[all-commits] [llvm/llvm-project] e508d6: [X86][AVX] Fold extract_subvector(broadcast(x), c) ...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: e508d643cfd583b92dfd5484e27fb280cf0f3c60
      https://github.com/llvm/llvm-project/commit/e508d643cfd583b92dfd5484e27fb280cf0f3c60
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2020-05-24 (Sun, 24 May 2020)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/pr45443.ll
    M llvm/test/CodeGen/X86/vector-fshl-rot-256.ll
    M llvm/test/CodeGen/X86/vector-fshl-rot-512.ll
    M llvm/test/CodeGen/X86/vector-fshr-rot-512.ll
    M llvm/test/CodeGen/X86/vector-rotate-256.ll
    M llvm/test/CodeGen/X86/vector-shift-ashr-256.ll
    M llvm/test/CodeGen/X86/vector-shift-lshr-256.ll
    M llvm/test/CodeGen/X86/vector-shift-shl-256.ll

  Log Message:
  -----------
  [X86][AVX] Fold extract_subvector(broadcast(x),c) -> extract_subvector(broadcast(x),0) iff c != 0

If we're extracting an upper subvector from a broadcast we're better off extracting the lowest subvector instead as it avoids an actual extract instruction and might help SimplifyDemandedVectorElts further simplify the code.