[llvm] [InstCombine] Resolve incorrect submasking in foldIntrinsicIsFPClass (PR #190504)

[Yingwei Zheng via llvm-commits]

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@@ -863,6 +863,37 @@ define i1 @test_class_is_not_nan_nnan_src_strict(float %x) strictfp {
   ret i1 %class
 }
 
+; Fold to true when known classes are a strict subset of the mask
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dtcxzyw wrote:

All the cases you added are already handled by InstCombine: https://godbolt.org/z/WhbP9K4xP

I guess it has been covered by the optimization above: `(Mask & Known.KnownFPClasses) == Mask` means `Mask` is a subset of `Known.KnownFPClasses`. In this context, `(Known.KnownFPClasses & ~Mask) == fcNone` is equivalent to `Mask == Known.KnownFPClasses`.


https://github.com/llvm/llvm-project/pull/190504