Following of https://github.com/llvm/llvm-project/pull/76930
This follows the idea of "only writes what we writes", which I think is
the most natural and efficient way to implement this optimization.
We start writing the BMI from the first declaration in module purview
instead of the global module fragment, so that everything in the GMF
untouched won't be written in the BMI naturally.
The exception is, as I said in
https://github.com/llvm/llvm-project/pull/76930, when we write a
declaration we need to write its decl context, and when we write the
decl context, we need to write everything from it. So when we see
`std::vector`, we basically need to write everything under namespace
std. This violates our intention. To fix this, this patch delays the
writing of namespace in the GMF.
From my local measurement, the size of the BMI decrease to 90M from 112M
for a local modules build. I think this is significant.
This feature will be covered under the experimental reduced BMI so that
it won't affect any existing users. So I'd like to land this when the CI
gets green.
Documents will be added seperately.
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/60824
The form -fmodule-file=<path-to-BMI> will load modules eagerly and the
form -fmodule-file=<module-name>=<path-to-BMI> will load modules lazily.
The inconsistency adds many additional burdens to the implementations.
And the inconsistency looks not helpful and necessary neither. So I want
to deprecate the form -fmodule-file=<path-to-BMI> for named modules.
This is pretty helpful for us (the developers).
Does this change make any regression from the perspective of the users?
To be honest, yes. But I think such regression is acceptable. Here is
the example:
```
// M.cppm
export module M;
export int m = 5;
// N.cpp
// import M; // woops, we forgot to import M.
int n = m;
```
In the original version, the compiler can diagnose the users to import
`M` since the compiler have already imported M. But in the later style,
the compiler can only say "unknown identifier `m`".
But I think such regression doesn't make a deal since it only works if
the user put `-fmodule-file=M.pcm` in the command line. But how can the
user put `-fmodule-file=M.pcm` in the command line without `import M;`?
Especially currently such options are generated by build systems. And
the build systems will only generate the command line from the source
file.
So I think this change is pretty pretty helpful for developers and
almost innocent for users and we should accept this one.
I'll add the release notes and edit the document after we land this.
Differential Revision: https://reviews.llvm.org/D144707
Close https://github.com/llvm/llvm-project/issues/60488.
Previously, when we instantiate a template, the argument dependent
lookup is performed in the context of the instantiation, which implies that the
functions not visible in the context can't be found by the argument
dependent lookup.
But this is not true, according to [module.context]p3, the instantiation
context for the implicit instantiation of a template should contain the
context of the primary module interface if the template is defined in
the module interface unit.
Note that the fix didn't implemnet [module.context]p3 precisely, see the
comments for example.
