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 // This test makes sure that we don't split a single 8 // load up into two separate loads. 9 10 package main 11 12 import "fmt" 13 14 //go:noinline 15 func read1(b []byte) (uint16, uint16) { 16 // There is only a single read of b[0]. The two 17 // returned values must have the same low byte. 18 v := b[0] 19 return uint16(v), uint16(v) | uint16(b[1])<<8 20 } 21 22 const N = 100000 23 24 func main1() { 25 done := make(chan struct{}) 26 b := make([]byte, 2) 27 go func() { 28 for i := 0; i < N; i++ { 29 b[0] = byte(i) 30 b[1] = byte(i) 31 } 32 done <- struct{}{} 33 }() 34 go func() { 35 for i := 0; i < N; i++ { 36 x, y := read1(b) 37 if byte(x) != byte(y) { 38 fmt.Printf("x=%x y=%x\n", x, y) 39 panic("bad") 40 } 41 } 42 done <- struct{}{} 43 }() 44 <-done 45 <-done 46 } 47 48 //go:noinline 49 func read2(b []byte) (uint16, uint16) { 50 // There is only a single read of b[1]. The two 51 // returned values must have the same high byte. 52 v := uint16(b[1]) << 8 53 return v, uint16(b[0]) | v 54 } 55 56 func main2() { 57 done := make(chan struct{}) 58 b := make([]byte, 2) 59 go func() { 60 for i := 0; i < N; i++ { 61 b[0] = byte(i) 62 b[1] = byte(i) 63 } 64 done <- struct{}{} 65 }() 66 go func() { 67 for i := 0; i < N; i++ { 68 x, y := read2(b) 69 if x&0xff00 != y&0xff00 { 70 fmt.Printf("x=%x y=%x\n", x, y) 71 panic("bad") 72 } 73 } 74 done <- struct{}{} 75 }() 76 <-done 77 <-done 78 } 79 80 func main() { 81 main1() 82 main2() 83 } 84
