cmd/compile: add test for OPmodify ops clobbering flags

Code fix was in CL 122556.  This is a corresponding test case.

Fixes #26426

Change-Id: Ib8769f367aed8bead029da0a8d2ddccee1d1dccb
Reviewed-on: https://go-review.googlesource.com/124535
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/test/fixedbugs/issue26426.go b/test/fixedbugs/issue26426.go
new file mode 100644 (file)
index 0000000..4f2a452
--- /dev/null
+++ b/test/fixedbugs/issue26426.go
@@ -0,0 +1,29 @@
+//run
+
+// Copyright 2018 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
+
+//go:noinline
+func f(p *int, v int, q1, q2 *int, r *bool) {
+       x := *r
+       if x {
+               *q1 = 1
+       }
+       *p = *p + v // This must clobber flags. Otherwise we keep x in a flags register.
+       if x {
+               *q2 = 1
+       }
+}
+
+func main() {
+       var p int
+       var q1, q2 int
+       var b bool
+       f(&p, 1, &q1, &q2, &b)
+       if q1 != 0 || q2 != 0 {
+               panic("bad")
+       }
+}