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

[Ivan Gerasimov]

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