reader.go

			// Quirkish. TODO(mdempsky): Document why.
			if name.AutoTemp() {
				name.SetEsc(ir.EscUnknown)

				if base.Flag.GenDwarfInl != 0 {
					name.SetInlLocal(true)
				} else {
					name.SetPos(r.inlCall.Pos())
				}
			}
		}
	}

	body.Append(ir.NewLabelStmt(call.Pos(), r.retlabel))

	res := ir.NewInlinedCallExpr(call.Pos(), body, append([]ir.Node(nil), r.retvars...))
	res.SetInit(init)
	res.SetType(call.Type())
	res.SetTypecheck(1)

	// Inlining shouldn't add any functions to todoBodies.
	assert(len(todoBodies) == 0)

	return res
}

// inlReturn returns a statement that can substitute for the given
// return statement when inlining.
func (r *reader) inlReturn(ret *ir.ReturnStmt) *ir.BlockStmt {
	pos := r.inlCall.Pos()

	block := ir.TakeInit(ret)

	if results := ret.Results; len(results) != 0 {
		assert(len(r.retvars) == len(results))

		as2 := ir.NewAssignListStmt(pos, ir.OAS2, append([]ir.Node(nil), r.retvars...), ret.Results)

		if r.delayResults {
			for _, name := range r.retvars {
				// TODO(mdempsky): Use inlined position of name.Pos() instead?
				name := name.(*ir.Name)
				block.Append(ir.NewDecl(pos, ir.ODCL, name))
				name.Defn = as2
			}
		}

		block.Append(as2)
	}

	block.Append(ir.NewBranchStmt(pos, ir.OGOTO, r.retlabel))
	return ir.NewBlockStmt(pos, block)
}

// expandInline reads in an extra copy of IR to populate
// fn.Inl.{Dcl,Body}.
func expandInline(fn *ir.Func, pri pkgReaderIndex) {
	// TODO(mdempsky): Remove this function. It's currently needed by
	// dwarfgen/dwarf.go:preInliningDcls, which requires fn.Inl.Dcl to
	// create abstract function DIEs. But we should be able to provide it
	// with the same information some other way.

	fndcls := len(fn.Dcl)
	topdcls := len(typecheck.Target.Decls)

	tmpfn := ir.NewFunc(fn.Pos())
	tmpfn.Nname = ir.NewNameAt(fn.Nname.Pos(), fn.Sym())
	tmpfn.ClosureVars = fn.ClosureVars

	{
		r := pri.asReader(relocBody, syncFuncBody)
		setType(tmpfn.Nname, fn.Type())

		// Don't change parameter's Sym/Nname fields.
		r.funarghack = true

		r.funcBody(tmpfn)

		ir.WithFunc(tmpfn, func() {
			deadcode.Func(tmpfn)
		})
	}

	used := usedLocals(tmpfn.Body)

	for _, name := range tmpfn.Dcl {
		if name.Class != ir.PAUTO || used.Has(name) {
			name.Curfn = fn
			fn.Inl.Dcl = append(fn.Inl.Dcl, name)
		}
	}
	fn.Inl.Body = tmpfn.Body

	// Double check that we didn't change fn.Dcl by accident.
	assert(fndcls == len(fn.Dcl))

	// typecheck.Stmts may have added function literals to
	// typecheck.Target.Decls. Remove them again so we don't risk trying
	// to compile them multiple times.
	typecheck.Target.Decls = typecheck.Target.Decls[:topdcls]
}

// usedLocals returns a set of local variables that are used within body.
func usedLocals(body []ir.Node) ir.NameSet {
	var used ir.NameSet
	ir.VisitList(body, func(n ir.Node) {
		if n, ok := n.(*ir.Name); ok && n.Op() == ir.ONAME && n.Class == ir.PAUTO {
			used.Add(n)
		}
	})
	return used
}

// @@@ Method wrappers

// needWrapperTypes lists types for which we may need to generate
// method wrappers.
var needWrapperTypes []*types.Type

// haveWrapperTypes lists types for which we know we already have
// method wrappers, because we found the type in an imported package.
var haveWrapperTypes []*types.Type

// needMethodValueWrappers lists methods for which we may need to
// generate method value wrappers.
var needMethodValueWrappers []methodValueWrapper

// haveMethodValueWrappers lists methods for which we know we already
// have method value wrappers, because we found it in an imported
// package.
var haveMethodValueWrappers []methodValueWrapper

type methodValueWrapper struct {
	rcvr   *types.Type
	method *types.Field
}

func (r *reader) needWrapper(typ *types.Type) {
	if typ.IsPtr() {
		return
	}

	// If a type was found in an imported package, then we can assume
	// that package (or one of its transitive dependencies) already
	// generated method wrappers for it.
	if r.importedDef() {
		haveWrapperTypes = append(haveWrapperTypes, typ)
	} else {
		needWrapperTypes = append(needWrapperTypes, typ)
	}
}

func (r *reader) importedDef() bool {
	// If a type was found in an imported package, then we can assume
	// that package (or one of its transitive dependencies) already
	// generated method wrappers for it.
	//
	// Exception: If we're instantiating an imported generic type or
	// function, we might be instantiating it with type arguments not
	// previously seen before.
	//
	// TODO(mdempsky): Distinguish when a generic function or type was
	// instantiated in an imported package so that we can add types to
	// haveWrapperTypes instead.
	return r.p != localPkgReader && !r.hasTypeParams()
}

func MakeWrappers(target *ir.Package) {
	// Only unified IR emits its own wrappers.
	if base.Debug.Unified == 0 {
		return
	}

	// always generate a wrapper for error.Error (#29304)
	needWrapperTypes = append(needWrapperTypes, types.ErrorType)

	seen := make(map[string]*types.Type)

	for _, typ := range haveWrapperTypes {
		wrapType(typ, target, seen, false)
	}
	haveWrapperTypes = nil

	for _, typ := range needWrapperTypes {
		wrapType(typ, target, seen, true)
	}
	needWrapperTypes = nil

	for _, wrapper := range haveMethodValueWrappers {
		wrapMethodValue(wrapper.rcvr, wrapper.method, target, false)
	}
	haveMethodValueWrappers = nil

	for _, wrapper := range needMethodValueWrappers {
		wrapMethodValue(wrapper.rcvr, wrapper.method, target, true)
	}
	needMethodValueWrappers = nil
}

func wrapType(typ *types.Type, target *ir.Package, seen map[string]*types.Type, needed bool) {
	key := typ.LinkString()
	if prev := seen[key]; prev != nil {
		if !types.Identical(typ, prev) {
			base.Fatalf("collision: types %v and %v have link string %q", typ, prev, key)
		}
		return
	}
	seen[key] = typ

	if !needed {
		// Only called to add to 'seen'.
		return
	}

	if !typ.IsInterface() {
		typecheck.CalcMethods(typ)
	}
	for _, meth := range typ.AllMethods().Slice() {
		if meth.Sym.IsBlank() || !meth.IsMethod() {
			base.FatalfAt(meth.Pos, "invalid method: %v", meth)
		}

		methodWrapper(0, typ, meth, target)

		// For non-interface types, we also want *T wrappers.
		if !typ.IsInterface() {
			methodWrapper(1, typ, meth, target)

			// For not-in-heap types, *T is a scalar, not pointer shaped,
			// so the interface wrappers use **T.
			if typ.NotInHeap() {
				methodWrapper(2, typ, meth, target)
			}
		}
	}
}

func methodWrapper(derefs int, tbase *types.Type, method *types.Field, target *ir.Package) {
	wrapper := tbase
	for i := 0; i < derefs; i++ {
		wrapper = types.NewPtr(wrapper)
	}

	sym := ir.MethodSym(wrapper, method.Sym)
	base.Assertf(!sym.Siggen(), "already generated wrapper %v", sym)
	sym.SetSiggen(true)

	wrappee := method.Type.Recv().Type
	if types.Identical(wrapper, wrappee) ||
		!types.IsMethodApplicable(wrapper, method) ||
		!reflectdata.NeedEmit(tbase) {
		return
	}

	// TODO(mdempsky): Use method.Pos instead?
	pos := base.AutogeneratedPos

	fn := newWrapperFunc(pos, sym, wrapper, method)

	var recv ir.Node = fn.Nname.Type().Recv().Nname.(*ir.Name)

	// For simple *T wrappers around T methods, panicwrap produces a
	// nicer panic message.
	if wrapper.IsPtr() && types.Identical(wrapper.Elem(), wrappee) {
		cond := ir.NewBinaryExpr(pos, ir.OEQ, recv, types.BuiltinPkg.Lookup("nil").Def.(ir.Node))
		then := []ir.Node{ir.NewCallExpr(pos, ir.OCALL, typecheck.LookupRuntime("panicwrap"), nil)}
		fn.Body.Append(ir.NewIfStmt(pos, cond, then, nil))
	}

	// typecheck will add one implicit deref, if necessary,
	// but not-in-heap types require more for their **T wrappers.
	for i := 1; i < derefs; i++ {
		recv = Implicit(ir.NewStarExpr(pos, recv))
	}

	addTailCall(pos, fn, recv, method)

	finishWrapperFunc(fn, target)
}

func wrapMethodValue(recvType *types.Type, method *types.Field, target *ir.Package, needed bool) {
	sym := ir.MethodSymSuffix(recvType, method.Sym, "-fm")
	if sym.Uniq() {
		return
	}
	sym.SetUniq(true)

	// TODO(mdempsky): Use method.Pos instead?
	pos := base.AutogeneratedPos

	fn := newWrapperFunc(pos, sym, nil, method)
	sym.Def = fn.Nname

	// Declare and initialize variable holding receiver.
	recv := ir.NewHiddenParam(pos, fn, typecheck.Lookup(".this"), recvType)

	if !needed {
		typecheck.Func(fn)
		return
	}

	addTailCall(pos, fn, recv, method)

	finishWrapperFunc(fn, target)
}

func newWrapperFunc(pos src.XPos, sym *types.Sym, wrapper *types.Type, method *types.Field) *ir.Func {
	fn := ir.NewFunc(pos)
	fn.SetDupok(true) // TODO(mdempsky): Leave unset for local, non-generic wrappers?

	name := ir.NewNameAt(pos, sym)
	ir.MarkFunc(name)
	name.Func = fn
	name.Defn = fn
	fn.Nname = name

	sig := newWrapperType(wrapper, method)
	setType(name, sig)

	// TODO(mdempsky): De-duplicate with similar logic in funcargs.
	defParams := func(class ir.Class, params *types.Type) {
		for _, param := range params.FieldSlice() {
			name := ir.NewNameAt(param.Pos, param.Sym)
			name.Class = class
			setType(name, param.Type)

			name.Curfn = fn
			fn.Dcl = append(fn.Dcl, name)

			param.Nname = name
		}
	}

	defParams(ir.PPARAM, sig.Recvs())
	defParams(ir.PPARAM, sig.Params())
	defParams(ir.PPARAMOUT, sig.Results())

	return fn
}

func finishWrapperFunc(fn *ir.Func, target *ir.Package) {
	typecheck.Func(fn)

	ir.WithFunc(fn, func() {
		typecheck.Stmts(fn.Body)
	})

	// We generate wrappers after the global inlining pass,
	// so we're responsible for applying inlining ourselves here.
	inline.InlineCalls(fn)

	target.Decls = append(target.Decls, fn)
}

// newWrapperType returns a copy of the given signature type, but with
// the receiver parameter type substituted with recvType.
// If recvType is nil, newWrapperType returns a signature
// without a receiver parameter.
func newWrapperType(recvType *types.Type, method *types.Field) *types.Type {
	clone := func(params []*types.Field) []*types.Field {
		res := make([]*types.Field, len(params))
		for i, param := range params {
			sym := param.Sym
			if sym == nil || sym.Name == "_" {
				sym = typecheck.LookupNum(".anon", i)
			}
			res[i] = types.NewField(param.Pos, sym, param.Type)
			res[i].SetIsDDD(param.IsDDD())
		}
		return res
	}

	sig := method.Type

	var recv *types.Field
	if recvType != nil {
		recv = types.NewField(sig.Recv().Pos, typecheck.Lookup(".this"), recvType)
	}
	params := clone(sig.Params().FieldSlice())
	results := clone(sig.Results().FieldSlice())

	return types.NewSignature(types.NoPkg, recv, nil, params, results)
}

func addTailCall(pos src.XPos, fn *ir.Func, recv ir.Node, method *types.Field) {
	sig := fn.Nname.Type()
	args := make([]ir.Node, sig.NumParams())
	for i, param := range sig.Params().FieldSlice() {
		args[i] = param.Nname.(*ir.Name)
	}

	// TODO(mdempsky): Support creating OTAILCALL, when possible. See reflectdata.methodWrapper.
	// Not urgent though, because tail calls are currently incompatible with regabi anyway.

	fn.SetWrapper(true) // TODO(mdempsky): Leave unset for tail calls?

	dot := ir.NewSelectorExpr(pos, ir.OXDOT, recv, method.Sym)
	call := typecheck.Call(pos, dot, args, method.Type.IsVariadic()).(*ir.CallExpr)

	if method.Type.NumResults() == 0 {
		fn.Body.Append(call)
		return
	}

	ret := ir.NewReturnStmt(pos, nil)
	ret.Results = []ir.Node{call}
	fn.Body.Append(ret)
}