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 adds a check for exported inline functions, that there is a definition in
the definition domain (which, in practice, can only be the module purview but
before any PMF starts) since the PMF definition domain cannot contain exports.
This is:
[dcl.inline]/7
If an inline function or variable that is attached to a named module is declared in
a definition domain, it shall be defined in that domain.
The patch also amends diagnostic output by excluding the PMF sub-module from the
set considered as sources of missing decls. There is no point in telling the user
that the import of a PMF object is missing - since such objects are never reachable
to an importer. We still show the definition (as unreachable), to help point out
this.
Differential Revision: https://reviews.llvm.org/D128328
