github.com/ltltlt/go-source-code@v0.0.0-20190830023027-95be009773aa/cmd/compile/internal/gc/testdata/dupLoad.go (about)

     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  }