On Fri, 19 Apr 2024 16:25:28 GMT, Scott Gibbons <sgibb...@openjdk.org> wrote:
>> This code makes an intrinsic stub for `Unsafe::setMemory` for x86_64. See >> [this PR](https://github.com/openjdk/jdk/pull/16760) for discussion around >> this change. >> >> Overall, making this an intrinsic improves overall performance of >> `Unsafe::setMemory` by up to 4x for all buffer sizes. >> >> Tested with tier-1 (and full CI). I've added a table of the before and >> after numbers for the JMH I ran (`MemorySegmentZeroUnsafe`). >> >> [setMemoryBM.txt](https://github.com/openjdk/jdk/files/14808974/setMemoryBM.txt) > > Scott Gibbons has updated the pull request incrementally with one additional > commit since the last revision: > > Address review comments; update copyright years I'm not really qualified as a compiler code reviewer, but I've left some comments to try and help this along. src/hotspot/cpu/x86/stubGenerator_x86_64_arraycopy.cpp line 2523: > 2521: // Number of (8*X)-byte chunks into rScratch1 > 2522: __ movq(tmp, size); > 2523: __ shrq(tmp, 3); `shr` [sets the zero flag][1], so I think you can just move the jump to after the shift and avoid a separate comparison? ```suggestion // Number of (8*X)-byte chunks into rScratch1 __ movq(tmp, size); __ shrq(tmp, 3); __ jccb(Assembler::zero, L_Tail); [1]: https://www.felixcloutier.com/x86/sal:sar:shl:shr#flags-affected ------------- PR Review: https://git.openjdk.org/jdk/pull/18555#pullrequestreview-2011751831 PR Review Comment: https://git.openjdk.org/jdk/pull/18555#discussion_r1572712233
