From 05078023963370af0faa9689373c3bd6c7d6dfe4 Mon Sep 17 00:00:00 2001
From: Ulrich Kunitz <[email protected]>
Date: Thu, 20 Aug 2015 18:56:18 +0200
Subject: [PATCH 12/63] [release-branch.go1.5] cmd/compile: fix register
 allocation for == operator

The issue 12226 has been caused by the allocation of the same register
for the equality check of two byte values. The code in cgen.go freed the
register for the second operand before the allocation of the register
for the first operand.

Fixes #12226

Change-Id: Ie4dc33a488bd48a17f8ae9b497fd63c1ae390555
Reviewed-on: https://go-review.googlesource.com/13771
Reviewed-by: Russ Cox <[email protected]>
Reviewed-on: https://go-review.googlesource.com/14227
Reviewed-by: Ian Lance Taylor <[email protected]>
---
 src/cmd/compile/internal/gc/cgen.go |  2 +-
 test/fixedbugs/issue12226.go        | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue12226.go

diff --git a/src/cmd/compile/internal/gc/cgen.go b/src/cmd/compile/internal/gc/cgen.go
index 4160ae9..b6a3e5b 100644
--- a/src/cmd/compile/internal/gc/cgen.go
+++ b/src/cmd/compile/internal/gc/cgen.go
@@ -2018,11 +2018,11 @@ func bgenx(n, res *Node, wantTrue bool, likely int, to *obj.Prog) {
 		Regalloc(&n2, nr.Type, nil)
 		Cgen(nr, &n2)
 		nr = &n2
-		Regfree(&n2)
 
 		Regalloc(&n1, nl.Type, nil)
 		Cgen(&tmp, &n1)
 		Regfree(&n1)
+		Regfree(&n2)
 	} else {
 		var n1 Node
 		if !nl.Addable && Ctxt.Arch.Thechar == '8' {
diff --git a/test/fixedbugs/issue12226.go b/test/fixedbugs/issue12226.go
new file mode 100644
index 0000000..2246711
--- /dev/null
+++ b/test/fixedbugs/issue12226.go
@@ -0,0 +1,15 @@
+// run
+
+// Copyright 2015 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
+
+import "fmt"
+
+func main() {
+	if []byte("foo")[0] == []byte("b")[0] {
+		fmt.Println("BUG: \"foo\" and \"b\" appear to have the same first byte")
+	}
+}
-- 
2.6.1