[libc++][test] Bogus loops in time.cal.ymdlast.nonmembers/comparisons.pass.cpp

[StephanTLavavej]

Recently introduced by @mordante's #98169.

MSVC's /analyze complains:

D:\GitHub\STL\llvm-project\libcxx\test\std\time\time.cal\time.cal.ymdlast\time.cal.ymdlast.nonmembers\comparisons.pass.cpp(62) : warning C6294: Ill-defined for-loop.  Loop body not executed.
D:\GitHub\STL\llvm-project\libcxx\test\std\time\time.cal\time.cal.ymdlast\time.cal.ymdlast.nonmembers\comparisons.pass.cpp(63) : warning C6294: Ill-defined for-loop.  Loop body not executed.

This warning is usually a nuisance (complaining about loops that intentionally perform no iterations; calling them "ill-defined" isn't great either), but in this case it found actually-squirrely code 🐿️ :

llvm-project/libcxx/test/std/time/time.cal/time.cal.ymdlast/time.cal.ymdlast.nonmembers/comparisons.pass.cpp

Lines 61 to 68 in 7e7a906

	// same month, different years
	for (int i = 1000; i < 20; ++i)
	for (int j = 1000; j < 20; ++j)
	assert((testOrder(year_month_day_last{year{i}, month_day_last{January}},
	year_month_day_last{year{j}, month_day_last{January}},
	i == j ? std::strong_ordering::equal
	: i < j ? std::strong_ordering::less
	: std::strong_ordering::greater)));

I'm not sure what this code was intended to be doing. It appears that "same month, different years" previously looped from 1000 to 2000. Perhaps 1000 * 1000 = 1 million nested iterations was excessive, and the code should be looping from (say) 1000 to 1020?

[mordante]

Thanks for reporting this!

I'm not sure what this code was intended to be doing. It appears that "same month, different years" previously looped from 1000 to 2000. Perhaps 1000 * 1000 = 1 million nested iterations was excessive, and the code should be looping from (say) 1000 to 1020?

Not just excessive, but it exceeds the number of constexpr steps allowed by the compiler. In differfent tests I changed the range to 1000 to 1010 so I'll do the same here.