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

[Jay Foad via llvm-commits]

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@@ -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);
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jayfoad wrote:

> Yes, "the value is known not to be -0.0" is one case

I don't think that's true - unless you can point me at some evidence? (I am more familiar with how these flags are defined in IR and MIR than in SDNodes.) I think the NoSignedZeros flag only makes sense on certain _operations_ like FADD, not on arbitrary _values_.

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