[clang] [clang][Interp] Support AddOffset with 128bit offsets (PR #68679)

[Erich Keane via cfe-commits]

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@@ -1437,7 +1437,7 @@ bool OffsetHelper(InterpState &S, CodePtr OpPC, const T &Offset,
     return false;
   };
 
-  unsigned MaxOffset = MaxIndex - Ptr.getIndex();
+  T MaxOffset = T::from(MaxIndex - Ptr.getIndex(), Offset.bitWidth());
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erichkeane wrote:

Should MaxIndex just be a `T` as well?  I wonder if this function should just be 'fully dedicated' to being `T` instead of just this 1 variable here?

https://github.com/llvm/llvm-project/pull/68679