[PATCH] D107068: [DAG] DAGCombiner::visitVECTOR_SHUFFLE - recognise INSERT_SUBVECTOR patterns.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:21308-21310
+      // Don't bother if we have a unary shuffle.
+      if (all_of(Mask, [NumElts](int M) { return M < (int)NumElts; }))
+        return SDValue();
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lebedev.ri wrote:
> +` Undef's are okay.`
> 
> I believe we can't have `-2` (zero) mask elements yet here?
Yeah - SelectionDAG::getVectorShuffle asserts: "M < (NElts * 2) && M >= -1;"

I'll add a comment making to clear undefs are ok


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  https://reviews.llvm.org/D107068/new/

https://reviews.llvm.org/D107068