[llvm] [ValueTracking][KnownFPClass] Cover known no-infinity cases for powi (PR #191736)

[Tim Gymnich via llvm-commits]

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@@ -880,6 +879,39 @@ KnownFPClass KnownFPClass::powi(const KnownFPClass &KnownSrc,
     return Known;
   }
 
+  // powi(x, exp) --> inf
+  // when:
+  //   * powi(inf, exp), exp > 0
+  //   * powi(+/-0, exp), exp < 0
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tgymnich wrote:

Sorry, I thought we were trying to show its never inf. I would rather use `Known.isKnownAlways(fcInf)` in the cases where we know its inf.
`

https://github.com/llvm/llvm-project/pull/191736