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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334753 91177308-0d34-0410-b5e6-96231b3b80d8

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,

test/CodeGen/X86/fp-fold.ll

@@ -62,6 +62,17 @@ define float @fsub_self(float %x) {
   ret float %r
 }
 
+define float @fsub_neg_x_y(float %x, float %y) {
+; ANY-LABEL: fsub_neg_x_y:
+; ANY:       # %bb.0:
+; ANY-NEXT:    subss %xmm0, %xmm1
+; ANY-NEXT:    movaps %xmm1, %xmm0
+; ANY-NEXT:    retq
+  %neg = fsub nsz float 0.0, %x
+  %r = fadd nsz float %neg, %y
+  ret float %r
+}
+
 define float @fsub_negzero(float %x) {
 ; STRICT-LABEL: fsub_negzero:
 ; STRICT:       # %bb.0: