[DAGCombiner] Leverage add's commutativity

Summary: This avoid the need to duplicate all pattern and actually end up exposing some opportunity to optimize existing pattern that did not exists in both directions on an existing test case.

Reviewers: mkuper, spatel, bkramer, RKSimon, zvi

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29541

llvm-svn: 294125

1 files changed, 14 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index aad07d8ae3c..8028eb3567e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -232,6 +232,7 @@ namespace {
     SDValue visitTokenFactor(SDNode *N);
     SDValue visitMERGE_VALUES(SDNode *N);
     SDValue visitADD(SDNode *N);
+    SDValue visitADDLike(SDValue N0, SDValue N1, SDNode *LocReference);
     SDValue visitSUB(SDNode *N);
     SDValue visitADDC(SDNode *N);
     SDValue visitSUBC(SDNode *N);
@@ -1782,6 +1783,19 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
       VT.isInteger() && DAG.haveNoCommonBitsSet(N0, N1))
     return DAG.getNode(ISD::OR, DL, VT, N0, N1);
 
+  if (SDValue Combined = visitADDLike(N0, N1, N))
+    return Combined;
+
+  if (SDValue Combined = visitADDLike(N1, N0, N))
+    return Combined;
+
+  return SDValue();
+}
+
+SDValue DAGCombiner::visitADDLike(SDValue N0, SDValue N1, SDNode *LocReference) {
+  EVT VT = N0.getValueType();
+  SDLoc DL(LocReference);
+
   // fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n))
   if (N1.getOpcode() == ISD::SHL && N1.getOperand(0).getOpcode() == ISD::SUB &&
       isNullConstantOrNullSplatConstant(N1.getOperand(0).getOperand(0)))
@@ -1789,12 +1803,6 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
                        DAG.getNode(ISD::SHL, DL, VT,
                                    N1.getOperand(0).getOperand(1),
                                    N1.getOperand(1)));
-  if (N0.getOpcode() == ISD::SHL && N0.getOperand(0).getOpcode() == ISD::SUB &&
-      isNullConstantOrNullSplatConstant(N0.getOperand(0).getOperand(0)))
-    return DAG.getNode(ISD::SUB, DL, VT, N1,
-                       DAG.getNode(ISD::SHL, DL, VT,
-                                   N0.getOperand(0).getOperand(1),
-                                   N0.getOperand(1)));
 
   if (N1.getOpcode() == ISD::AND) {
     SDValue AndOp0 = N1.getOperand(0);