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.
Close https://github.com/llvm/llvm-project/issues/60544.
The root cause for the issue is that when we compile a module unit, the
file manager (and proprocessor and source manager) are owned by AST
instead of the compilaton instance. So the file manager may be invalid
when we want to create a time-report file for -ftime-trace when we are
compiling a module unit.
This patch tries to recreate the file manager for -ftime-trace if we
find the file manager is not valid.
