[SelectionDAG] Remove UnsafeFPMath check in visitFADDForFMACombine

Author: paperchalice

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -16619,8 +16619,8 @@ SDValue DAGCombiner::visitFADDForFMACombine(SDNode *N) {
   if (!HasFMAD && !HasFMA)
     return SDValue();
 
-  bool AllowFusionGlobally = (Options.AllowFPOpFusion == FPOpFusion::Fast ||
-                              Options.UnsafeFPMath || HasFMAD);
+  bool AllowFusionGlobally =
+      Options.AllowFPOpFusion == FPOpFusion::Fast || HasFMAD;
   // If the addition is not contractable, do not combine.
   if (!AllowFusionGlobally && !N->getFlags().hasAllowContract())
     return SDValue();
@@ -17826,6 +17826,7 @@ template <class MatchContextClass> SDValue DAGCombiner::visitFMA(SDNode *N) {
   SDValue N2 = N->getOperand(2);
   ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
   ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1);
+  ConstantFPSDNode *N2CFP = dyn_cast<ConstantFPSDNode>(N2);
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
   const TargetOptions &Options = DAG.getTarget().Options;
@@ -17855,12 +17856,26 @@ template <class MatchContextClass> SDValue DAGCombiner::visitFMA(SDNode *N) {
   }
 
   // FIXME: use fast math flags instead of Options.UnsafeFPMath
-  if (Options.UnsafeFPMath) {
+  // TODO: Finally migrate away from global TargetOptions.
+  if (Options.AllowFPOpFusion == FPOpFusion::Fast ||
+      Options.NoSignedZerosFPMath || N->getFlags().hasNoSignedZeros()) {
     if (N0CFP && N0CFP->isZero())
       return N2;
     if (N1CFP && N1CFP->isZero())
       return N2;
   }
+  // Handle (fma x, 0.0, c) and (fma 0.0, x, c)
+  if (Options.AllowFPOpFusion == FPOpFusion::Fast ||
+      (Options.NoInfsFPMath && Options.NoNaNsFPMath) ||
+      (N->getFlags().hasNoInfs() && N->getFlags().hasNoNaNs())) {
+    // Fold to c only when c is not -0.0.
+    if (N2CFP && !N2CFP->isExactlyValue(-0.0)) {
+      if (N0CFP && N0CFP->isZero())
+        return N2;
+      if (N1CFP && N1CFP->isZero())
+        return N2;
+    }
+  }
 
   // FIXME: Support splat of constant.
   if (N0CFP && N0CFP->isExactlyValue(1.0))

llvm/test/CodeGen/AArch64/arm64-fp-contract-zero.ll

@@ -1,18 +1,16 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=arm64 -fp-contract=fast -o - %s | FileCheck %s
+; RUN: llc -mtriple=arm64 -o - %s | FileCheck %s
 
 
 ; Make sure we don't try to fold an fneg into +0.0, creating an illegal constant
 ; -0.0. It's also good, though not essential, that we don't resort to a litpool.
 define double @test_fms_fold(double %a, double %b) {
 ; CHECK-LABEL: test_fms_fold:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    movi d2, #0000000000000000
-; CHECK-NEXT:    fmul d1, d1, d2
-; CHECK-NEXT:    fnmsub d0, d0, d2, d1
+; CHECK-NEXT:    movi {{d[0-9]+}}, #0000000000000000
 ; CHECK-NEXT:    ret
-  %mul = fmul double %a, 0.000000e+00
-  %mul1 = fmul double %b, 0.000000e+00
+  %mul = fmul fast double %a, 0.000000e+00
+  %mul1 = fmul fast double %b, 0.000000e+00
   %sub = fsub double %mul, %mul1
   ret double %sub
 }