[PATCH] D25691: [DAGCombiner] Add vector demanded elements support to computeKnownBits

Eli Friedman via llvm-commits llvm-commits at lists.llvm.org
Tue Oct 18 11:24:27 PDT 2016

efriedma added inline comments.

Comment at: lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2555
+      unsigned Idx = ConstEltNo->getZExtValue();
+      assert(Idx < NumSrcElts && "Out of range vector element index");
+      APInt DemandedElt = APInt::getOneBitSet(NumSrcElts, Idx);
Are your sure it isn't possible to trigger this assertion?  I think DAGCombine will delete an extractelement with an out-of-range index, but you can't depend on that happening before this code runs.



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