[clang] [CIR] Upstream support for null and virtual method pointers (PR #176522)

[Sirui Mu via cfe-commits]

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@@ -331,15 +343,30 @@ Attribute MethodAttr::parse(AsmParser &parser, Type odsType) {
     return get(ty, symbol);
   }
 
-  return {};
+  // Parse a uint64 that represents the vtable offset.
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Lancern wrote:

Add a round-trip test for the new parser and printer.

https://github.com/llvm/llvm-project/pull/176522