Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1 | // run |
| 2 | |
| 3 | // Copyright 2016 The Go Authors. All rights reserved. |
| 4 | // Use of this source code is governed by a BSD-style |
| 5 | // license that can be found in the LICENSE file. |
| 6 | |
| 7 | // Check that we do loads exactly once. The SSA backend |
| 8 | // once tried to do the load in f twice, once sign extended |
| 9 | // and once zero extended. This can cause problems in |
| 10 | // racy code, particularly sync/mutex. |
| 11 | |
| 12 | package main |
| 13 | |
| 14 | func f(p *byte) bool { |
| 15 | x := *p |
| 16 | a := int64(int8(x)) |
| 17 | b := int64(uint8(x)) |
| 18 | return a == b |
| 19 | } |
| 20 | |
| 21 | func main() { |
| 22 | var x byte |
| 23 | const N = 1000000 |
| 24 | c := make(chan struct{}) |
| 25 | go func() { |
| 26 | for i := 0; i < N; i++ { |
| 27 | x = 1 |
| 28 | } |
| 29 | c <- struct{}{} |
| 30 | }() |
| 31 | go func() { |
| 32 | for i := 0; i < N; i++ { |
| 33 | x = 2 |
| 34 | } |
| 35 | c <- struct{}{} |
| 36 | }() |
| 37 | |
| 38 | for i := 0; i < N; i++ { |
| 39 | if !f(&x) { |
| 40 | panic("non-atomic load!") |
| 41 | } |
| 42 | } |
| 43 | <-c |
| 44 | <-c |
| 45 | } |