[libc++] Add "REQUIRES: long_tests" to two libc++ tests

[miyuki]

Summary

Currently, we use the lit feature "long_tests" for libc++ tests that
take a long time to run so that they can be disabled by users.

This patch marks the following two tests:

• std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp
• numerics/rand/rand.dist/rand.dist.bern/rand.dist.bern.bin/eval.PR44847.pass.cpp

with "REQUIRES: long_tests".

The run time of these tests is similar to that of other tests already
marked as "long_tests". For example, on an x86-64 machine with an
i7-6700 CPU running at 3.4 GHz, an existing long test
std/numerics/rand/rand.dist/rand.dist.pois/rand.dist.pois.weibull/eval_param.pass.cpp
takes 1.07 seconds, whereas eval.PR44847.pass.cpp takes 1.27 seconds,
sort.pass.cpp takes 39.10 seconds.

[philnik]

I'm really not convinced that this flag makes any sense. Most importantly: A test on one machine could be very slow while it's negligible on another. Some tests that are marked long_tests take ~0.5 seconds on my machine, which is definitely not slow. Just having a timeout and the option to ignore timeouts in lit would make a lot more sense IMO.

[miyuki]

In D152439#4405979, @philnik wrote:

A test on one machine could be very slow while it's negligible on another. Some tests that are marked long_tests take ~0.5 seconds on my machine, which is definitely not slow.

Yes, I am running these tests on a simulator and eval.PR44847.pass.cpp takes ~10 minutes. I used x86 as an example because that's what others can use to reproduce the result.

Just having a timeout and the option to ignore timeouts in lit would make a lot more sense IMO.

But that would hide real bugs, e.g. miscompilations that create infinite loops.

[philnik]

In D152439#4406038, @miyuki wrote:

In D152439#4405979, @philnik wrote:

A test on one machine could be very slow while it's negligible on another. Some tests that are marked long_tests take ~0.5 seconds on my machine, which is definitely not slow.

Yes, I am running these tests on a simulator and eval.PR44847.pass.cpp takes ~10 minutes. I used x86 as an example because that's what others can use to reproduce the result.

Just having a timeout and the option to ignore timeouts in lit would make a lot more sense IMO.

But that would hide real bugs, e.g. miscompilations that create infinite loops.

Possibly, but these tests are for the library, not the compiler. Anyways, you can still keep a list of tests that time out and check that there isn't anything unexpected timing out. Given that the list of slow tests can be different on every platform, I don't see how we could keep a reasonable list of slow tests without losing coverage. Another option I just remembered is that you can disable specific tests through --filter-out.

libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
+// REQUIRES: long_tests
+
 // <algorithm>
 
 // template<RandomAccessIterator Iter>
 //   requires ShuffleIterator<Iter>
 //         && LessThanComparable<Iter::value_type>
 //   void
 //   sort(Iter first, Iter last);
 

libcxx/test/std/numerics/rand/rand.dist/rand.dist.bern/rand.dist.bern.bin/eval.PR44847.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <random>
 
+// REQUIRES: long_tests
+
 // template<class IntType = int>
 // class binomial_distribution
 
 // template<class _URNG> result_type operator()(_URNG& g);
 
 // Test the fix for https://llvm.org/PR44847.
 
 // Serializing/deserializing the state of the RNG requires iostreams