[all-commits] [llvm/llvm-project] 891a2c: [AArch64] Change IssueWidth to 6 in AArch64SchedNe...

[David Sherwood via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 891a2c3c3411b9845dc869735f5428ea5d5fb304
      https://github.com/llvm/llvm-project/commit/891a2c3c3411b9845dc869735f5428ea5d5fb304
  Author: David Sherwood <david.sherwood at arm.com>
  Date:   2025-06-09 (Mon, 09 Jun 2025)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64SchedNeoverseV2.td
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-basic-instructions.s
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-clear-upper-regs.s
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-forwarding.s
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-sve-instructions.s
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-writeback.s
    M llvm/test/tools/llvm-mca/AArch64/Neoverse/V2-zero-lat-movs.s

  Log Message:
  -----------
  [AArch64] Change IssueWidth to 6 in AArch64SchedNeoverseV2.td (#142565)

I think that the issue width for neoverse-v2 CPUs is set too
high and does not properly reflect the dispatch constraints.
I tested various values of IssueWidth (16, 8 and 6) with runs
of SPEC2017 on a neoverse-v2 machine and I got the highest
overall geomean score with an issue width of 6, although it's
only a marginal 0.14% improvement. I also observed a 1-2%
improvement when testing the Gromacs application with some
workloads. Here are some notable changes in SPEC2017 ref
runtimes, i.e. has a ~0.5% change or greater ('-' means
faster):

548.exchange2: -1.7%
510.parest: -0.78%
538.imagick: -0.73%
500.perlbench: -0.57%
525.x264: -0.55%
507.cactuBSSN: -0.5%
520.omnetpp: -0.48%
511.povray: +0.57%
544.nab: +0.65%
503.bwaves: +0.68%
526.blender: +0.75%

If this patch causes any major regressions post-commit it can
be easily reverted, but I think it should be an overall
improvement.



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