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

2 files changed, 31 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 579870e..9feefb9 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;
 } 
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9331e8b..94eba83 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3291,6 +3291,20 @@ SDNode *SelectionDAG::getTargetNode(unsigned Opcode,
                  Ops, NumOps).Val;
 }
 
+/// getNodeIfExists - Get the specified node if it's already available, or
+/// else return NULL.
+SDNode *SelectionDAG::getNodeIfExists(unsigned Opcode, SDVTList VTList,
+                                      const SDOperand *Ops, unsigned NumOps) {
+  if (VTList.VTs[VTList.NumVTs-1] != MVT::Flag) {
+    FoldingSetNodeID ID;
+    AddNodeIDNode(ID, Opcode, VTList, Ops, NumOps);
+    void *IP = 0;
+    if (SDNode *E = CSEMap.FindNodeOrInsertPos(ID, IP))
+      return E;
+  }
+  return NULL;
+}
+
 
 /// ReplaceAllUsesWith - Modify anything using 'From' to use 'To' instead.
 /// This can cause recursive merging of nodes in the DAG.