[all-commits] [llvm/llvm-project] 19d028: [X86][AVX] Fold extract_subvector(VSRLI/VSHLI(x, 32...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 19d02842ee56089b9208875ce4582e113e08fb6d
      https://github.com/llvm/llvm-project/commit/19d02842ee56089b9208875ce4582e113e08fb6d
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2021-01-20 (Wed, 20 Jan 2021)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/combine-sra.ll
    M llvm/test/CodeGen/X86/pmul.ll
    M llvm/test/CodeGen/X86/vec-strict-inttofp-256.ll

  Log Message:
  -----------
  [X86][AVX] Fold extract_subvector(VSRLI/VSHLI(x,32)) -> VSRLI/VSHLI(extract_subvector(x),32)

As discussed on D56387, if we're shifting to extract the upper/lower half of a vXi64 vector then we're actually better off performing this at the subvector level as its very likely to fold into something.

combineConcatVectorOps can perform this in reverse if necessary.