[PATCH] D59961: [DAGCombiner] simplify shuffle of shuffle

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon accepted this revision.
RKSimon added a comment.
This revision is now accepted and ready to land.

LGTM



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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:17952
+  ArrayRef<int> Mask0 = Shuf0->getMask();
+  for (int i = 0, e = (int)(Shuf->getMask().size()); i != e; ++i) {
+    // Ignore undef elements.
----------------
e = Mask.size()?


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:17956
+      continue;
+    // Is the element of the shuffle operand chosen by this shuffle the same as
+    // the element chosen by the shuffle operand itself?
----------------
Maybe assert that 0 <= Mask[i] && Mask[i] < e ?


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:17963
+  // shuffle, so we can replace this value.
+  return SDValue(Shuf0, 0);
+}
----------------
Just return Shuf->getOperand(0) ?


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  https://reviews.llvm.org/D59961/new/

https://reviews.llvm.org/D59961