[llvm] SelectionDAG: Support nofpclass (PR #108350)

[Jay Foad via llvm-commits]

================
@@ -11773,6 +11773,14 @@ void SelectionDAGISel::LowerArguments(const Function &F) {
           AssertOp = ISD::AssertSext;
         else if (Arg.hasAttribute(Attribute::ZExt))
           AssertOp = ISD::AssertZext;
+        if (Arg.hasAttribute(Attribute::NoFPClass)) {
+          SDNodeFlags InValFlags = InVals[i]->getFlags();
+          InValFlags.setNonNeg(Arg.getNoFPClass() & llvm::fcNegative);
+          InValFlags.setNoNaNs(Arg.getNoFPClass() & llvm::fcNan);
+          InValFlags.setNoInfs(Arg.getNoFPClass() & llvm::fcInf);
+          InValFlags.setNoSignedZeros(Arg.getNoFPClass() & llvm::fcNegZero);
----------------
jayfoad wrote:

This looks weird. What exactly does the `NoSignedZeros` flag mean on an InVal? Surely it does not just mean "the value is known not to be -0.0"?

https://github.com/llvm/llvm-project/pull/108350