[PATCH] D62661: [DAGCombine] Use FoldConstantArithmetic() to perform ((c1-A)+c2) -> (c1+c2)-A fold

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, RKSimon, craig.topper.
lebedev.ri added a project: LLVM.
lebedev.ri added a child revision: D62662: [DAGCombine] ((A-c1)+c2) -> (A+(c2-c1))  constant-fold.

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


Repository:
  rL LLVM

https://reviews.llvm.org/D62661

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp


Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2164,10 +2164,10 @@
     // fold ((c1-A)+c2) -> (c1+c2)-A
     if (N0.getOpcode() == ISD::SUB &&
         isConstantOrConstantVector(N0.getOperand(0), /* NoOpaque */ true)) {
-      // FIXME: Adding 2 constants should be handled by FoldConstantArithmetic.
-      return DAG.getNode(ISD::SUB, DL, VT,
-                         DAG.getNode(ISD::ADD, DL, VT, N1, N0.getOperand(0)),
-                         N0.getOperand(1));
+      SDValue Add = DAG.FoldConstantArithmetic(ISD::ADD, DL, VT, N1.getNode(),
+                                               N0.getOperand(0).getNode());
+      assert(Add && "Constant folding failed");
+      return DAG.getNode(ISD::SUB, DL, VT, Add, N0.getOperand(1));
     }
 
     // add (sext i1 X), 1 -> zext (not i1 X)


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