updating isNegatibleForFree and GetNegatedExpression with fmf for fadd

Summary:  A FMF constraint is added to FADD with unsafe still available as the fallback

Reviewers: spatel, wristow, arsenm, hfinkel

Reviewed By: spatel

Subscribers: wdng

Differential Revision: https://reviews.llvm.org/D48180

llvm-svn: 334753

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ac324fe4c3d..33821c33bb7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -704,8 +704,8 @@ static char isNegatibleForFree(SDValue Op, bool LegalOperations,
       TLI.isFPImmLegal(neg(cast<ConstantFPSDNode>(Op)->getValueAPF()), VT);
   }
   case ISD::FADD:
-    // FIXME: determine better conditions for this xform.
-    if (!Options->UnsafeFPMath) return 0;
+    if (!Options->UnsafeFPMath && !Flags.hasNoSignedZeros())
+      return 0;
 
     // After operation legalization, it might not be legal to create new FSUBs.
     if (LegalOperations && !TLI.isOperationLegalOrCustom(ISD::FSUB, VT))
@@ -766,8 +766,7 @@ static SDValue GetNegatedExpression(SDValue Op, SelectionDAG &DAG,
     return DAG.getConstantFP(V, SDLoc(Op), Op.getValueType());
   }
   case ISD::FADD:
-    // FIXME: determine better conditions for this xform.
-    assert(Options.UnsafeFPMath);
+    assert(Options.UnsafeFPMath || Flags.hasNoSignedZeros());
 
     // fold (fneg (fadd A, B)) -> (fsub (fneg A), B)
     if (isNegatibleForFree(Op.getOperand(0), LegalOperations,