[PATCH] D66718: [DAGCombiner] (insert_vector_elt (vector_shuffle X, Y), (extract_vector_elt X, N), IdxC) -> (vector_shuffle X, Y)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:16456
+
+      return DAG.getVectorShuffle(Vec.getValueType(), SDLoc(N),
+                                  Vec.getOperand(0), Vec.getOperand(1),
----------------
deadalnix wrote:
> RKSimon wrote:
> > You need to check NewMask is legal: if (!TLI.isShuffleMaskLegal(NewMask, Vec.getValueType()))
> There are a few places where isShuffleMaskLegal is used. Some try to flip operands inc ase it isn't legal. Should that be an idiom?
I've no objection to you creating a static helper that tries isShuffleMaskLegal with original and commuted masks, and call DAG.getVectorShuffle on success.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D66718/new/

https://reviews.llvm.org/D66718