[PATCH] D26605: [DAGCombiner] Fix infinite loop in vector mul/shl combining

[John Brawn via llvm-commits]

john.brawn added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/SelectionDAG.cpp:3476
+      continue;
+    }
     ConstantSDNode *V1 = dyn_cast<ConstantSDNode>(BV1->getOperand(I));
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RKSimon wrote:
> I don't think this is safe (e.g. OR(C1, UNDEF) --> at least C1).
Hmm, I'd thought that FoldConstantVectorArithmetic folds any undef input element into an undef output element, but looking more closely it calls getNode on each element pair and it's only for some operations that results in undef. I'll try making FoldConstantArithmetic do the same.


Repository:
  rL LLVM

https://reviews.llvm.org/D26605