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regexp: don't allocate when All methods find no matches

name                old time/op    new time/op    delta
FindAllNoMatches-8     216ns ± 3%     122ns ± 2%   -43.52%  (p=0.000 n=10+10)

name                old alloc/op   new alloc/op   delta
FindAllNoMatches-8      240B ± 0%        0B       -100.00%  (p=0.000 n=10+10)

name                old allocs/op  new allocs/op  delta
FindAllNoMatches-8      1.00 ± 0%      0.00       -100.00%  (p=0.000 n=10+10)

This work was supported by Sourcegraph.

Change-Id: I30aac201370ccfb40a6ff637402020ac20f61f70
Reviewed-on: https://go-review.googlesource.com/87418
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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josharian authored and bradfitz committed Dec 18, 2017
1 parent 4b8a7ea commit df5997b99b9a89e1198596366230fa6c4dd50b70
Showing with 45 additions and 32 deletions.
  1. +13 −0 src/regexp/all_test.go
  2. +32 −32 src/regexp/regexp.go
@@ -581,6 +581,19 @@ func BenchmarkFind(b *testing.B) {
}
}
func BenchmarkFindAllNoMatches(b *testing.B) {
re := MustCompile("a+b+")
s := []byte("acddee")
b.ReportAllocs()
b.ResetTimer()
for i := 0; i < b.N; i++ {
all := re.FindAll(s, -1)
if all != nil {
b.Fatalf("FindAll(%q) = %q; want nil", s, all)
}
}
}
func BenchmarkFindString(b *testing.B) {
b.StopTimer()
re := MustCompile("a+b+")
@@ -984,13 +984,13 @@ func (re *Regexp) FindAll(b []byte, n int) [][]byte {
if n < 0 {
n = len(b) + 1
}
result := make([][]byte, 0, startSize)
var result [][]byte
re.allMatches("", b, n, func(match []int) {
if result == nil {
result = make([][]byte, 0, startSize)
}
result = append(result, b[match[0]:match[1]])
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1002,13 +1002,13 @@ func (re *Regexp) FindAllIndex(b []byte, n int) [][]int {
if n < 0 {
n = len(b) + 1
}
result := make([][]int, 0, startSize)
var result [][]int
re.allMatches("", b, n, func(match []int) {
if result == nil {
result = make([][]int, 0, startSize)
}
result = append(result, match[0:2])
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1020,13 +1020,13 @@ func (re *Regexp) FindAllString(s string, n int) []string {
if n < 0 {
n = len(s) + 1
}
result := make([]string, 0, startSize)
var result []string
re.allMatches(s, nil, n, func(match []int) {
if result == nil {
result = make([]string, 0, startSize)
}
result = append(result, s[match[0]:match[1]])
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1038,13 +1038,13 @@ func (re *Regexp) FindAllStringIndex(s string, n int) [][]int {
if n < 0 {
n = len(s) + 1
}
result := make([][]int, 0, startSize)
var result [][]int
re.allMatches(s, nil, n, func(match []int) {
if result == nil {
result = make([][]int, 0, startSize)
}
result = append(result, match[0:2])
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1056,8 +1056,11 @@ func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
if n < 0 {
n = len(b) + 1
}
result := make([][][]byte, 0, startSize)
var result [][][]byte
re.allMatches("", b, n, func(match []int) {
if result == nil {
result = make([][][]byte, 0, startSize)
}
slice := make([][]byte, len(match)/2)
for j := range slice {
if match[2*j] >= 0 {
@@ -1066,9 +1069,6 @@ func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
}
result = append(result, slice)
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1080,13 +1080,13 @@ func (re *Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int {
if n < 0 {
n = len(b) + 1
}
result := make([][]int, 0, startSize)
var result [][]int
re.allMatches("", b, n, func(match []int) {
if result == nil {
result = make([][]int, 0, startSize)
}
result = append(result, match)
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1098,8 +1098,11 @@ func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
if n < 0 {
n = len(s) + 1
}
result := make([][]string, 0, startSize)
var result [][]string
re.allMatches(s, nil, n, func(match []int) {
if result == nil {
result = make([][]string, 0, startSize)
}
slice := make([]string, len(match)/2)
for j := range slice {
if match[2*j] >= 0 {
@@ -1108,9 +1111,6 @@ func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
}
result = append(result, slice)
})
if len(result) == 0 {
return nil
}
return result
}
@@ -1123,13 +1123,13 @@ func (re *Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int {
if n < 0 {
n = len(s) + 1
}
result := make([][]int, 0, startSize)
var result [][]int
re.allMatches(s, nil, n, func(match []int) {
if result == nil {
result = make([][]int, 0, startSize)
}
result = append(result, match)
})
if len(result) == 0 {
return nil
}
return result
}

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