[all-commits] [llvm/llvm-project] 5626bd: [X86] Fix SLM scheduler model for PMULLD (PR37059)

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5626bd428930aa2cb2b5fdd69e93620e0d2b0532
      https://github.com/llvm/llvm-project/commit/5626bd428930aa2cb2b5fdd69e93620e0d2b0532
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2022-04-08 (Fri, 08 Apr 2022)

  Changed paths:
    M llvm/lib/Target/X86/X86ScheduleSLM.td
    M llvm/test/CodeGen/X86/slow-pmulld.ll
    M llvm/test/tools/llvm-mca/X86/SLM/resources-sse41.s

  Log Message:
  -----------
  [X86] Fix SLM scheduler model for PMULLD (PR37059)

Adjust the PMULLD entry to match the Intel AoM numbers - PMULLD is a uop nightmare on SLM and we should model it as such.

We had reports of internal regressions the last time this was attempted (rG13a0f83a05ff), but no public repros, and tests I did last year when I had access to a SLM box failed to see anything. My hunch is that the more aggressive PMULLD -> PMADDWD folds we now perform might have helped. We can revisit this again if we ever receive an actual repro.

Fixes #36407