[all-commits] [llvm/llvm-project] 9bb1d0: [X86] getShuffleCost - when splitting shuffles, if...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9bb1d0369c064d50c5f0f7ed6313289c8a42d14f
      https://github.com/llvm/llvm-project/commit/9bb1d0369c064d50c5f0f7ed6313289c8a42d14f
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2024-12-19 (Thu, 19 Dec 2024)

  Changed paths:
    M llvm/lib/Target/X86/X86TargetTransformInfo.cpp
    M llvm/test/Analysis/CostModel/X86/reduction.ll

  Log Message:
  -----------
  [X86] getShuffleCost - when splitting shuffles, if a whole vector source is just copied we should treat this as free. (#120561)

If the shuffle split results in referencing a single legalised whole vector (i.e. no permutation), then this can be treated as free.

We already do something similar for broadcasts / whole subvector insertion + extraction - its purely an issue for register allocation.



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