RFR: 8327147: optimized implementation of round operation for x86_64 CPUs

Sat Mar 2 16:36:51 UTC 2024

On Fri, 1 Mar 2024 19:11:58 GMT, Srinivas Vamsi Parasa <duke at openjdk.org> wrote:

> The goal of this PR is to provide ~4x faster implementation of Math.ceil, Math.floor and Math.rint for x86_64 CPUs.
> 
> Below is the performance data on an Intel Tiger Lake machine. 
> 
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> 
> Benchmark | Stock JDK   (ops/ms) | This PR (ops/ms) | Speedup
> -- | -- | -- | --
> MathBench.ceilDouble | 547979 | 2170198 | 3.96
> MathBench.floorDouble | 547979 | 2167459 | 3.96
> MathBench.rintDouble | 547962 | 2130499 | 3.89
> 
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Changes requested by jbhateja (Reviewer).

src/hotspot/cpu/x86/x86.ad line 3884:

> 3882: 
> 3883: instruct roundD_reg_avx(legRegD dst, legRegD src, immU8 rmode) %{
> 3884:   predicate(UseAVX > 0);

can you push the predicate in instruction encoding block and fold this pattern with roundD_reg.

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PR Review: https://git.openjdk.org/jdk/pull/18089#pullrequestreview-1912689349
PR Review Comment: https://git.openjdk.org/jdk/pull/18089#discussion_r1510001900