Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4442,7 +4442,7 @@
   case ISD::FMUL:
   case ISD::FDIV:
   case ISD::FREM:
-    if (getTarget().Options.UnsafeFPMath) {
+    if (getTarget().Options.UnsafeFPMath || Flags.isFast()) {
       if (Opcode == ISD::FADD) {
         // x+0 --> x
         if (N2CFP && N2CFP->getValueAPF().isZero())
Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2769,6 +2769,10 @@
     Flags.setVectorReduction(true);
     LLVM_DEBUG(dbgs() << "Detected a reduction operation:" << I << "\n");
   }
+  // need Flags for Selection DAG decisions here
+  if (auto *FPMO = dyn_cast<FPMathOperator>(&I)) {
+    Flags.copyFMF(*FPMO);
+  }
 
   SDValue Op1 = getValue(I.getOperand(0));
   SDValue Op2 = getValue(I.getOperand(1));