On Wed, 25 Jun 2025 09:16:48 GMT, Xiaohong Gong <xg...@openjdk.org> wrote:
>> JDK-8318650 introduced hotspot intrinsification of subword gather load APIs >> for X86 platforms [1]. However, the current implementation is not optimal >> for AArch64 SVE platform, which natively supports vector instructions for >> subword gather load operations using an int vector for indices (see [2][3]). >> >> Two key areas require improvement: >> 1. At the Java level, vector indices generated for range validation could be >> reused for the subsequent gather load operation on architectures with native >> vector instructions like AArch64 SVE. However, the current implementation >> prevents compiler reuse of these index vectors due to divergent control >> flow, potentially impacting performance. >> 2. At the compiler IR level, the additional `offset` input for >> `LoadVectorGather`/`LoadVectorGatherMasked` with subword types increases IR >> complexity and complicates backend implementation. Furthermore, generating >> `add` instructions before each memory access negatively impacts performance. >> >> This patch refactors the implementation at both the Java level and compiler >> mid-end to improve efficiency and maintainability across different >> architectures. >> >> Main changes: >> 1. Java-side API refactoring: >> - Explicitly passes generated index vectors to hotspot, eliminating >> duplicate index vectors for gather load instructions on >> architectures like AArch64. >> 2. C2 compiler IR refactoring: >> - Refactors `LoadVectorGather`/`LoadVectorGatherMasked` IR for subword >> types by removing the memory offset input and incorporating it into the >> memory base `addr` at the IR level. This simplifies backend implementation, >> reduces add operations, and unifies the IR across all types. >> 3. Backend changes: >> - Streamlines X86 implementation of subword gather operations following >> the removal of the offset input from the IR level. >> >> Performance: >> The performance of the relative JMH improves up to 27% on a X86 AVX512 >> system. Please see the data below: >> >> Benchmark Mode Cnt Unit >> SIZE Before After Gain >> GatherOperationsBenchmark.microByteGather128 thrpt 30 ops/ms >> 64 53682.012 52650.325 0.98 >> GatherOperationsBenchmark.microByteGather128 thrpt 30 ops/ms >> 256 14484.252 14255.156 0.98 >> GatherOperationsBenchmark.microByteGather128 thrpt 30 ops/ms >> 1024 3664.900 3595.615 0.98 >> GatherOperationsBenchmark.microByteGather128 thrpt 30 ops/ms >> 4096 908.31... > > Xiaohong Gong has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains three commits: > > - Address review comments > - Merge 'jdk:master' into JDK-8355563 > - 8355563: VectorAPI: Refactor current implementation of subword gather load > API Marked as reviewed by sviswanathan (Reviewer). Agree with Paul, these are minor regressions. Let us proceed with this patch. ------------- PR Review: https://git.openjdk.org/jdk/pull/25138#pullrequestreview-2977019367 PR Comment: https://git.openjdk.org/jdk/pull/25138#issuecomment-3025596784
