and find the parameter instructions, which is needed for
   semantically analyzing function bodies.

 * Runtime function calls insert AIR arg instructions and then inserts
   Sema inst_map entries mapping the ZIR param instructions to them.

 * comptime/inline function call inserts Sema inst_map entries mapping
   the ZIR param instructions to the AIR callsite arguments.

With this commit we are back to the tests passing.

src/Module.zig

@@ -2899,7 +2899,6 @@ pub fn semaFile(mod: *Module, file: *Scope.File) SemaError!void {
             .namespace = &struct_obj.namespace,
             .func = null,
             .owner_func = null,
-            .param_inst_list = &.{},
         };
         defer sema.deinit();
         var block_scope: Scope.Block = .{
@@ -2954,7 +2953,6 @@ fn semaDecl(mod: *Module, decl: *Decl) !bool {
         .namespace = decl.namespace,
         .func = null,
         .owner_func = null,
-        .param_inst_list = &.{},
     };
     defer sema.deinit();
 
@@ -3625,8 +3623,6 @@ pub fn analyzeFnBody(mod: *Module, decl: *Decl, func: *Fn) SemaError!Air {
     defer decl.value_arena.?.* = arena.state;
 
     const fn_ty = decl.ty;
-    const param_inst_list = try gpa.alloc(Air.Inst.Ref, fn_ty.fnParamLen());
-    defer gpa.free(param_inst_list);
 
     var sema: Sema = .{
         .mod = mod,
@@ -3637,7 +3633,6 @@ pub fn analyzeFnBody(mod: *Module, decl: *Decl, func: *Fn) SemaError!Air {
         .namespace = decl.namespace,
         .func = func,
         .owner_func = func,
-        .param_inst_list = param_inst_list,
     };
     defer sema.deinit();
 
@@ -3656,29 +3651,55 @@ pub fn analyzeFnBody(mod: *Module, decl: *Decl, func: *Fn) SemaError!Air {
     };
     defer inner_block.instructions.deinit(gpa);
 
-    // AIR requires the arg parameters to be the first N instructions.
-    try inner_block.instructions.ensureTotalCapacity(gpa, param_inst_list.len);
-    for (param_inst_list) |*param_inst, param_index| {
+    const fn_info = sema.code.getFnInfo(func.zir_body_inst);
+    const zir_tags = sema.code.instructions.items(.tag);
+
+    // Here we are performing "runtime semantic analysis" for a function body, which means
+    // we must map the parameter ZIR instructions to `arg` AIR instructions.
+    // AIR requires the `arg` parameters to be the first N instructions.
+    const params_len = @intCast(u32, fn_ty.fnParamLen());
+    try inner_block.instructions.ensureTotalCapacity(gpa, params_len);
+    try sema.air_instructions.ensureUnusedCapacity(gpa, params_len * 2); // * 2 for the `addType`
+    try sema.inst_map.ensureUnusedCapacity(gpa, params_len);
+
+    var param_index: usize = 0;
+    for (fn_info.param_body) |inst| {
+        const name = switch (zir_tags[inst]) {
+            .param, .param_comptime => blk: {
+                const inst_data = sema.code.instructions.items(.data)[inst].pl_tok;
+                const extra = sema.code.extraData(Zir.Inst.Param, inst_data.payload_index).data;
+                break :blk extra.name;
+            },
+
+            .param_anytype, .param_anytype_comptime => blk: {
+                const str_tok = sema.code.instructions.items(.data)[inst].str_tok;
+                break :blk str_tok.start;
+            },
+
+            else => continue,
+        };
         const param_type = fn_ty.fnParamType(param_index);
+        param_index += 1;
         const ty_ref = try sema.addType(param_type);
         const arg_index = @intCast(u32, sema.air_instructions.len);
         inner_block.instructions.appendAssumeCapacity(arg_index);
-        param_inst.* = Air.indexToRef(arg_index);
-        try sema.air_instructions.append(gpa, .{
+        sema.air_instructions.appendAssumeCapacity(.{
             .tag = .arg,
-            .data = .{
-                .ty_str = .{
-                    .ty = ty_ref,
-                    .str = undefined, // Set in the semantic analysis of the arg instruction.
-                },
-            },
+            .data = .{ .ty_str = .{
+                .ty = ty_ref,
+                .str = name,
+            } },
         });
+        sema.inst_map.putAssumeCapacityNoClobber(inst, Air.indexToRef(arg_index));
     }
 
     func.state = .in_progress;
     log.debug("set {s} to in_progress", .{decl.name});
 
-    try sema.analyzeFnBody(&inner_block, func.zir_body_inst);
+    _ = sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
+        error.NeededSourceLocation => unreachable,
+        else => |e| return e,
+    };
 
     // Copy the block into place and mark that as the main block.
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len +
@@ -4330,7 +4351,6 @@ pub fn analyzeStructFields(mod: *Module, struct_obj: *Struct) CompileError!void
         .namespace = &struct_obj.namespace,
         .owner_func = null,
         .func = null,
-        .param_inst_list = &.{},
     };
     defer sema.deinit();
 
@@ -4484,7 +4504,6 @@ pub fn analyzeUnionFields(mod: *Module, union_obj: *Union) CompileError!void {
         .namespace = &union_obj.namespace,
         .owner_func = null,
         .func = null,
-        .param_inst_list = &.{},
     };
     defer sema.deinit();