RFR: 8254782: Fix benchmark issues in java/lang/StringIndexOfChar.java benchmark

[Claes Redestad]

On Wed, 28 Oct 2020 21:59:53 GMT, Jason Tatton <github.com+70893615+jasontatton-aws at openjdk.org> wrote:

> Please review the improvements which I have made to the java/lang/StringIndexOfChar.java jmh benchmark. Please let me know if any further improvements are required.
> 
> Thanks,
> Jason

Looks OK.

FWIW the current looping scheme look like what the [SafeLooping.measureWrong_2](https://github.com/openjdk/jmh/blob/620036ec27db3503fa2dee476036b3219c9a38bc/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_34_SafeLooping.java#L115) warns us about, and could possibly be improved by taking cues from [SafeLooping.measureRight_1](https://github.com/openjdk/jmh/blob/620036ec27db3503fa2dee476036b3219c9a38bc/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_34_SafeLooping.java#L136) and sink each `what.indexOf(..)` into a `BlackHole`. This might matter here since each unit of work is quite small. 

I'll approve the patch as-is, but please consider making those changes.

test/micro/org/openjdk/bench/java/lang/StringIndexOfChar.java line 63:

> 61:     private String [] utf16_sse4;
> 62:     private String [] utf16_avx2;
> 63:     private String [] utf16_mixedLength;

I'd be a little bit happier with `String[]` rather than `String []`

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Marked as reviewed by redestad (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/918