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strings: add special cases for Join of 2 and 3 strings

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We already had special cases for 0 and 1. Add 2 and 3 for now too.
To be removed if the compiler is improved later (#6714).

This halves the number of allocations and total bytes allocated via
common filepath.Join calls, improving filepath.Walk performance.

Noticed as part of investigating filepath.Walk in #16399.

Change-Id: If7b1bb85606d4720f3ebdf8de7b1e12ad165079d
Reviewed-on: https://go-review.googlesource.com/25005
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Brad Fitzpatrick 2016-07-18 17:27:21 +00:00
parent c88e868030
commit 3ddc9ad916
1 changed files with 11 additions and 3 deletions
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14
src/strings/strings.go
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@ -342,11 +342,19 @@ func FieldsFunc(s string, f func(rune) bool) []string {
// Join concatenates the elements of a to create a single string. The separator string
// sep is placed between elements in the resulting string.
func Join(a []string, sep string) string {
if len(a) == 0 {
switch len(a) {
case 0:
return ""
}
if len(a) == 1 {
case 1:
return a[0]
case 2:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1]
case 3:
// Special case for common small values.
// Remove if golang.org/issue/6714 is fixed
return a[0] + sep + a[1] + sep + a[2]
}
n := len(sep) * (len(a) - 1)
for i := 0; i < len(a); i++ {