[llvm] [NFC][TableGen] Code cleanup in CodeGenRegister (PR #137994)

[Jason Eckhardt via llvm-commits]

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@@ -185,7 +185,7 @@ class CodeGenRegister {
 
   CodeGenRegister(const Record *R, unsigned Enum);
 
-  StringRef getName() const;
+  StringRef getName() const { return TheDef->getName(); }
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nvjle wrote:

The original asserted/validated `TheDef`, should it be here too?

https://github.com/llvm/llvm-project/pull/137994