RFR 8222955 : Optimize String.replace(CharSequence, CharSequence) for Latin1 encoded strings

[Сергей Цыпанов]

Hi Ivan,

recently looking into java.lang.String I've found out that String::split still uses old collection-to-array approach:

String[] result = new String[resultSize];
return list.subList(0, resultSize).toArray(result);

which should be replaced with 

return list.subList(0, resultSize).toArray(new String[0]);

this changes is too small to create a separate ticket for this, so could I ask you to add this into your changes?

Regards,
Sergei Tsypanov


25.04.2019, 08:04, "Ivan Gerasimov" <ivan.gerasimov at oracle.com>:
> Hello!
>
> This enhancement was inspired by a recent discussion at
> compiler-dev at openjdk.java.net.
>
> It seems to be a non-uncommon situation when String.replace(CS, CS) is
> called with this and both arguments being Latin1 strings, so it seems
> reasonable to optimize for such case.
>
> Here are the fresh benchmark results (see the webrev for the source of
> the benchmark):
> -- prior the fix:
> Benchmark Mode Cnt Score Error Units
> StringReplace.replace1_0 avgt 24 70.860 ± 5.239 ns/op
> StringReplace.replace1_1 avgt 24 82.661 ± 1.007 ns/op
> StringReplace.replace1_2 avgt 24 97.251 ± 1.186 ns/op
>
> -- after the fix:
> Benchmark Mode Cnt Score Error Units
> StringReplace.replace1_0 avgt 24 52.855 ± 0.982 ns/op
> StringReplace.replace1_1 avgt 24 23.849 ± 0.066 ns/op
> StringReplace.replace1_2 avgt 24 62.266 ± 0.552 ns/op
>
> So the speedup was x1.3, x3.4, x1.5.
>
> Would you please help review the fix?
>
> BUGURL: https://bugs.openjdk.java.net/browse/JDK-8222955
> WEBREV: http://cr.openjdk.java.net/~igerasim/8222955/00/webrev/
>
> Mach5 job is in progress and looks green so far (a few test groups are
> left).
>
> Thanks in advance!
>
> --
> With kind regards,
> Ivan Gerasimov