[clang] [Clang] Add __builtin_counted_by_ref builtin (PR #114495)

[Yeoul Na via cfe-commits]

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@@ -16,6 +16,8 @@ void test1(struct fam_struct *ptr, int size, int idx) {
 
   *__builtin_counted_by_ref(ptr->array) = size;             // ok
   *__builtin_counted_by_ref(&ptr->array[idx]) = size;       // ok
+  *__builtin_counted_by_ref(&ptr->array) = size;            // ok
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rapidsna wrote:

I guess this will just work too? `*__builtin_counted_by_ref(ptr->array[idx]) = size;` 

Do you have a use case? I'd prefer these being ill-formed because the user might find it working unexpectedly. But I don't have a strong opinion on this. I'd leave it up to you/Linux users if you find this would be useful.

https://github.com/llvm/llvm-project/pull/114495