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.
We're going to remove the support for modules-ts. But there are a lot of
tests which uses -fmodules-ts. We shouldn't remove them simply. This
patch refactor these tests to use standard c++ modules.
The current version only emits the below error for a module (attempted to be loaded) from the `prebuilt-module-path`:
```
error: module file blabla.pcm cannot be loaded due to a configuration mismatch with the current compilation [-Wmodule-file-config-mismatch]
```
With this change, if the prebuilt module is used, we allow the proper diagnostic behind the configuration mismatch to be shown.
```
error: POSIX thread support was disabled in PCH file but is currently enabled
error: module file blabla.pcm cannot be loaded due to a configuration mismatch with the current compilation [-Wmodule-file-config-mismatch]
```
(A few lines later an error is emitted anyways, so there is no reason not to complain for configuration mismatches if a config mismatch is found and kills the build.)
Reviewed By: dblaikie
Tags: #clang
Differential Revision: https://reviews.llvm.org/D53334
llvm-svn: 346439
