RFR: 8365205: C2: Optimize popcount value computation using knownbits [v3]

[Jatin Bhateja]

> 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
> PopCountValueTransform.StockKernelInt         thrpt    2  409295.875          ops/s
> PopCountValueTransform.StockKernelLong        thrpt    2  368025.608          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
> PopCountValueTransform.StockKernelInt         thrpt    2  418649.269          ops/s
> PopCountValueTransform.StockKernelLong        thrpt    2  381330.221          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:

  Update countbitsnode.cpp

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27075/files
  - new: https://git.openjdk.org/jdk/pull/27075/files/a68fbc08..52ae6bc8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27075&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27075&range=01-02

  Stats: 9 lines in 1 file changed: 0 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/27075.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27075/head:pull/27075

PR: https://git.openjdk.org/jdk/pull/27075