[dev.typeparams] cmd/compile: generate wrappers within unified IR

This CL extends unified IR to handle creating wrapper methods. There's
relatively little about this code that's actually specific to unified
IR, but rewriting this logic allows a few benefits:

1. It decouples unified IR from reflectdata.methodWrapper, so the
latter code can evolve freely for -G=3's needs. This will also allow
the new code to evolve to unified IR's wrapper needs, which I
anticipate will operate slightly differently.

2. It provided an opportunity to revisit a lot of the code and
simplify/update it to current style. E.g., in the process, I
discovered #46903, which unified IR now gets correctly. (I have not
yet attempted to fix reflectdata.methodWrapper.)

3. It gives a convenient way for unified IR to ensure all of the
wrapper methods it needs are generated correctly.

For now, the wrapper generation is specific to non-quirks mode.

Change-Id: I5798de6b141f29e8eb6a5c563e7049627ff2868a
Reviewed-on: https://go-review.googlesource.com/c/go/+/330569
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

6 files changed, 234 insertions, 9 deletions

diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index c0346c0206..c94f19fd47 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -186,6 +186,7 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 	base.AutogeneratedPos = makePos(src.NewFileBase("<autogenerated>", "<autogenerated>"), 1, 0)
 
 	typecheck.InitUniverse()
+	typecheck.InitRuntime()
 
 	// Parse and typecheck input.
 	noder.LoadPackage(flag.Args())
@@ -194,7 +195,6 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 
 	// Prepare for backend processing. This must happen before pkginit,
 	// because it generates itabs for initializing global variables.
-	typecheck.InitRuntime()
 	ssagen.InitConfig()
 
 	// Build init task.
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index d2fe575ffd..3a496816cc 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -16,6 +16,7 @@ import (
 	"cmd/compile/internal/deadcode"
 	"cmd/compile/internal/dwarfgen"
 	"cmd/compile/internal/ir"
+	"cmd/compile/internal/reflectdata"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
@@ -419,7 +420,7 @@ func (r *reader) interfaceType() *types.Type {
 	if len(fields) == 0 {
 		return types.Types[types.TINTER] // empty interface
 	}
-	return types.NewInterface(tpkg, fields)
+	return r.needWrapper(types.NewInterface(tpkg, fields))
 }
 
 func (r *reader) structType() *types.Type {
@@ -440,7 +441,7 @@ func (r *reader) structType() *types.Type {
 		}
 		fields[i] = f
 	}
-	return types.NewStruct(tpkg, fields)
+	return r.needWrapper(types.NewStruct(tpkg, fields))
 }
 
 func (r *reader) signature(tpkg *types.Pkg, recv *types.Field) *types.Type {
@@ -597,6 +598,10 @@ func (pr *pkgReader) objIdx(idx int, implicits, explicits []*types.Type) ir.Node
 			typ.Methods().Set(methods)
 		}
 
+		if !typ.IsPtr() {
+			r.needWrapper(typ)
+		}
+
 		return name
 
 	case objVar:
@@ -2015,3 +2020,184 @@ func usedLocals(body []ir.Node) ir.NameSet {
 	})
 	return used
 }
+
+// @@@ Method wrappers
+
+// needWrapperTypes lists types for which we may need to generate
+// method wrappers.
+var needWrapperTypes []*types.Type
+
+func (r *reader) needWrapper(typ *types.Type) *types.Type {
+	// TODO(mdempsky): Be more judicious about generating wrappers.
+	// For now, generating all possible wrappers is simple and correct,
+	// but potentially wastes a lot of time/space.
+
+	if typ.IsPtr() {
+		base.Fatalf("bad pointer type: %v", typ)
+	}
+
+	needWrapperTypes = append(needWrapperTypes, typ)
+	return typ
+}
+
+func (r *reader) wrapTypes(target *ir.Package) {
+	// always generate a wrapper for error.Error (#29304)
+	r.needWrapper(types.ErrorType)
+
+	seen := make(map[string]*types.Type)
+	for _, typ := range needWrapperTypes {
+		if typ.Sym() == nil {
+			key := typ.ShortString()
+			if prev := seen[key]; prev != nil {
+				if !types.Identical(typ, prev) {
+					base.Fatalf("collision: types %v and %v have short string %q", typ, prev, key)
+				}
+				continue
+			}
+			seen[key] = typ
+		}
+
+		r.wrapType(typ, target)
+	}
+
+	needWrapperTypes = nil
+}
+
+func (r *reader) wrapType(typ *types.Type, target *ir.Package) {
+	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)
+		}
+
+		r.methodWrapper(0, typ, meth, target)
+
+		// For non-interface types, we also want *T wrappers.
+		if !typ.IsInterface() {
+			r.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() {
+				r.methodWrapper(2, typ, meth, target)
+			}
+		}
+	}
+}
+
+func (r *reader) 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)
+	assert(!sym.Siggen())
+	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 := ir.NewFunc(pos)
+	fn.SetDupok(true)   // TODO(mdempsky): Leave unset for local, non-generic wrappers?
+	fn.SetWrapper(true) // TODO(mdempsky): Leave unset for tail calls?
+
+	fn.Nname = ir.NewNameAt(pos, sym)
+	ir.MarkFunc(fn.Nname)
+	fn.Nname.Func = fn
+	fn.Nname.Defn = fn
+
+	sig := newWrapperType(wrapper, method.Type)
+	r.setType(fn.Nname, sig)
+
+	// TODO(mdempsky): De-duplicate with similar logic in funcargs.
+	defParams := func(class ir.Class, params ...*types.Field) {
+		for _, param := range params {
+			name := ir.NewNameAt(param.Pos, param.Sym)
+			name.Class = class
+			r.setType(name, param.Type)
+
+			name.Curfn = fn
+			fn.Dcl = append(fn.Dcl, name)
+
+			param.Nname = name
+		}
+	}
+
+	defParams(ir.PPARAM, sig.Recv())
+	defParams(ir.PPARAM, sig.Params().FieldSlice()...)
+	defParams(ir.PPARAMOUT, sig.Results().FieldSlice()...)
+
+	var recv ir.Node = sig.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))
+	}
+
+	// Add implicit derefs, as necessary. typecheck will add one deref,
+	// but not-in-heap types will need another for their **T wrappers.
+	for i := 0; i < derefs; i++ {
+		recv = Implicit(ir.NewStarExpr(pos, recv))
+	}
+
+	args := make([]ir.Node, sig.NumParams())
+	for i, param := range sig.Params().FieldSlice() {
+		args[i] = param.Nname.(*ir.Name)
+	}
+
+	fn.Body.Append(newTailCall(pos, method, recv, args))
+
+	target.Decls = append(target.Decls, fn)
+}
+
+// newWrapperType returns a copy of the given signature type, but with
+// the receiver parameter type substituted with wrapper.
+func newWrapperType(wrapper, sig *types.Type) *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
+	}
+
+	recv := types.NewField(sig.Recv().Pos, typecheck.Lookup(".this"), wrapper)
+	params := clone(sig.Params().FieldSlice())
+	results := clone(sig.Results().FieldSlice())
+
+	return types.NewSignature(types.NoPkg, recv, nil, params, results)
+}
+
+func newTailCall(pos src.XPos, method *types.Field, recv ir.Node, args []ir.Node) ir.Node {
+	// TODO(mdempsky): Support creating OTAILCALL, when possible. See reflectdata.methodWrapper.
+	// Not urgent though, because tail calls are currently incompatible with regabi anyway.
+
+	call := ir.NewCallExpr(pos, ir.OCALL, ir.NewSelectorExpr(pos, ir.OXDOT, recv, method.Sym), args)
+	call.IsDDD = method.Type.IsVariadic()
+
+	if method.Type.NumResults() == 0 {
+		return call
+	}
+
+	ret := ir.NewReturnStmt(pos, nil)
+	ret.Results = []ir.Node{call}
+	return ret
+}
diff --git a/src/cmd/compile/internal/noder/unified.go b/src/cmd/compile/internal/noder/unified.go
index 7a1bb88537..292fd13c67 100644
--- a/src/cmd/compile/internal/noder/unified.go
+++ b/src/cmd/compile/internal/noder/unified.go
@@ -74,6 +74,8 @@ func unified(noders []*noder) {
 
 	if !quirksMode() {
 		writeNewExportFunc = writeNewExport
+	} else if base.Flag.G != 0 {
+		base.Errorf("cannot use -G and -d=quirksmode together")
 	}
 
 	newReadImportFunc = func(data string, pkg1 *types.Pkg, check *types2.Checker, packages map[string]*types2.Package) (pkg2 *types2.Package, err error) {
@@ -126,6 +128,11 @@ func unified(noders []*noder) {
 	}
 	todoBodies = nil
 
+	if !quirksMode() {
+		// TODO(mdempsky): Investigate generating wrappers in quirks mode too.
+		r.wrapTypes(target)
+	}
+
 	// Don't use range--typecheck can add closures to Target.Decls.
 	for i := 0; i < len(target.Decls); i++ {
 		target.Decls[i] = typecheck.Stmt(target.Decls[i])
diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index ba4bbc7631..8421e36b3d 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -1760,10 +1760,6 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 		// TODO: check that we do the right thing when method is an interface method.
 		generic = true
 	}
-	if base.Debug.Unified != 0 {
-		// TODO(mdempsky): Support dictionaries for unified IR.
-		generic = false
-	}
 	newnam := ir.MethodSym(rcvr, method.Sym)
 	lsym := newnam.Linksym()
 	if newnam.Siggen() {
@@ -1771,6 +1767,12 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 	}
 	newnam.SetSiggen(true)
 
+	// Except in quirks mode, unified IR creates its own wrappers.
+	// Complain loudly if it missed any.
+	if base.Debug.Unified != 0 && base.Debug.UnifiedQuirks == 0 {
+		base.FatalfAt(method.Pos, "missing wrapper for %+v (%+v, %v) / %+v / %+v", rcvr, orig, types.IsDirectIface(orig), method.Sym, newnam)
+	}
+
 	if !generic && types.Identical(rcvr, method.Type.Recv().Type) {
 		return lsym
 	}
diff --git a/test/fixedbugs/issue46903.go b/test/fixedbugs/issue46903.go
new file mode 100644
index 0000000000..3237a583d5
--- /dev/null
+++ b/test/fixedbugs/issue46903.go
@@ -0,0 +1,32 @@
+// run
+//go:build goexperiment.unified
+// +build goexperiment.unified
+
+// TODO(mdempsky): Enable test unconditionally. This test should pass
+// for non-unified mode too.
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+//go:notinheap
+type A struct{ B }
+type B struct{ x byte }
+type I interface{ M() *B }
+
+func (p *B) M() *B { return p }
+
+var (
+	a A
+	i I = &a
+)
+
+func main() {
+	got, want := i.M(), &a.B
+	if got != want {
+		println(got, "!=", want)
+		panic("FAIL")
+	}
+}
diff --git a/test/typeparam/issue44688.go b/test/typeparam/issue44688.go
index d70f94f706..de1140b67c 100644
--- a/test/typeparam/issue44688.go
+++ b/test/typeparam/issue44688.go
@@ -1,6 +1,4 @@
 // run -gcflags=-G=3
-//go:build goexperiment.unified
-// +build !goexperiment.unified
 
 // Copyright 2021 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style