[LoopUtils,LV] Propagate fast-math flags on generated FCmp instructions

We're currently losing any fast-math flags when synthesizing fcmps for
min/max reductions. In LV, make sure we copy over the scalar inst's
flags. In LoopUtils, we know we only ever match patterns with
hasUnsafeAlgebra, so apply that to any synthesized ops.

llvm-svn: 248201

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -594,6 +594,13 @@ Value *RecurrenceDescriptor::createMinMaxOp(IRBuilder<> &Builder,
     break;
   }
 
+  // We only match FP sequences with unsafe algebra, so we can unconditionally
+  // set it on any generated instructions.
+  IRBuilder<>::FastMathFlagGuard FMFG(Builder);
+  FastMathFlags FMF;
+  FMF.setUnsafeAlgebra();
+  Builder.SetFastMathFlags(FMF);
+
   Value *Cmp;
   if (RK == MRK_FloatMin || RK == MRK_FloatMax)
     Cmp = Builder.CreateFCmp(P, Left, Right, "rdx.minmax.cmp");