[release-branch.go1.15] cmd/compile: export notinheap annotation to object file

In the rare case when a cgo type makes it into an object file, we need
the go:notinheap annotation to go with it.

Fixes #41432.

Change-Id: Ie2ef241ee49661792e0d8c8c46c51b2fe5c6fa7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/259300
Trust: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

misc/cgo/test/testdata/issue41761.go

@@ -0,0 +1,20 @@
+// Copyright 2020 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 cgotest
+
+/*
+   typedef struct S S;
+*/
+import "C"
+
+import (
+	"cgotest/issue41761a"
+	"testing"
+)
+
+func test41761(t *testing.T) {
+	var x issue41761a.T
+	_ = (*C.struct_S)(x.X)
+}

misc/cgo/test/testdata/issue41761a/a.go

@@ -0,0 +1,14 @@
+// Copyright 2020 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 issue41761a
+
+/*
+   typedef struct S S;
+*/
+import "C"
+
+type T struct {
+	X *C.S
+}

src/cmd/compile/internal/gc/iexport.go

@@ -492,6 +492,7 @@ func (p *iexporter) doDecl(n *Node) {
 			w.signature(m.Type)
 		}
 
+		w.typeExt(t)
 		for _, m := range ms.Slice() {
 			w.methExt(m)
 		}
@@ -1012,6 +1013,11 @@ func (w *exportWriter) symIdx(s *types.Sym) {
 	}
 }
 
+func (w *exportWriter) typeExt(t *types.Type) {
+	// Export whether this type is marked notinheap.
+	w.bool(t.NotInHeap())
+}
+
 // Inline bodies.
 
 func (w *exportWriter) stmtList(list Nodes) {

src/cmd/compile/internal/gc/iimport.go

@@ -346,6 +346,7 @@ func (r *importReader) doDecl(n *Node) {
 		}
 		t.Methods().Set(ms)
 
+		r.typeExt(t)
 		for _, m := range ms {
 			r.methExt(m)
 		}
@@ -710,6 +711,10 @@ func (r *importReader) symIdx(s *types.Sym) {
 	}
 }
 
+func (r *importReader) typeExt(t *types.Type) {
+	t.SetNotInHeap(r.bool())
+}
+
 func (r *importReader) doInline(n *Node) {
 	if len(n.Func.Inl.Body) != 0 {
 		Fatalf("%v already has inline body", n)