RFR: 8286972: Support the new loop induction variable related PopulateIndex IR node on x86 [v5]

[Fei Gao]

On Fri, 20 May 2022 05:09:41 GMT, Sandhya Viswanathan <sviswanathan 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
>
> Sandhya Viswanathan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comment resolution

src/hotspot/cpu/x86/x86.ad line 8270:

> 8268:   ins_encode %{
> 8269:      assert($src2$$constant == 1, "required");
> 8270:      int vlen = Matcher::vector_length(this);

May I ask why use `Matcher::vector_length()` here, rather than `Matcher::vector_length_in_bytes()`, for `load_iota_indices()`? Thanks.

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