[PATCH] libstdc++ testsuite/std/ranges/iota/max_size_type.cc: Reduce /10 for simulators

[Jonathan Wakely]

On Sat, 30 Dec 2023, 01:41 Hans-Peter Nilsson, <hp@bitrange.com> wrote:

> I'm not completely sure I got the intent of the "log2_limit",
> or whether "limit" is sane to decrease like this; it just
> looked like an obvious and safe reduction.  Also, I verified
> the 10+ minute runtime, on this same host (clocked at 11:43.61
> elapsed time) for a r12-2797-g307e0d40367996 build that I
> happened to have kept around; likely the build that led up
> to that commit.  Now it's 58:45.78 elapsed time for a
> successful run.  Looks like a 5x performance regression.
> Worrisome; PR mentioned below.
>
> Incidentally, a parallel build and a serial test-run takes 9
> hours on that laptop, so that's almost 2 hours just for one
> test, if just updating the timeout to fit.  IOW, currently 48
> minutes out of 9 hours for one test that just times out.
>
> (That was just mentioned for comparison purposed: when suitable,
> I test with `nprocs`-1 in parallel.)
>
> I'll put it on the back-burner to investigate.  I think I'll
> try to graft that version of libstdc++-v3 to this version
>

Unfortunately that will probably be difficult.


and see if I can shift the blame away from MMIX code
> generation onto libstdc++-v3.  ;)
> Or perhaps the cause is known?
>

Not to me. It probably is a target codegen bug, since all this test really
does is emulate a wide integer type using masks and shifts.


> With this, the test successfully completes in ~34 seconds.
>
> Ok to commit?
>

Looks OK to me, but Patrick wrote this test so please wait for him to
confirm. I think this just reduces the number of cases tested, but doesn't
miss any important edge cases that should be checked.




> -- >8 --
> Looks like the MMIX port code quality and/or libstdc++
> performance of this test has regressed since
> r12-2799-ge9b639c4b53221 by a factor 5.  Anyway what was 11+
> minutes runtime then, is now at r14-6859-gd1eacedc6d9ba9
> close to 60 minutes.  Better prune the test, not just
> increase timeouts.  Also of course, investigate the
> performance regression, logged as PR113175.
>
>         * testsuite/std/ranges/iota/max_size_type.cc: Adjust
>         limits from -1000..1000 to -100..100 for simulators.
> ---
>  .../std/ranges/iota/max_size_type.cc          | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> index a1fbc3241dca..38fa6323d47e 100644
> --- a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> @@ -16,6 +16,7 @@
>  // <http://www.gnu.org/licenses/>.
>
>  // { dg-do run { target c++20 } }
> +// { dg-additional-options "-DSIMULATOR_TEST" { target simulator } }
>  // { dg-timeout-factor 4 }
>
>  #include <limits>
> @@ -31,6 +32,14 @@ using signed_rep_t = __int128;
>  using signed_rep_t = long long;
>  #endif
>
> +#ifdef SIMULATOR_TEST
> +#define LIMIT 100
> +#define LOG2_CEIL_LIMIT 7
> +#else
> +#define LIMIT 1000
> +#define LOG2_CEIL_LIMIT 10
> +#endif
> +
>  static_assert(sizeof(max_size_t) == sizeof(max_diff_t));
>  static_assert(sizeof(rep_t) == sizeof(signed_rep_t));
>
> @@ -199,8 +208,8 @@ test02()
>    using max_type = std::conditional_t<signed_p, max_diff_t, max_size_t>;
>    using shorten_type = std::conditional_t<shorten_p, hw_type, max_type>;
>    const int hw_type_bit_size = sizeof(hw_type) * __CHAR_BIT__;
> -  const int limit = 1000;
> -  const int log2_limit = 10;
> +  const int limit = LIMIT;
> +  const int log2_limit = LOG2_CEIL_LIMIT;
>    static_assert((1 << log2_limit) >= limit);
>    const int min = (signed_p ? -limit : 0);
>    const int max = limit;
> @@ -257,8 +266,8 @@ test03()
>    using max_type = std::conditional_t<signed_p, max_diff_t, max_size_t>;
>    using base_type = std::conditional_t<toggle_base_p, hw_type, max_type>;
>    constexpr int hw_type_bit_size = sizeof(hw_type) * __CHAR_BIT__;
> -  constexpr int limit = 1000;
> -  constexpr int log2_limit = 10;
> +  constexpr int limit = LIMIT;
> +  constexpr int log2_limit = LOG2_CEIL_LIMIT;
>    static_assert((1 << log2_limit) >= limit);
>    const int min = (signed_p ? -limit : 0);
>    const int max = limit;
> @@ -312,7 +321,7 @@ test03()
>  void
>  test04()
>  {
> -  constexpr int limit = 1000;
> +  constexpr int limit = LIMIT;
>    for (int i = -limit; i <= limit; i++)
>      {
>        VERIFY( -max_size_t(-i) == i );
> --
> 2.30.2
>
>
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