Close https://github.com/llvm/llvm-project/issues/71034
See
https://discourse.llvm.org/t/rfc-c-20-modules-introduce-thin-bmi-and-decls-hash/74755
This patch introduces reduced BMI, which doesn't contain the definitions
of functions and variables if its definitions won't contribute to the
ABI.
Testing is a big part of the patch. We want to make sure the reduced BMI
contains the same behavior with the existing and relatively stable
fatBMI. This is pretty helpful for further reduction.
The user interfaces part it left to following patches to ease the
reviewing.
This comes from https://reviews.llvm.org/D153003
By @rsmith, the test case is valid since:
> Per [temp.type]/1.4 (http://eel.is/c++draft/temp.type#1.4),
>
>> Two template-ids are the same if [...] their corresponding template
>> template-arguments refer to the same template.
> so B<A> and B<NS::A> are the same type. The stricter "same sequence of
> tokens" rule doesn't apply here, because using-declarations are not
> definitions.
> we should either (preferably) be including only the syntactic form of
> the base specifier (because local syntax is what the ODR covers), or
> the canonical type (which should be the same for both
> using-declarations).
Here we adopt the second suggested solutions.
Reviewed By: cor3ntin, v.g.vassilev
Differential Revision: https://reviews.llvm.org/D154324
