[llvm] r339561 - [DAGCombiner] simplifyDivRem - add comment describing divide by undef/zero combine. NFC.

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Mon Aug 13 06:12:25 2018
New Revision: 339561

URL: http://llvm.org/viewvc/llvm-project?rev=339561&view=rev
Log:
[DAGCombiner] simplifyDivRem - add comment describing divide by undef/zero combine. NFC.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=339561&r1=339560&r2=339561&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Aug 13 06:12:25 2018
@@ -3076,6 +3076,11 @@ static SDValue simplifyDivRem(SDNode *N,
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
 
+  // X / undef -> undef
+  // X % undef -> undef
+  // X / 0 -> undef
+  // X % 0 -> undef
+  // NOTE: This includes vectors where any divisor element is zero/undef.
   if (DAG.isUndef(N->getOpcode(), {N0, N1}))
     return DAG.getUNDEF(VT);