[llvm-dev] Incrementally compiling LLVM

[Mehdi AMINI via llvm-dev]

On Wed, Apr 14, 2021 at 12:59 PM Francesco Bertolaccini via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On 14/04/2021 21:18, David Blaikie wrote:
> > Sounds like something's going wrong for sure. How are you measuring
> > the time? (how much time is it taking) and what are you testing by
> > "partial recompilation"? Touching an ADT .h file is likely to
> > recompile nearly everything so might not be much better than a clean
> > build - but touching a .cpp file (especially a .cpp file for a single
> > tool, rather than a library) might be quite quick. So try timing a
> > full clean build (ninja -t clean, ninja clang) and then incrementally
> > touching just a .cpp file (eg: clang/tools/driver/driver.cpp  ) and
> > see how they compare
>
> I currently do not have sufficient resources to compile LLVM on my
> personal machine, so I am (ab?)using GitHub Actions. My workflow is
> setup such that the build artifacts are cached and restored on every
> worflow run. The time is measured automatically by GitHub itself, and is
> around ~2h for each run, whether from scratch or starting from the cache.
>

For doing incremental compilation in such a context, I'd try to enable some
sort of CCACHE instead, we have this on a bot and it's quite effective in
this context!

It's not using GitHub actions thought, but here is a recipe for GitHub
actions (I haven't tried it):
https://cristianadam.eu/20200113/speeding-up-c-plus-plus-github-actions-using-ccache/

Best,

-- 
Mehdi


> I don't generally edit .h files directly, unless they are generated by
> modifying TableGen files.
>
> The fact that someone else has successfully been able to do incremental
> builds _does_ make it seem like it's a configuration issue on my part.
>
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