[llvm] [AArch64](NFC) Introduce unified `isLegalArithImmed()` and `isLegalCmpImmed()` (PR #203020)

[David Green via llvm-commits]

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@@ -350,6 +350,28 @@ static inline bool isValidDecodeLogicalImmediate(uint64_t val,
   return true;
 }
 
+// isLegalArithImmed - \returns true if \p C is a legal immediate operand for an
+// arithmetic instruction.
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davemgreen wrote:

///'s for doxygen comment.

https://github.com/llvm/llvm-project/pull/203020