cmd/gc: fix comparison order of parameters in mpcmpfltc(a, b)

It should compare a - b to 0, not b - a to 0.
Fixes issue 6964.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/39020044

1 files changed, 11 insertions, 0 deletions

diff --git a/test/fixedbugs/issue6964.go b/test/fixedbugs/issue6964.go
new file mode 100644
index 000000000..821735c08
--- /dev/null
+++ b/test/fixedbugs/issue6964.go
@@ -0,0 +1,11 @@
+// errorcheck
+
+// Copyright 2013 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
+
+func main() {
+	_ = string(-4 + 2i + 2) // ERROR "-4\+2i"
+}