RFR: 8286972: Support the new loop induction variable related PopulateIndex IR node on x86

[Sandhya Viswanathan]

On Wed, 18 May 2022 23:51:07 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> This PR adds x86 backend support for the new loop induction variable related PopulateIndex IR node. 
>> This IR node was added as part of [JDK-8280510](https://bugs.openjdk.java.net/browse/JDK-8280510).
>> 
>> The performance numbers are as follows:
>> Before:
>> Benchmark                   (count)   Mode  Cnt       Score       Error  Units
>> IndexVector.exprWithIndex1    65536  thrpt    3   64556.552 ±  1126.396  ops/s
>> IndexVector.exprWithIndex2    65536  thrpt    3   22117.050 ± 11452.098  ops/s
>> IndexVector.indexArrayFill    65536  thrpt    3  117776.383 ±  1120.957  ops/s
>> 
>> After:
>> Benchmark                   (count)   Mode  Cnt       Score       Error  Units
>> IndexVector.exprWithIndex1    65536  thrpt    3  203180.290 ±  2147.807  ops/s
>> IndexVector.exprWithIndex2    65536  thrpt    3  274132.756 ±  6853.393  ops/s
>> IndexVector.indexArrayFill    65536  thrpt    3  374165.202 ± 46930.779  ops/s
>> 
>> Please review.
>> 
>> Best Regards,
>> Sandhya
>
> src/hotspot/cpu/x86/x86.ad line 1475:
> 
>> 1473:         return false;
>> 1474:       }
>> 1475:       // fallthrough
> 
> Please, don't do `fallthrough` - `RoundVF` is not related to `PopulateIndex`. Why not `if (!is_LP64 || UseAVX < 2)`?
> Are there limitations in 32 bits or you don't want spend time on not major platform (which is also understandable)?

It is not a major platform so I didn't spend time on it.

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PR: https://git.openjdk.java.net/jdk/pull/8778