llvm dev - Oct 2021 - Proposal: introduce dependency on abseil when building benchmarks

> On Sep 30, 2021, at 10:07 AM, Mircea Trofin via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> TL;DR; When either of LLVM_BUILD_BENCHMARKS or LIBCXX_INCLUDE_BENCHMARKS
are enabled, as well as for llvm-test-suite, a dependency to abseil would either
be auto-downloaded by the build system, or need to be user-specifiable, or
provided in the source tree.
FWIW: I'm not a fan of auto-downloading stuff. That's just a sneaky to
add a dependency that sure may not give trouble to the users where the
auto-download succeeds. But many companies have their build farms isolated from
the internet and security people would not be happy if we just download a blob
of code from a separate project that can change somewhat unnoticed by users of
LLVM.

Can't we copy the thing into the LLVM repository (aka vendoring) like we
copied the benchmark library? I feel that things become a different story when
we actually add dependencies...

- Matthias

On Thu, Oct 7, 2021 at 6:57 PM Matthias Braun <matthiasb at fb.com> wrote:
>
>
> > On Sep 30, 2021, at 10:07 AM, Mircea Trofin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > TL;DR; When either of LLVM_BUILD_BENCHMARKS or
LIBCXX_INCLUDE_BENCHMARKS
> are enabled, as well as for llvm-test-suite, a dependency to abseil would
> either be auto-downloaded by the build system, or need to be
> user-specifiable, or provided in the source tree.
>
> FWIW: I'm not a fan of auto-downloading stuff. That's just a sneaky
to add
> a dependency that sure may not give trouble to the users where the
> auto-download succeeds. But many companies have their build farms isolated
> from the internet and security people would not be happy if we just
> download a blob of code from a separate project that can change somewhat
> unnoticed by users of LLVM.
>
> Can't we copy the thing into the LLVM repository (aka vendoring) like
we
> copied the benchmark library? I feel that things become a different story
> when we actually add dependencies...
>
That is one of the options available in the proposed change in the
benchmark project upstream (the 'provided in the source tree' option).
So
if we decided, in LLVM, that we wanted to update the forks we have of the
benchmark project (assuming the other issues mentioned on this thread were
resolved), then it's up to us to set it up like you described.

> - Matthias
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Perhaps an unpopular opinion, but I don't see the value proposition in
foundation things like benchmark taking such convenience dependencies.
Abseil is not a lightweight dependency, either from the code or the build
system perspective, and it will limit portability (such a thing is hard to
prove, but I can speak from experience, being a downstream that has taken
the time to scalpel Abseil out in order to achieve better compatibility and
footprint).

In my experience, there are typically a small handful of things that
actually boost such a project (usually related to strings and collections).
For foundation components, I would far rather see such things forked in if
needed vs adding a hard dependency. Even better if components like abseil
were unobtrusive in keeping things separated for this form of sharing.

My project will most likely fork benchmark or switch to something lighter
if it goes down this path. LLVM can of course take its own path but I
generally consider forking when I see foundation components start down the
path of losing control of their dependencies.



On Thu, Oct 7, 2021, 6:57 PM Matthias Braun via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
>
> > On Sep 30, 2021, at 10:07 AM, Mircea Trofin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > TL;DR; When either of LLVM_BUILD_BENCHMARKS or
LIBCXX_INCLUDE_BENCHMARKS
> are enabled, as well as for llvm-test-suite, a dependency to abseil would
> either be auto-downloaded by the build system, or need to be
> user-specifiable, or provided in the source tree.
>
> FWIW: I'm not a fan of auto-downloading stuff. That's just a sneaky
to add
> a dependency that sure may not give trouble to the users where the
> auto-download succeeds. But many companies have their build farms isolated
> from the internet and security people would not be happy if we just
> download a blob of code from a separate project that can change somewhat
> unnoticed by users of LLVM.
>
> Can't we copy the thing into the LLVM repository (aka vendoring) like
we
> copied the benchmark library? I feel that things become a different story
> when we actually add dependencies...
>
> - Matthias
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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