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regexp: reduce mallocs in Regexp.Find* and Regexp.ReplaceAll*.

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This improves Regexp.Find* and Regexp.ReplaceAll* speed:

name                  old time/op    new time/op    delta
Find-4                   345ns ± 1%     314ns ± 1%    -8.94%    (p=0.000 n=9+8)
FindString-4             341ns ± 1%     308ns ± 0%    -9.85%   (p=0.000 n=10+9)
FindSubmatch-4           440ns ± 1%     404ns ± 0%    -8.27%   (p=0.000 n=10+8)
FindStringSubmatch-4     426ns ± 0%     387ns ± 0%    -9.07%   (p=0.000 n=10+9)
ReplaceAll-4            1.75µs ± 1%    1.67µs ± 0%    -4.45%   (p=0.000 n=9+10)

name                  old alloc/op   new alloc/op   delta
Find-4                   16.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.000 n=10+10)
FindString-4             16.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.000 n=10+10)
FindSubmatch-4           80.0B ± 0%     48.0B ± 0%   -40.00%  (p=0.000 n=10+10)
FindStringSubmatch-4     64.0B ± 0%     32.0B ± 0%   -50.00%  (p=0.000 n=10+10)
ReplaceAll-4              152B ± 0%      104B ± 0%   -31.58%  (p=0.000 n=10+10)

name                  old allocs/op  new allocs/op  delta
Find-4                    1.00 ± 0%     0.00 ±NaN%  -100.00%  (p=0.000 n=10+10)
FindString-4              1.00 ± 0%     0.00 ±NaN%  -100.00%  (p=0.000 n=10+10)
FindSubmatch-4            2.00 ± 0%      1.00 ± 0%   -50.00%  (p=0.000 n=10+10)
FindStringSubmatch-4      2.00 ± 0%      1.00 ± 0%   -50.00%  (p=0.000 n=10+10)
ReplaceAll-4              8.00 ± 0%      5.00 ± 0%   -37.50%  (p=0.000 n=10+10)

Fixes #15643

Change-Id: I594fe51172373e2adb98d1d25c76ca2cde54ff48
Reviewed-on: https://go-review.googlesource.com/23030
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Aliaksandr Valialkin 2016-05-11 14:57:24 +03:00 • committed by Brad Fitzpatrick
parent 5923df1af9
commit bea39e63ec
3 changed files with 104 additions and 28 deletions
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31
src/regexp/exec.go
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@ -405,14 +405,16 @@ func (m *machine) onepass(i input, pos int) bool {
return m.matched
}
// empty is a non-nil 0-element slice,
// so doExecute can avoid an allocation
// when 0 captures are requested from a successful match.
var empty = make([]int, 0)
// doMatch reports whether either r, b or s match the regexp.
func (re *Regexp) doMatch(r io.RuneReader, b []byte, s string) bool {
return re.doExecute(r, b, s, 0, 0, nil) != nil
}
// doExecute finds the leftmost match in the input and returns
// the position of its subexpressions.
func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int) []int {
// doExecute finds the leftmost match in the input, appends the position
// of its subexpressions to dstCap and returns dstCap.
//
// nil is returned if no matches are found and non-nil if matches are found.
func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int, dstCap []int) []int {
m := re.get()
var i input
var size int
@ -445,12 +447,15 @@ func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap i
return nil
}
}
if ncap == 0 {
re.put(m)
return empty // empty but not nil
dstCap = append(dstCap, m.matchcap...)
if dstCap == nil {
// Keep the promise of returning non-nil value on match.
dstCap = arrayNoInts[:0]
}
cap := make([]int, len(m.matchcap))
copy(cap, m.matchcap)
re.put(m)
return cap
return dstCap
}
// arrayNoInts is returned by doExecute match if nil dstCap is passed
// to it with ncap=0.
var arrayNoInts [0]int