1 files changed, 45 insertions, 0 deletions
diff --git a/test/atomicload.go b/test/atomicload.go
new file mode 100644
index 0000000..76f1ad4
--- /dev/null
+++ b/test/atomicload.go
@@ -0,0 +1,45 @@
+// run
+
+// 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.
+
+// Check that we do loads exactly once. The SSA backend
+// once tried to do the load in f twice, once sign extended
+// and once zero extended.  This can cause problems in
+// racy code, particularly sync/mutex.
+
+package main
+
+func f(p *byte) bool {
+	x := *p
+	a := int64(int8(x))
+	b := int64(uint8(x))
+	return a == b
+}
+
+func main() {
+	var x byte
+	const N = 1000000
+	c := make(chan struct{})
+	go func() {
+		for i := 0; i < N; i++ {
+			x = 1
+		}
+		c <- struct{}{}
+	}()
+	go func() {
+		for i := 0; i < N; i++ {
+			x = 2
+		}
+		c <- struct{}{}
+	}()
+
+	for i := 0; i < N; i++ {
+		if !f(&x) {
+			panic("non-atomic load!")
+		}
+	}
+	<-c
+	<-c
+}