[all-commits] [llvm/llvm-project] 5dbe5d: [DAG] Commute shuffle(splat(A, u), shuffle(C, D)) ->...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 5dbe5d2c91209db9830d5b17093c408f22a7b471
      https://github.com/llvm/llvm-project/commit/5dbe5d2c91209db9830d5b17093c408f22a7b471
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2021-01-22 (Fri, 22 Jan 2021)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/X86/haddsub-undef.ll

  Log Message:
  -----------
  [DAG] Commute shuffle(splat(A,u), shuffle(C,D)) -> shuffle'(shuffle(C,D), splat(A,u))

We only merge shuffles if the inner (LHS) shuffle is a non-splat, so commute these shuffles to improve merging of multiple shuffles.