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runtime: avoid using REP prefix for IndexByte

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REP-prefixed instructions have a large startup cost.
Avoid them like the plague.

benchmark                  old ns/op     new ns/op     delta
BenchmarkIndexByte10-8     22.4          5.34          -76.16%

Fixes #13983

Change-Id: I857e956e240fc9681d053f2584ccf24c1b272bb3
Reviewed-on: https://go-review.googlesource.com/18703
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Keith Randall 2016-01-15 18:17:09 -08:00
parent a337e30620
commit 687abca1ea
2 changed files with 110 additions and 71 deletions
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37
src/bytes/bytes_test.go
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@ -335,6 +335,41 @@ func TestIndexByteBig(t *testing.T) {
}
}
// test a small index across all page offsets
func TestIndexByteSmall(t *testing.T) {
b := make([]byte, 5015) // bigger than a page
// Make sure we find the correct byte even when straddling a page.
for i := 0; i <= len(b)-15; i++ {
for j := 0; j < 15; j++ {
b[i+j] = byte(100 + j)
}
for j := 0; j < 15; j++ {
p := IndexByte(b[i:i+15], byte(100+j))
if p != j {
t.Errorf("IndexByte(%q, %d) = %d", b[i:i+15], 100+j, p)
}
}
for j := 0; j < 15; j++ {
b[i+j] = 0
}
}
// Make sure matches outside the slice never trigger.
for i := 0; i <= len(b)-15; i++ {
for j := 0; j < 15; j++ {
b[i+j] = 1
}
for j := 0; j < 15; j++ {
p := IndexByte(b[i:i+15], byte(0))
if p != -1 {
t.Errorf("IndexByte(%q, %d) = %d", b[i:i+15], 0, p)
}
}
for j := 0; j < 15; j++ {
b[i+j] = 0
}
}
}
func TestIndexRune(t *testing.T) {
for _, tt := range indexRuneTests {
a := []byte(tt.a)
@ -348,10 +383,12 @@ func TestIndexRune(t *testing.T) {
var bmbuf []byte
func BenchmarkIndexByte10(b *testing.B) { bmIndexByte(b, IndexByte, 10) }
func BenchmarkIndexByte32(b *testing.B) { bmIndexByte(b, IndexByte, 32) }
func BenchmarkIndexByte4K(b *testing.B) { bmIndexByte(b, IndexByte, 4<<10) }
func BenchmarkIndexByte4M(b *testing.B) { bmIndexByte(b, IndexByte, 4<<20) }
func BenchmarkIndexByte64M(b *testing.B) { bmIndexByte(b, IndexByte, 64<<20) }
func BenchmarkIndexBytePortable10(b *testing.B) { bmIndexByte(b, IndexBytePortable, 10) }
func BenchmarkIndexBytePortable32(b *testing.B) { bmIndexByte(b, IndexBytePortable, 32) }
func BenchmarkIndexBytePortable4K(b *testing.B) { bmIndexByte(b, IndexBytePortable, 4<<10) }
func BenchmarkIndexBytePortable4M(b *testing.B) { bmIndexByte(b, IndexBytePortable, 4<<20) }