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

[Сергей Цыпанов]

My assumption is based on conclusions drawn from this article: https://shipilev.net/blog/2016/arrays-wisdom-ancients/

I don't think the situation has changed much since then.

However, I'll do separate benchmarking with the latest JDK just in case.

25.04.2019, 11:24, "Ivan Gerasimov" <ivan.gerasimov at oracle.com>:
> Hi Sergei!
>
> Thanks for sharing.
>
> However, it's not immediately obvious to me why the later is better than
> the former. Can you please elaborate on that?
>
> I think, it worth a separate discussion.
>
> With kind regards,
>
> Ivan
>
> On 4/25/19 12:40 AM, Сергей Цыпанов wrote:
>>  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
>
> --
> With kind regards,
> Ivan Gerasimov