[PATCH] D137811: InstCombine: Perform basic isnan combines on llvm.is.fpclass

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D137811#4065720 <https://reviews.llvm.org/D137811#4065720>, @arsenm wrote:

>> But they have different behavior if `x` is signaling NaN. Although the replacement is proposed for strictfp functions only, inlining may require conversion to a form that uses constrained intrinsics. The resulting code would have different behavior than original.
>
> A transformation that’s valid for !strictfp functions cannot be invalid because of the potential for being inlined into a strictfp function. If this isn’t possible, there is a representational issue the inliner would need to account for.

Thinking about this more, I think any situation where this could be an issue would be malformed to begin with. You had a piece of code that was expecting exceptions to be enabled calling into code where exceptions were disabled without turning exceptions off


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