[llvm] [KnownFPClass] Refactor direct access to `KnownFPClass::SignBit` [NFC] (PR #218514)

[via llvm-commits]

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@@ -28,16 +28,21 @@ struct KnownFPClass {
   /// Floating-point classes the value could be one of.
   FPClassTest KnownFPClasses = fcAllFlags;
 
+  std::optional<bool> SignBitValue;
+
   /// std::nullopt if the sign bit is unknown, true if the sign bit is
   /// definitely set or false if the sign bit is definitely unset.
-  std::optional<bool> SignBit;
+  std::optional<bool> SignBit() const { return SignBitValue; }
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ZERICO2005 wrote:

renamed to `getSignBit()`

https://github.com/llvm/llvm-project/pull/218514