Teach DAG combiner to commute commutable binary nodes in order to achieve sdisel CSE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48673 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 579870e6d0..9feefb9e30 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -758,6 +758,23 @@ SDOperand DAGCombiner::combine(SDNode *N) {
     }
   }
 
+  // If N is a commutative binary node, try commuting it to enable more 
+  // sdisel CSE.
+  if (RV.Val == 0 && 
+      SelectionDAG::isCommutativeBinOp(N->getOpcode()) &&
+      N->getNumValues() == 1) {
+    SDOperand N0 = N->getOperand(0);
+    SDOperand N1 = N->getOperand(1);
+    // Constant operands are canonicalized to RHS.
+    if (isa<ConstantSDNode>(N0) || !isa<ConstantSDNode>(N1)) {
+      SDOperand Ops[] = { N1, N0 };
+      SDNode *CSENode = DAG.getNodeIfExists(N->getOpcode(), N->getVTList(),
+                                            Ops, 2);
+      if (CSENode && CSENode->use_size() <= N->use_size())
+        return SDOperand(CSENode, 0);
+    }
+  }
+
   return RV;
 }