extend folding fsub/fadd to fneg for FMF

Summary: This change provides a common optimization path for both Unsafe and FMF driven optimization for this fsub fold adding reassociation, as it the flag that most closely represents the translation

Reviewers: spatel, wristow, arsenm

Reviewed By: spatel

Subscribers: wdng

Differential Revision: https://reviews.llvm.org/D50195

llvm-svn: 339357

1 files changed, 10 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f78688787dd..5bf0e1635a6 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10935,20 +10935,22 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
     }
   }
 
-  // fold (fsub A, (fneg B)) -> (fadd A, B)
-  if (isNegatibleForFree(N1, LegalOperations, TLI, &Options))
-    return DAG.getNode(ISD::FADD, DL, VT, N0,
-                       GetNegatedExpression(N1, DAG, LegalOperations), Flags);
-
-  if (Options.UnsafeFPMath && N1.getOpcode() == ISD::FADD) {
+  if ((Options.UnsafeFPMath ||
+      (Flags.hasAllowReassociation() && Flags.hasNoSignedZeros()))
+      && N1.getOpcode() == ISD::FADD) {
     // X - (X + Y) -> -Y
     if (N0 == N1->getOperand(0))
-      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(1));
+      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(1), Flags);
     // X - (Y + X) -> -Y
     if (N0 == N1->getOperand(1))
-      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(0));
+      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(0), Flags);
   }
 
+  // fold (fsub A, (fneg B)) -> (fadd A, B)
+  if (isNegatibleForFree(N1, LegalOperations, TLI, &Options))
+    return DAG.getNode(ISD::FADD, DL, VT, N0,
+                       GetNegatedExpression(N1, DAG, LegalOperations), Flags);
+
   // FSUB -> FMA combines:
   if (SDValue Fused = visitFSUBForFMACombine(N)) {
     AddToWorklist(Fused.getNode());