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46 lines
798 B
46 lines
798 B
4 months ago
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// run
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// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Check that we do loads exactly once. The SSA backend
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// once tried to do the load in f twice, once sign extended
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// and once zero extended. This can cause problems in
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// racy code, particularly sync/mutex.
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package main
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func f(p *byte) bool {
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x := *p
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a := int64(int8(x))
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b := int64(uint8(x))
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return a == b
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}
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func main() {
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var x byte
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const N = 1000000
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c := make(chan struct{})
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go func() {
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for i := 0; i < N; i++ {
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x = 1
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}
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c <- struct{}{}
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}()
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go func() {
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for i := 0; i < N; i++ {
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x = 2
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}
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c <- struct{}{}
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}()
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for i := 0; i < N; i++ {
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if !f(&x) {
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panic("non-atomic load!")
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}
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}
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<-c
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<-c
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}
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