[llvm] [ValueTracking] Fix computeKnownFPClass for fpext (PR #81972)

[Nikita Popov via llvm-commits]

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@@ -142,7 +142,7 @@ define double @ret_fpext_f32_to_f64_nosub(float nofpclass(sub) %arg0) {
 }
 
 define double @ret_fpext_f32_to_f64_nonorm(float nofpclass(norm) %arg0) {
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nikic wrote:

It's unfortunate that nofpclass is tested via Attributor, which means it can't be verified with alive.

https://github.com/llvm/llvm-project/pull/81972