cmd/compile: only look for struct type when crawling inline body

CL 356254 fixed crawling of embeddable types during inline. However, we
are too agressive, since when we call markEmbed for every type seen
during inlining function body. That leads to false positive that for a
non-embedded type, its unexported methods are also marked inline.

Instead, we should only look at struct type that we seen during inlining
function body, and calling markEmbed for all of its embedded fields.

Fixes #49094

Change-Id: I6ef9a8bf1fc649ec6bf75e4883f6031ec8560ba1
Reviewed-on: https://go-review.googlesource.com/c/go/+/357232
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/typecheck/crawler.go

@@ -217,7 +217,13 @@ func (p *crawler) markInlBody(n *ir.Name) {
 				//
 				// We generate the wrapper for "struct{ t }".M, and inline call
 				// to "struct{ t }".M, which makes "t.M" reachable.
-				p.markEmbed(t)
+				if t.IsStruct() {
+					for _, f := range t.FieldSlice() {
+						if f.Embedded != 0 {
+							p.markEmbed(f.Type)
+						}
+					}
+				}
 			}
 		}
 

test/fixedbugs/issue49094.dir/a.go

@@ -0,0 +1,11 @@
+// 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 a
+
+type A struct{}
+
+func (a *A) f() bool {
+	return true
+}

test/fixedbugs/issue49094.dir/b.go

@@ -0,0 +1,11 @@
+// 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 b
+
+import "./a"
+
+func M(r *a.A) string {
+	return ""
+}

test/fixedbugs/issue49094.dir/p.go

@@ -0,0 +1,15 @@
+// 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 p
+
+import (
+	"./b"
+)
+
+type S struct{}
+
+func (S) M() {
+	b.M(nil)
+}

test/fixedbugs/issue49094.go

@@ -0,0 +1,7 @@
+// compiledir
+
+// 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 ignored