cmd/compile/internal/gc: assert size of important types

Add tests to ensure that the size of important types don't change
unexpectedly.

Skip the test on nacl platforms because of their unusual padding
requirements.

Change-Id: Iddb127a99499e089a309b721f5073356c0da8b24
Reviewed-on: https://go-review.googlesource.com/20285
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -0,0 +1,43 @@
+// Copyright 2016 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.
+
+// +build !nacl
+
+package gc
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+// Assert that the size of important structures do not change unexpectedly.
+
+func TestSizeof(t *testing.T) {
+	const _64bit = unsafe.Sizeof(uintptr(0)) == 8
+
+	var tests = []struct {
+		val    interface{} // type as a value
+		_32bit uintptr     // size on 32bit platforms
+		_64bit uintptr     // size on 64bit platforms
+	}{
+		{Flow{}, 52, 88},
+		{Func{}, 104, 184},
+		{Name{}, 52, 80},
+		{Node{}, 92, 144},
+		{Sym{}, 64, 112},
+		{Type{}, 144, 240},
+	}
+
+	for _, tt := range tests {
+		want := tt._32bit
+		if _64bit {
+			want = tt._64bit
+		}
+		got := reflect.TypeOf(tt.val).Size()
+		if want != got {
+			t.Errorf("unsafe.Sizeof(%T): want %d, got %d", tt.val, want, got)
+		}
+	}
+}