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bytes, strings: avoid unnecessary zero initialization
Add bytealg.MakeNoZero that specially allocates a []byte without zeroing it. It assumes the caller will populate every byte. From within the bytes and strings packages, we can use bytealg.MakeNoZero in a way where our logic ensures that the entire slice is overwritten such that uninitialized bytes are never leaked to the end user. We use bytealg.MakeNoZero from within the following functions: * bytes.Join * bytes.Repeat * bytes.ToUpper * bytes.ToLower * strings.Builder.Grow The optimization in strings.Builder transitively benefits the following: * strings.Join * strings.Map * strings.Repeat * strings.ToUpper * strings.ToLower * strings.ToValidUTF8 * strings.Replace * any user logic that depends on strings.Builder This optimization is especially notable on large buffers that do not fit in the CPU cache, such that the cost of runtime.memclr and runtime.memmove are non-trivial since they are both limited by the relatively slow speed of physical RAM. Performance: RepeatLarge/256/1 66.0ns ± 3% 64.5ns ± 1% ~ (p=0.095 n=5+5) RepeatLarge/256/16 55.4ns ± 5% 53.1ns ± 3% -4.17% (p=0.016 n=5+5) RepeatLarge/512/1 95.5ns ± 7% 87.1ns ± 2% -8.78% (p=0.008 n=5+5) RepeatLarge/512/16 84.4ns ± 9% 76.2ns ± 5% -9.73% (p=0.016 n=5+5) RepeatLarge/1024/1 161ns ± 4% 144ns ± 7% -10.45% (p=0.016 n=5+5) RepeatLarge/1024/16 148ns ± 3% 141ns ± 5% ~ (p=0.095 n=5+5) RepeatLarge/2048/1 296ns ± 7% 288ns ± 5% ~ (p=0.841 n=5+5) RepeatLarge/2048/16 298ns ± 8% 281ns ± 5% ~ (p=0.151 n=5+5) RepeatLarge/4096/1 593ns ± 8% 539ns ± 8% -8.99% (p=0.032 n=5+5) RepeatLarge/4096/16 568ns ±12% 526ns ± 7% ~ (p=0.056 n=5+5) RepeatLarge/8192/1 1.15µs ± 8% 1.08µs ±12% ~ (p=0.095 n=5+5) RepeatLarge/8192/16 1.12µs ± 4% 1.07µs ± 7% ~ (p=0.310 n=5+5) RepeatLarge/8192/4097 1.77ns ± 1% 1.76ns ± 2% ~ (p=0.310 n=5+5) RepeatLarge/16384/1 2.06µs ± 7% 1.94µs ± 5% ~ (p=0.222 n=5+5) RepeatLarge/16384/16 2.02µs ± 4% 1.92µs ± 6% ~ (p=0.095 n=5+5) RepeatLarge/16384/4097 1.50µs ±15% 1.44µs ±11% ~ (p=0.802 n=5+5) RepeatLarge/32768/1 3.90µs ± 8% 3.65µs ±11% ~ (p=0.151 n=5+5) RepeatLarge/32768/16 3.92µs ±14% 3.68µs ±12% ~ (p=0.222 n=5+5) RepeatLarge/32768/4097 3.71µs ± 5% 3.43µs ± 4% -7.54% (p=0.032 n=5+5) RepeatLarge/65536/1 7.47µs ± 8% 6.88µs ± 9% ~ (p=0.056 n=5+5) RepeatLarge/65536/16 7.29µs ± 4% 6.74µs ± 6% -7.60% (p=0.016 n=5+5) RepeatLarge/65536/4097 7.90µs ±11% 6.34µs ± 5% -19.81% (p=0.008 n=5+5) RepeatLarge/131072/1 17.0µs ±18% 14.1µs ± 6% -17.32% (p=0.008 n=5+5) RepeatLarge/131072/16 15.2µs ± 2% 16.2µs ±17% ~ (p=0.151 n=5+5) RepeatLarge/131072/4097 15.7µs ± 6% 14.8µs ±11% ~ (p=0.095 n=5+5) RepeatLarge/262144/1 30.4µs ± 5% 31.4µs ±13% ~ (p=0.548 n=5+5) RepeatLarge/262144/16 30.1µs ± 4% 30.7µs ±11% ~ (p=1.000 n=5+5) RepeatLarge/262144/4097 31.2µs ± 7% 32.7µs ±13% ~ (p=0.310 n=5+5) RepeatLarge/524288/1 67.5µs ± 9% 63.7µs ± 3% ~ (p=0.095 n=5+5) RepeatLarge/524288/16 67.2µs ± 5% 62.9µs ± 6% ~ (p=0.151 n=5+5) RepeatLarge/524288/4097 65.5µs ± 4% 65.2µs ±18% ~ (p=0.548 n=5+5) RepeatLarge/1048576/1 141µs ± 6% 137µs ±14% ~ (p=0.421 n=5+5) RepeatLarge/1048576/16 140µs ± 2% 134µs ±11% ~ (p=0.222 n=5+5) RepeatLarge/1048576/4097 141µs ± 3% 134µs ±10% ~ (p=0.151 n=5+5) RepeatLarge/2097152/1 258µs ± 2% 271µs ±10% ~ (p=0.222 n=5+5) RepeatLarge/2097152/16 263µs ± 6% 273µs ± 9% ~ (p=0.151 n=5+5) RepeatLarge/2097152/4097 270µs ± 2% 277µs ± 6% ~ (p=0.690 n=5+5) RepeatLarge/4194304/1 684µs ± 3% 467µs ± 6% -31.69% (p=0.008 n=5+5) RepeatLarge/4194304/16 682µs ± 1% 471µs ± 7% -30.91% (p=0.008 n=5+5) RepeatLarge/4194304/4097 685µs ± 2% 465µs ±20% -32.12% (p=0.008 n=5+5) RepeatLarge/8388608/1 1.50ms ± 1% 1.16ms ± 8% -22.63% (p=0.008 n=5+5) RepeatLarge/8388608/16 1.50ms ± 2% 1.22ms ±17% -18.49% (p=0.008 n=5+5) RepeatLarge/8388608/4097 1.51ms ± 7% 1.33ms ±11% -11.56% (p=0.008 n=5+5) RepeatLarge/16777216/1 3.48ms ± 4% 2.66ms ±13% -23.76% (p=0.008 n=5+5) RepeatLarge/16777216/16 3.37ms ± 3% 2.57ms ±13% -23.72% (p=0.008 n=5+5) RepeatLarge/16777216/4097 3.38ms ± 9% 2.50ms ±11% -26.16% (p=0.008 n=5+5) RepeatLarge/33554432/1 7.74ms ± 1% 4.70ms ±19% -39.31% (p=0.016 n=4+5) RepeatLarge/33554432/16 7.90ms ± 4% 4.78ms ± 9% -39.50% (p=0.008 n=5+5) RepeatLarge/33554432/4097 7.80ms ± 2% 4.86ms ±11% -37.60% (p=0.008 n=5+5) RepeatLarge/67108864/1 16.4ms ± 3% 9.7ms ±15% -41.29% (p=0.008 n=5+5) RepeatLarge/67108864/16 16.5ms ± 1% 9.9ms ±15% -39.83% (p=0.008 n=5+5) RepeatLarge/67108864/4097 16.5ms ± 1% 11.0ms ±18% -32.95% (p=0.008 n=5+5) RepeatLarge/134217728/1 35.2ms ±12% 19.2ms ±10% -45.58% (p=0.008 n=5+5) RepeatLarge/134217728/16 34.6ms ± 6% 19.3ms ± 7% -44.07% (p=0.008 n=5+5) RepeatLarge/134217728/4097 33.2ms ± 2% 19.3ms ±14% -41.79% (p=0.008 n=5+5) RepeatLarge/268435456/1 70.9ms ± 2% 36.2ms ± 5% -48.87% (p=0.008 n=5+5) RepeatLarge/268435456/16 77.4ms ± 7% 36.1ms ± 8% -53.33% (p=0.008 n=5+5) RepeatLarge/268435456/4097 75.8ms ± 4% 37.0ms ± 4% -51.15% (p=0.008 n=5+5) RepeatLarge/536870912/1 163ms ±14% 77ms ± 9% -52.94% (p=0.008 n=5+5) RepeatLarge/536870912/16 156ms ± 4% 76ms ± 6% -51.42% (p=0.008 n=5+5) RepeatLarge/536870912/4097 151ms ± 2% 76ms ± 6% -49.64% (p=0.008 n=5+5) RepeatLarge/1073741824/1 293ms ± 5% 149ms ± 8% -49.18% (p=0.008 n=5+5) RepeatLarge/1073741824/16 308ms ± 9% 150ms ± 8% -51.19% (p=0.008 n=5+5) RepeatLarge/1073741824/4097 299ms ± 5% 151ms ± 6% -49.51% (p=0.008 n=5+5) Updates #57153 Change-Id: I024553b7e676d6da6408278109ac1fa8def0a802 Reviewed-on: https://go-review.googlesource.com/c/go/+/456336 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com> Run-TryBot: Joseph Tsai <joetsai@digital-static.net> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
This commit is contained in:
Joe Tsai
Joseph Tsai
parent
9a199d42da
commit
132fae93b7
5 changed files with 57 additions and 22 deletions
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@ -13,6 +13,8 @@ import (
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"unicode/utf8"
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)
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const maxInt = int(^uint(0) >> 1)
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// explode splits s into a slice of UTF-8 strings,
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// one string per Unicode character up to a maximum of n (n < 0 means no limit).
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// Invalid UTF-8 bytes are sliced individually.
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@ -436,9 +438,19 @@ func Join(elems []string, sep string) string {
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case 1:
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return elems[0]
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}
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n := len(sep) * (len(elems) - 1)
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for i := 0; i < len(elems); i++ {
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n += len(elems[i])
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var n int
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if len(sep) > 0 {
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if len(sep) >= maxInt/(len(elems)-1) {
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panic("strings: Join output length overflow")
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}
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n += len(sep) * (len(elems) - 1)
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}
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for _, elem := range elems {
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if len(elem) > maxInt-n {
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panic("strings: Join output length overflow")
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}
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n += len(elem)
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}
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var b Builder
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@ -536,21 +548,20 @@ func Repeat(s string, count int) string {
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}
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// Since we cannot return an error on overflow,
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// we should panic if the repeat will generate
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// an overflow.
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// we should panic if the repeat will generate an overflow.
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// See golang.org/issue/16237.
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if count < 0 {
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panic("strings: negative Repeat count")
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} else if len(s)*count/count != len(s) {
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panic("strings: Repeat count causes overflow")
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}
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if len(s) >= maxInt/count {
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panic("strings: Repeat output length overflow")
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}
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n := len(s) * count
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if len(s) == 0 {
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return ""
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}
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n := len(s) * count
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// Past a certain chunk size it is counterproductive to use
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// larger chunks as the source of the write, as when the source
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// is too large we are basically just thrashing the CPU D-cache.
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