allow SRL to simplify its operands, as it doesn't demand all bits as input.

llvm-svn: 36245

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 20b9a588e2e..88596d65db3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1728,7 +1728,7 @@ SDOperand DAGCombiner::visitSHL(SDNode *N) {
   // if (shl x, c) is known to be zero, return 0
   if (TLI.MaskedValueIsZero(SDOperand(N, 0), MVT::getIntVTBitMask(VT)))
     return DAG.getConstant(0, VT);
-  if (SimplifyDemandedBits(SDOperand(N, 0)))
+  if (N1C && SimplifyDemandedBits(SDOperand(N, 0)))
     return SDOperand(N, 0);
   // fold (shl (shl x, c1), c2) -> 0 or (shl x, c1+c2)
   if (N1C && N0.getOpcode() == ISD::SHL && 
@@ -1907,6 +1907,12 @@ SDOperand DAGCombiner::visitSRL(SDNode *N) {
       return DAG.getNode(ISD::XOR, VT, Op, DAG.getConstant(1, VT));
     }
   }
+  
+  // fold operands of srl based on knowledge that the low bits are not
+  // demanded.
+  if (N1C && SimplifyDemandedBits(SDOperand(N, 0)))
+    return SDOperand(N, 0);
+  
   return SDOperand();
 }