[PATCH] D77592: [NFC][CodeGen] Add enum for selecting the layout of components in the vtable

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

I'm not sure if the AST-level v-table layout abstraction really cares about these differences.  I don't think it vends byte offsets into the v-table, just slot indices (i.e. word offsets).



================
Comment at: clang/include/clang/AST/VTableBuilder.h:380
+    /// other structs/functions.
+    Relative,
+  };
----------------
The only "struct" pointed to by the v-table is the `type_info` object.  How are you planning to handle that?  The standard ABI makes the `type_info` a vague-linkage symbol in most cases, so you won't be able to have a direct relative reference to it.  If you adopt the Apple ARM64 modification for `type_info` equality, you can rely on the `type_info` being defined within the same linkage unit unless the v-table is being emitted as an optimization for a type defined with a key function in a different linkage unit.  You could handle that by making this an "inidirectable" relative reference, where it's either a direct relative reference or a relative reference to a GOT entry, as specified by the low bit in the reference.  But you need *some* solution for this.


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https://reviews.llvm.org/D77592