Add a canonicalization that got lost, fixing PowerPC/fold-li.ll:SUB

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23693 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index efeee071f0be22c25c7b44824e1a8e414f45ea1f..0098a56a9a241f67b03555c4f7206b7748aff382 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -517,9 +517,11 @@ SDOperand DAGCombiner::visitSUB(SDNode *N) {
   if (N0C && N1C)
     return DAG.getConstant(N0C->getValue() - N1C->getValue(),
                            N->getValueType(0));
-  // fold (sub x, 0) -> x
-  if (N1C && N1C->isNullValue())
-    return N0;
+  // fold (sub x, c) -> (add x, -c)
+  if (N1C)
+    return DAG.getNode(ISD::ADD, N0.getValueType(), N0,
+                       DAG.getConstant(-N1C->getValue(), N0.getValueType()));
+
   // fold (A+B)-A -> B
   if (N0.getOpcode() == ISD::ADD && N0.getOperand(0) == N1)
     return N0.getOperand(1);