RE: EXT: Re: [PATCH] [libstdc++] [testsuite] require cmath for [PR114359]

["Chen, Yee Men (GE Vernova)" <yeemen.chen@ge.com>]

Hi,

Please raise a defect.

Yee Men

-----Original Message-----
From: Jonathan Wakely <jwakely@redhat.com> 
Sent: Thursday, June 13, 2024 11:42 AM
To: Alexandre Oliva <oliva@adacore.com>
Cc: gcc-patches@gcc.gnu.org; libstdc++@gcc.gnu.org
Subject: EXT: Re: [PATCH] [libstdc++] [testsuite] require cmath for [PR114359]

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On Thu, 13 Jun 2024 at 08:27, Alexandre Oliva <oliva@adacore.com> wrote:
>
>
> When !_GLIBCXX_USE_C99_MATH_TR1, binomial_distribution doesn't use the 
> optimized algorithm that was fixed in response to PR114359.  Without 
> that optimized algorithm, operator() ends up looping very very long 
> for the test, to the point that it would time out by several orders of 
> magnitude, without even exercising the optimized algorithm that we're 
> testing for regressions.  Arrange for the test to be skipped if that 
> bit won't be exercised.
>
> Regstrapped on x86_64-linux-gnu, also tested with gcc-13 
> x-aarch64-rtems6, where the problem was detected.  Ok to install?

OK.

This finding suggests we shouldn't even bother defining binomial_distribution without the <cmath> functions. It doesn't seem useful if it's that slow (or is that just because this test uses 1<<30 as the t parameter?)

Either way, the change to the test is fine.

>
>
> for  libstdc++-v3/ChangeLog
>
>         PR libstdc++/114359
>         * testsuite/26_numerics/random/binomial_distribution/114359.cc:
>         Require cmath.
> ---
>  .../random/binomial_distribution/114359.cc         |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git 
> a/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/1143
> 59.cc 
> b/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/1143
> 59.cc index c1e4c380bf91d..12d967dcbfd34 100644
> --- 
> a/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/1143
> 59.cc
> +++ b/libstdc++-v3/testsuite/26_numerics/random/binomial_distribution/
> +++ 114359.cc
> @@ -2,6 +2,19 @@
>
>  // Bug 114359 - std::binomial_distribution hangs in infinite loop
>
> +// { dg-require-cmath "" }
> +
> +// The requirement above is not strictly true.  The test should work 
> +// without cmath, and it probably does, but without cmath, // 
> +binomial_distribution::operator() skips the optimized algorithm and 
> +// calls _M_waiting to loop a gazillion times.  On aarch64-rtems6 // 
> +qemu, that loop takes over 5 minutes to go through a small fraction 
> +// of the iteration space (__x at 22k, limited at 1G; __sum at 2e-5, 
> +// limited at 0.69).  The bug we're regression-testing here was in 
> +the // cmath-requiring bit, so even if this could conceivably not 
> +time out // on a really fast machine, there's hardly any reason to 
> +exercise // this extreme case.
> +
>  #include <random>
>
>  int main()
>
> --
> Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
>    Free Software Activist                   GNU Toolchain Engineer
> More tolerance and less prejudice are key for inclusion and diversity 
> Excluding neuro-others for not behaving ""normal"" is *not* inclusive
>