[llvm] r310832 - [DAGCombine] Do not try to deduplicate commutative operations if both operand are the same.

[Amaury Sechet via llvm-commits]

Author: deadalnix
Date: Mon Aug 14 04:44:03 2017
New Revision: 310832

URL: http://llvm.org/viewvc/llvm-project?rev=310832&view=rev
Log:
[DAGCombine] Do not try to deduplicate commutative operations if both operand are the same.

Summary: It is creating useless work as the commuted nodes is the same as the node we are working on in that case.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33840

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=310832&r1=310831&r2=310832&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Aug 14 04:44:03 2017
@@ -1614,15 +1614,15 @@ SDValue DAGCombiner::combine(SDNode *N)
     }
   }
 
-  // If N is a commutative binary node, try commuting it to enable more
-  // sdisel CSE.
+  // If N is a commutative binary node, try eliminate it if the commuted
+  // version is already present in the DAG.
   if (!RV.getNode() && TLI.isCommutativeBinOp(N->getOpcode()) &&
       N->getNumValues() == 1) {
     SDValue N0 = N->getOperand(0);
     SDValue N1 = N->getOperand(1);
 
     // Constant operands are canonicalized to RHS.
-    if (isa<ConstantSDNode>(N0) || !isa<ConstantSDNode>(N1)) {
+    if (N0 != N1 && (isa<ConstantSDNode>(N0) || !isa<ConstantSDNode>(N1))) {
       SDValue Ops[] = {N1, N0};
       SDNode *CSENode = DAG.getNodeIfExists(N->getOpcode(), N->getVTList(), Ops,
                                             N->getFlags());