strings: optimize Replace

[rui314]

What does 'go version' print?
go version devel +62052ebe728b Sun Mar 23 18:58:35 2014 -0700 linux/amd64

We have a patch to improve performance of string.Replace by adding a fast path
(https://golang.org/cl/79200044). We cannot commit this now because of the
feature freeze for Go 1.3. Needs to be reviewed after 1.3.

This is a benchmark result of the patch:

benchmark                        old ns/op    new ns/op    delta
BenchmarkGenericNoMatch               2691          774  -71.24%
BenchmarkGenericMatch1                7920         8151   +2.92%
BenchmarkGenericMatch2               52336        39927  -23.71%
BenchmarkSingleMaxSkipping            1575         1575   +0.00%
BenchmarkSingleLongSuffixFail         1429         1429   +0.00%
BenchmarkSingleMatch                 56228        55444   -1.39%
BenchmarkByteByteNoMatch               568          568   +0.00%
BenchmarkByteByteMatch                 977          972   -0.51%
BenchmarkByteStringMatch              1669         1687   +1.08%
BenchmarkHTMLEscapeNew                 422          422   +0.00%
BenchmarkHTMLEscapeOld                 692          670   -3.18%
BenchmarkByteByteReplaces             8492         8474   -0.21%
BenchmarkByteByteMap                  2817         2808   -0.32%

benchmark                         old MB/s     new MB/s  speedup
BenchmarkSingleMaxSkipping         6345.25      6346.76    1.00x
BenchmarkSingleLongSuffixFail       700.85       700.85    1.00x
BenchmarkSingleMatch                266.77       270.54    1.01x

[mikioh]

Comment 1:

Labels changed: added repo-main, release-go1.4.

[ccahoon]

Comment 2:

I believe this issue could have been closed by revision a58e16be34cb.

[ianlancetaylor]

Comment 3:

Thanks for the note.

Status changed to Fixed.