RFR: 8365205: C2: Optimize popcount value computation using knownbits [v12]

[Quan Anh Mai]

On Sat, 4 Oct 2025 06:01:07 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> This patch optimizes PopCount value transforms using KnownBits information.
>> Following are the results of the micro-benchmark included with the patch
>> 
>> 
>> 
>> System: 13th Gen Intel(R) Core(TM) i3-1315U
>> 
>> Baseline:
>> Benchmark                                      Mode  Cnt       Score   Error  Units
>> PopCountValueTransform.LogicFoldingKerenLong  thrpt    2  215460.670          ops/s
>> PopCountValueTransform.LogicFoldingKerenlInt  thrpt    2  294014.826          ops/s
>> 
>> Withopt:
>> Benchmark                                      Mode  Cnt       Score   Error  Units
>> PopCountValueTransform.LogicFoldingKerenLong  thrpt    2  389978.082          ops/s
>> PopCountValueTransform.LogicFoldingKerenlInt  thrpt    2  417261.583          ops/s
>> 
>> 
>> Kindly review and share your feedback.
>> 
>> Best Regards,
>> Jatin
>
> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review comments resolution

LGTM otherwise

src/hotspot/share/opto/countbitsnode.cpp line 144:

> 142:     return Type::TOP;
> 143:   }
> 144:   const TypeInt* tint = t->isa_int();

This should be `is_int`. `isa_int` is fine, but in cases of unexpected types, it will SIGSEGV instead of throwing an assertion, which is more difficult to debug.

-------------

Marked as reviewed by qamai (Committer).

PR Review: https://git.openjdk.org/jdk/pull/27075#pullrequestreview-3305634424
PR Review Comment: https://git.openjdk.org/jdk/pull/27075#discussion_r2407155945