[all-commits] [llvm/llvm-project] 3529cc: DAG: Avoid breaking legal vector_shuffle with mult...

[Matt Arsenault via All-commits]

  Branch: refs/heads/users/arsenm/dag/avoid-breaking-multi-use-legal-shuffle-after-legalize
  Home:   https://github.com/llvm/llvm-project
  Commit: 3529cc43a3f23499586e22d9ada2730288115f6a
      https://github.com/llvm/llvm-project/commit/3529cc43a3f23499586e22d9ada2730288115f6a
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2025-01-21 (Tue, 21 Jan 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4f32.v2f32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4f32.v3f32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4f32.v4f32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4i32.v2i32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4i32.v3i32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4i32.v4i32.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4p3.v2p3.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4p3.v3p3.ll
    M llvm/test/CodeGen/AMDGPU/shufflevector.v4p3.v4p3.ll

  Log Message:
  -----------
  DAG: Avoid breaking legal vector_shuffle with multiple uses

Previously this combine would undo AMDGPU's new custom legalization of
wide vector shuffles into 2 element pieces. The comment also
states that this combine is only done before legalization,
but the case with a build_vector source was unconditional.

We probably don't want to do this if the multiple uses are full
scalarization of the vector, but this seems to work well enough.
Scalarizing extracts should have folded out pre-legalize.



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