[all-commits] [llvm/llvm-project] 71f342: [X86][AVX] Fold PACK(LOSUBVECTOR(SHUFFLE(X)), HISUB...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 71f342d6c3d82fa45c180f1981710bb6092d39fc
      https://github.com/llvm/llvm-project/commit/71f342d6c3d82fa45c180f1981710bb6092d39fc
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2020-07-04 (Sat, 04 Jul 2020)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/bitcast-setcc-512.ll
    M llvm/test/CodeGen/X86/bitcast-vector-bool.ll
    M llvm/test/CodeGen/X86/masked_expandload.ll
    M llvm/test/CodeGen/X86/masked_store_trunc.ll
    M llvm/test/CodeGen/X86/masked_store_trunc_ssat.ll
    M llvm/test/CodeGen/X86/masked_store_trunc_usat.ll
    M llvm/test/CodeGen/X86/movmsk-cmp.ll
    M llvm/test/CodeGen/X86/psubus.ll
    M llvm/test/CodeGen/X86/vector-compare-results.ll
    M llvm/test/CodeGen/X86/vector-reduce-and-bool.ll
    M llvm/test/CodeGen/X86/vector-reduce-or-bool.ll
    M llvm/test/CodeGen/X86/vector-reduce-xor-bool.ll
    M llvm/test/CodeGen/X86/vector-trunc-packus.ll
    M llvm/test/CodeGen/X86/vector-trunc-ssat.ll
    M llvm/test/CodeGen/X86/vector-trunc-usat.ll
    M llvm/test/CodeGen/X86/vector-trunc.ll
    M llvm/test/CodeGen/X86/vselect-packss.ll

  Log Message:
  -----------
  [X86][AVX] Fold PACK(LOSUBVECTOR(SHUFFLE(X)),HISUBVECTOR(SHUFFLE(X))) -> SHUFFLE(PACK(LOSUBVECTOR(X),HISUBVECTOR(X)))

Using PACK for truncations leaves us with intermediate shuffles that can be tricky to remove while the truncation tree is being formed.

This fold helps pull out the PERMQ case which is one of the most common, avoiding some costly lane-crossing shuffles.

A future patch will begin adding more general shuffle folding, which we should be able to use for HADD/HSUB as well.