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// 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
}
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