[llvm-dev] Proposal: introduce dependency on abseil when building benchmarks

Mircea Trofin via llvm-dev llvm-dev at lists.llvm.org
Thu Oct 7 08:05:59 PDT 2021

On Tue, Oct 5, 2021 at 9:37 PM Mehdi AMINI <joker.eph at gmail.com> wrote:

> On Tue, Oct 5, 2021 at 9:26 PM Mircea Trofin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>> On Tue, Oct 5, 2021 at 8:57 PM Reid Kleckner <rnk at google.com> wrote:
>>> On Thu, Sep 30, 2021 at 10:08 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.
>>> Could you please elaborate on which of these approaches will be used for
>>> LLVM? How will this affect regular LLVM developers?
>> Assuming regular LLVM developers means developers that don't enable
>> affected.
>> The current PR in "benchmarks" upstream is set up so that it will either
>> download the abseil dependency at build time, or, if the location of abseil
>> is specified via a cmake flag, then it uses that one (which covers the last
>> 2 options). I don't know if the first option is acceptable by those that
>> something I'm hoping to discover with this thread. If it is acceptable,
>> it's a transparent option, so it won't directly impact those users either.
> What should we expect in terms of ability to benchmark LLVM on various
> platforms / OSes? It seems like we will tie ourselves to Abseil, and I
> don't know anything about how their compatibility matrix compares to LLVM
> one? (and if it will continue being true in the foreseeable future?)

The goal isn't for benchmark to change its dependency matrix due to the new
dependency ( +dominic hamon <dominic at google.com> , please correct me). So
from the perspective of LLVM, this doesn't change anything. Granted, there
is now a strictly higher probability for breaking changes, if abseil
decides to change its support matrix and break benchmark, and thus affect
the latter's LLVM users.

> Thanks,
> --
> Mehdi
>>> ----
>>> This is truly unrelated, but I have a lot of feelings about this, and I
>>> will use this opportunity to inappropriately complain that the benchmarks
>>> library has been spamming me with cmake warnings about std::regex for
>>> years: https://bugs.llvm.org/show_bug.cgi?id=38874 The CMake step
>>> really ought to be warning-clean.
>> Ack. Added an issue on the project side:
>> https://github.com/google/benchmark/issues/1236 (maybe it has better
>> visibility)
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