Re: [gentoo-dev] Re: LLVM build strategy

["Michał Górny" <mgorny@gentoo.org>]

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On Sun, 2024-12-08 at 17:23 -0500, Eli Schwartz wrote:
> On 12/8/24 4:45 PM, Sam James wrote:
> > > I don't like the idea of spending hours building everything before I'm
> > > even able to start running tests, just to learn that LLVM is broken
> > > and there's no point in even starting to build the rest.
> > 
> > I don't follow this bit -- you need the new LLVM merged before you can
> > build Clang's tests, right? And if any of it fails to build, it's not
> > like we can commit the release or snapshot?
> > 
> > What am I missing on this bit?
> 
> 
> I think the point here is that currently, one can build sys-devel/llvm
> with tests enabled, and if it fails, there's no point in also building
> sys-devel/clang. But with a monorepo build, you'd have to build llvm,
> clang (and various others) first, and then launch tests for llvm and
> clang together, only to get a test failure in the llvm tests that
> indicates everything else is broken too. Depending on cmake test
> ordering, you may also run half the clang tests before hitting the llvm
> failures, even.

Exactly.  You have to compile everything first, before you start testing
anything.

And I don't think testing order is predictable either. I mean,
technically we could just issue check-llvm, check-clang, and so on
manually, but that's going to be messy and I'm not even sure if I can
figure out all the correct targets to avoid duplication.

And if you think we could hack this around by stubbing src_compile()
and having tests compile things component after component...
the dependencies are pretty much broken everywhere, and you do need to
compile everything before you run check-* targets.

> In theory this could be solved by building monorepo-llvm with
> FEATURES=test USE="-clang" to start running tests, and then if that
> passes, rebuild llvm again but this time with clang etc. enabled. Not
> sure this is actually solving the stated objection...

ccache will save most of the time on rebuilding the same things (except
for tablegen or sphinx, which are pretty slow too), but you'd still be
rerunning the same tests.

-- 
Best regards,
Michał Górny


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