[PATCH] D126959: [C++20][Modules] Introduce an implementation module.

[Iain Sandoe via Phabricator via cfe-commits]

iains added a comment.

This was originally created (and @ChuanqiXu approved) for the work on module initialisers.  I did not apply it then, since it was possible to determine the correct state for the initialisers without it.

However, now we are trying to handle some of the details of different lookup requirements between same-module and same-TU, I think it is a foundation for that.  This also means that implementation units will get their own TU decl and have a distinct decl context (rather than the current case that we share the decl context of the interface).

The units are never serialised (as noted above) but we still need to allocate an extra bit for the enum (since we now have 9 values); this is not a significant load (since it adds only one bit to each module header).


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  https://reviews.llvm.org/D126959/new/

https://reviews.llvm.org/D126959