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runtime: speed up growslice by avoiding divisions
Only compute the number of maximum allowed elements per slice once. Special case newcap computation for slices with byte sized elements. name old time/op new time/op delta GrowSliceBytes-2 61.1ns ± 1% 43.4ns ± 1% -29.00% (p=0.000 n=20+20) GrowSliceInts-2 85.9ns ± 1% 75.7ns ± 1% -11.80% (p=0.000 n=20+20) Change-Id: I5d9c0d5987cdd108ac29dc32e31912dcefa2324d Reviewed-on: https://go-review.googlesource.com/20653 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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@ -7,6 +7,24 @@ import "testing"
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const N = 20
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const N = 20
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func BenchmarkGrowSliceBytes(b *testing.B) {
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b.StopTimer()
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var x = make([]byte, 8)
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b.StartTimer()
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for i := 0; i < b.N; i++ {
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_ = append([]byte(nil), x...)
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}
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}
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func BenchmarkGrowSliceInts(b *testing.B) {
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b.StopTimer()
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var x = make([]int, 8)
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b.StartTimer()
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for i := 0; i < b.N; i++ {
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_ = append([]int(nil), x...)
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}
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}
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func BenchmarkAppend(b *testing.B) {
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func BenchmarkAppend(b *testing.B) {
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b.StopTimer()
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b.StopTimer()
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x := make([]int, 0, N)
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x := make([]int, 0, N)
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@ -38,10 +38,6 @@ func makeslice(t *slicetype, len64, cap64 int64) slice {
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// and it returns a new slice with at least that capacity, with the old data
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// and it returns a new slice with at least that capacity, with the old data
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// copied into it.
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// copied into it.
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func growslice(t *slicetype, old slice, cap int) slice {
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func growslice(t *slicetype, old slice, cap int) slice {
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if cap < old.cap || t.elem.size > 0 && uintptr(cap) > _MaxMem/t.elem.size {
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panic(errorString("growslice: cap out of range"))
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}
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if raceenabled {
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if raceenabled {
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callerpc := getcallerpc(unsafe.Pointer(&t))
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callerpc := getcallerpc(unsafe.Pointer(&t))
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racereadrangepc(old.array, uintptr(old.len*int(t.elem.size)), callerpc, funcPC(growslice))
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racereadrangepc(old.array, uintptr(old.len*int(t.elem.size)), callerpc, funcPC(growslice))
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@ -52,11 +48,19 @@ func growslice(t *slicetype, old slice, cap int) slice {
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et := t.elem
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et := t.elem
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if et.size == 0 {
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if et.size == 0 {
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if cap < old.cap {
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panic(errorString("growslice: cap out of range"))
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}
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// append should not create a slice with nil pointer but non-zero len.
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// append should not create a slice with nil pointer but non-zero len.
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// We assume that append doesn't need to preserve old.array in this case.
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// We assume that append doesn't need to preserve old.array in this case.
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return slice{unsafe.Pointer(&zerobase), old.len, cap}
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return slice{unsafe.Pointer(&zerobase), old.len, cap}
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}
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}
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maxcap := _MaxMem / et.size
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if cap < old.cap || uintptr(cap) > maxcap {
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panic(errorString("growslice: cap out of range"))
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}
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newcap := old.cap
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newcap := old.cap
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if newcap+newcap < cap {
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if newcap+newcap < cap {
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newcap = cap
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newcap = cap
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@ -73,12 +77,18 @@ func growslice(t *slicetype, old slice, cap int) slice {
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}
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}
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}
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}
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if uintptr(newcap) >= _MaxMem/et.size {
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if uintptr(newcap) >= maxcap {
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panic(errorString("growslice: cap out of range"))
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panic(errorString("growslice: cap out of range"))
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}
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}
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lenmem := uintptr(old.len) * et.size
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lenmem := uintptr(old.len) * et.size
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capmem := roundupsize(uintptr(newcap) * et.size)
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capmem := roundupsize(uintptr(newcap) * et.size)
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newcap = int(capmem / et.size)
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if et.size == 1 {
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newcap = int(capmem)
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} else {
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newcap = int(capmem / et.size)
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}
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var p unsafe.Pointer
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var p unsafe.Pointer
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if et.kind&kindNoPointers != 0 {
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if et.kind&kindNoPointers != 0 {
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p = rawmem(capmem)
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p = rawmem(capmem)
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