[DAGCombiner] Fold X - (-Y *Z) -> X + (Y * Z)

llvm-svn: 337518

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8ec1a3ed9fc..9a43aa69fec 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2629,6 +2629,24 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
     return DAG.getNode(ISD::SUB, DL, VT, N0.getOperand(0),
                        N0.getOperand(1).getOperand(0));
 
+  // fold (X - (-Y * Z)) -> (X + (Y * Z))
+  if (N1.getOpcode() == ISD::MUL && N1.hasOneUse()) {
+    if (N1.getOperand(0).getOpcode() == ISD::SUB &&
+        isNullConstantOrNullSplatConstant(N1.getOperand(0).getOperand(0))) {
+      SDValue Mul = DAG.getNode(ISD::MUL, DL, VT,
+                                N1.getOperand(0).getOperand(1),
+                                N1.getOperand(1));
+      return DAG.getNode(ISD::ADD, DL, VT, N0, Mul);
+    }
+    if (N1.getOperand(1).getOpcode() == ISD::SUB &&
+        isNullConstantOrNullSplatConstant(N1.getOperand(1).getOperand(0))) {
+      SDValue Mul = DAG.getNode(ISD::MUL, DL, VT,
+                                N1.getOperand(0),
+                                N1.getOperand(1).getOperand(1));
+      return DAG.getNode(ISD::ADD, DL, VT, N0, Mul);
+    }
+  }
+
   // If either operand of a sub is undef, the result is undef
   if (N0.isUndef())
     return N0;