cmd/compile: make -asmhdr work with type aliases

For "type T = U" we were accidentally emitting a #define for "U__size"
instead of "T__size".

Fixes #22877.

Change-Id: I5ed6757d697753ed6d944077c16150759f6e1285
Reviewed-on: https://go-review.googlesource.com/80759
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -387,10 +387,10 @@ func dumpasmhdr() {
 			if !t.IsStruct() || t.StructType().Map != nil || t.IsFuncArgStruct() {
 				break
 			}
-			fmt.Fprintf(b, "#define %s__size %d\n", t.Sym.Name, int(t.Width))
-			for _, t := range t.Fields().Slice() {
-				if !t.Sym.IsBlank() {
-					fmt.Fprintf(b, "#define %s_%s %d\n", n.Sym.Name, t.Sym.Name, int(t.Offset))
+			fmt.Fprintf(b, "#define %s__size %d\n", n.Sym.Name, int(t.Width))
+			for _, f := range t.Fields().Slice() {
+				if !f.Sym.IsBlank() {
+					fmt.Fprintf(b, "#define %s_%s %d\n", n.Sym.Name, f.Sym.Name, int(f.Offset))
 				}
 			}
 		}

test/fixedbugs/issue22877.dir/p.go

@@ -0,0 +1,14 @@
+// Copyright 2017 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
+
+type S struct{ i int }
+type SS = S
+
+func sub()
+
+func main() {
+	sub()
+}

test/fixedbugs/issue22877.dir/p.s

@@ -0,0 +1,8 @@
+// Copyright 2017 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.
+
+#include "go_asm.h"
+
+TEXT ·sub(SB), 0, $0
+	RET

test/fixedbugs/issue22877.go

@@ -0,0 +1,7 @@
+// builddir
+
+// Copyright 2017 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

test/run.go

@@ -736,6 +736,9 @@ func (t *test) run() {
 		}
 		var objs []string
 		cmd := []string{"go", "tool", "compile", "-e", "-D", ".", "-I", ".", "-o", "go.o"}
+		if len(asms) > 0 {
+			cmd = append(cmd, "-asmhdr", "go_asm.h")
+		}
 		for _, file := range gos {
 			cmd = append(cmd, filepath.Join(longdir, file.Name()))
 		}