Reduce memory consumption of two ranges tests

[Casey Carter (CaseyCarter)]

By making the stateful lambda a namespace-scope function object (at the suggestion of the FE team) and reducing the combinatorics of the test matrix of range properties.

[Michael Schellenberger Costa (miscco)]

Thanks a lot, i started to also rely more on struct these days

[Alex Guteniev (AlexGuteniev)]

and reducing the combinatorics of the test matrix

Where? 👀

[Charlie Barto (barcharcraz)]

How much time/mem does the struct conversion alone save? Without running only "interesting" specializations?

[Stephan T. Lavavej (StephanTLavavej)]

I have pushed a trivial change to remove unnecessary test:: qualification, which looks more complicated than it is due to (desirable) clang-format reflowing.

[Stephan T. Lavavej (StephanTLavavej)]

Casey Carter (@CaseyCarter)

and reducing the combinatorics of the test matrix

Alex Guteniev (@AlexGuteniev)

Where? 👀

I believe that this is happening, not in the meow_matrix.lst, but in replacing the runtime call to test_in_write<instantiator, const P, P>(); (now guarded by TEST_EVERYTHING) with a few specific lines of instantiator::call.

[Casey Carter (CaseyCarter)]

and reducing the combinatorics of the test matrix

Where? 👀

The body of main. The previous body is still there under #ifdef TEST_EVERYTHING. test_in_write:

STL/tests/std/include/range_algorithm_support.hpp

Lines 1295 to 1298 in 0349ce1

	template <class Instantiator, class Element1, class Element2>
	constexpr void test_in_write() {
	with_input_ranges<with_writable_iterators<Instantiator, Element2>, Element1>::call();
	}

generates calls to instantiator::call with the cross product of "all variations of input range properties" (about 55 cases):

STL/tests/std/include/range_algorithm_support.hpp

Lines 1047 to 1086 in 0349ce1

	// For all ranges, IsCommon implies Eq.
	// For single-pass ranges, Eq is uninteresting without IsCommon (there's only one valid iterator
	// value at a time, and no reason to compare it with itself for equality).
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::no, Common::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::no, Common::no, CanCompare::no, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::no, Common::yes, CanCompare::yes, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::no, Common::yes, CanCompare::yes, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::yes, Common::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::yes, Common::no, CanCompare::no, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::yes, Common::yes, CanCompare::yes, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::no, CanDifference::yes, Common::yes, CanCompare::yes, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::no, Common::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::no, Common::no, CanCompare::no, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::no, Common::yes, CanCompare::yes, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::no, Common::yes, CanCompare::yes, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::yes, Common::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::yes, Common::no, CanCompare::no, ProxyRef::yes>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::yes, Common::yes, CanCompare::yes, ProxyRef::no>>();
	Continuation::template call<Args...,
	range<input, Element, Sized::yes, CanDifference::yes, Common::yes, CanCompare::yes, ProxyRef::yes>>();
	with_forward_ranges<Continuation, Element>::template call<Args...>();

and "all variations of writable iterator properties" (about 15 cases):

STL/tests/std/include/range_algorithm_support.hpp

Lines 898 to 904 in 0349ce1

	// Diff and Eq are not significant for "lone" single-pass iterators, so we can ignore them here.
	Continuation::template call<Args...,
	iterator<input, Element, CanDifference::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	iterator<input, Element, CanDifference::no, CanCompare::no, ProxyRef::yes>>();
	with_output_iterators<Continuation, Element>::template call<Args...>();

for a total of 15 * 55 = 825 specializations tested. This is replaced by directly calling instantiator::call five different ways. We know this is adequate coverage only by knowing the details of the implementation.

[Casey Carter (CaseyCarter)]

How much time/mem does the struct conversion alone save?

I only measured remove_copy. (Xiang Fan (@xiangfan-ms) reported similar numbers for remove_copy_if which was motivation enough for me to add it without measuring myself.) Only this change affects the maximum memory size, which went from 5.8GB to 125MB. The corresponding reduction in runtime for all 17 test configs on my 3950X was (IIRC) 90 seconds down to the low twenties.

Without running only "interesting" specializations?

This further reduced total runtime down to about 2.5 seconds.

[Stephan T. Lavavej (StephanTLavavej)]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks for dramatically improving the resource consumption of these tests! 🐱 🎉 📉

[Osyotr (Osyotr)]

How could this lambda cause this extensive memory consumption?

[Michael Schellenberger Costa (miscco)]

How could this lambda cause this extensive memory consumption?

Every time when we instantiate the function, we create a new stateful lambda. And we instantiate that function a ton