[DAGCombine] Fix for PR35761

I had falsely assumed that constant operands would be operand(1) of
the bin ops that may need their constant operand to be masked.

Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=35761

Differential Revision: https://reviews.llvm.org/D41667

llvm-svn: 321991

1 files changed, 10 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 1fcb010eac5..d823c455b5e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3923,10 +3923,16 @@ bool DAGCombiner::BackwardsPropagateMask(SDNode *N, SelectionDAG &DAG) {
 
     // Narrow any constants that need it.
     for (auto *LogicN : NodesWithConsts) {
-      auto *C = cast<ConstantSDNode>(LogicN->getOperand(1));
-      SDValue And = DAG.getNode(ISD::AND, SDLoc(C), C->getValueType(0),
-                                SDValue(C, 0), MaskOp);
-      DAG.UpdateNodeOperands(LogicN, LogicN->getOperand(0), And);
+      SDValue Op0 = LogicN->getOperand(0);
+      SDValue Op1 = LogicN->getOperand(1);
+
+      if (isa<ConstantSDNode>(Op0))
+          std::swap(Op0, Op1);
+
+      SDValue And = DAG.getNode(ISD::AND, SDLoc(Op1), Op1.getValueType(),
+                                Op1, MaskOp);
+
+      DAG.UpdateNodeOperands(LogicN, Op0, And);
     }
 
     // Create narrow loads.