[PATCH] D62663: [DAGCombine] Use FoldConstantArithmetic() to perform C2-(A+C1) -> (C2-C1)-A fold

Roman Lebedev via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Thu May 30 07:14:18 PDT 2019

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, RKSimon, craig.topper.
lebedev.ri added a project: LLVM.
lebedev.ri added a parent 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.




Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2875,7 +2875,9 @@
     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));

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