[llvm] [SDAG] Reverse the canonicalization of isInf/isNanOrInf (PR #81404)

[Matt Arsenault via llvm-commits]

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@@ -3467,12 +3467,50 @@ void SelectionDAGBuilder::visitICmp(const User &I) {
   setValue(&I, DAG.getSetCC(getCurSDLoc(), DestVT, Op1, Op2, Opcode));
 }
 
+SDValue SelectionDAGBuilder::lowerIsFpClass(Value *ClassVal,
+                                            FPClassTest ClassTest) {
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  const DataLayout &DL = DAG.getDataLayout();
+  SDLoc sdl = getCurSDLoc();
+
+  EVT DestVT =
+      TLI.getValueType(DL, CmpInst::makeCmpResultType(ClassVal->getType()));
+  EVT ArgVT = TLI.getValueType(DL, ClassVal->getType());
+  MachineFunction &MF = DAG.getMachineFunction();
+  const Function &F = MF.getFunction();
+  SDValue Op = getValue(ClassVal);
+  SDNodeFlags Flags;
+  Flags.setNoFPExcept(!F.getAttributes().hasFnAttr(llvm::Attribute::StrictFP));
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arsenm wrote:

this can just be true, is.fpclass can never raise exceptions (don't even need the flag?)

https://github.com/llvm/llvm-project/pull/81404