[PATCH] D66504: [X86][DAGCombiner] Teach narrowShuffle to use concat_vectors instead of inserting into undef

[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 with one optional change



================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:19482
+  auto ConcatWithUndef = [](SDValue Concat) {
+    return std::all_of(std::next(Concat->op_begin()), Concat->op_end(),
+                       [](const SDValue &Op) {
----------------
RKSimon wrote:
> Not sure if its worth it but you could put the check for getOpcode() == ISD::CONCAT_VECTORS in here as well.
I meant
```
return Concat.getOpcode() == ISD::CONCAT_VECTORS && std::all_of();
```


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  https://reviews.llvm.org/D66504/new/

https://reviews.llvm.org/D66504