[llvm-dev] [cfe-dev] FYI: ENABLE_MODULES would make building faster

Serge Preis via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 12 01:02:02 PDT 2017

There is nice presentation from google on what it takes to enable modules in massively parallel and distributed build system:

Best regards,

12.07.2017, 14:18, "Boris Kolpackov via cfe-dev" <cfe-dev at lists.llvm.org>:
> David Blaikie via cfe-dev <cfe-dev at lists.llvm.org> writes:
>>  I have some hope/aspirations of implementing explicit modules* support in
>>  cmake & so it'll be interesting to compare how much more parallelism can be
>>  achieved by that.
> I think it will be hard to implement this "properly" in CMake until the
> underlying build systems are module-aware, similar to how (most) of them
> being header-aware. Specifically, generating all the .pcm's during some
> sort of a pre-build step will hinder parallelism since in a sense you will
> have a "barrier" between compiling module interfaces and other sources.
> Ideally, you would want to start compiling sources as soon as all the
> module interfaces that they actually use are ready. Especially so if
> you have a -j72 kind of machine ;-).
> Then there is the issue of change detection: you probably don't want to
> make all your sources depend on all your module interfaces.
> FWIW, we have implemented this "proper" module support (though for
> -fmodule-ts only) in build2[1], if you (or anyone else) would like
> to try it.
> [1] https://build2.org/
> Boris
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