[DAGCombine] Use FoldConstantArithmetic() to perform C2-(A+C1) -> (C2…

…-C1)-A fold

Summary:
No tests change, and i'm not sure how to test this, but it's better safe than sorry.

Reviewers: spatel, RKSimon, craig.topper, t.p.northover

Reviewed By: craig.topper

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62663

llvm-svn: 362132

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -2868,7 +2868,9 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
     SDValue N11 = N1.getOperand(1);
     if (isConstantOrConstantVector(N0, /* NoOpaques */ true) &&
         isConstantOrConstantVector(N11, /* NoOpaques */ true)) {
-      SDValue NewC = DAG.getNode(ISD::SUB, DL, VT, N0, N11);
+      SDValue NewC = DAG.FoldConstantArithmetic(ISD::SUB, DL, VT, N0.getNode(),
+                                                N11.getNode());
+      assert(NewC && "Constant folding failed");
       return DAG.getNode(ISD::SUB, DL, VT, NewC, N1.getOperand(0));
     }
   }