https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63400
--- Comment #16 from Vadim Zeitlin <vz-gcc at zeitlins dot org> ---
(In reply to Jonathan Wakely from comment #15)
> (In reply to Jonathan Wakely from comment #14)
> > Or maybe the testcase makes invalid assumptions and isn't really measuring
> > what it thinks it's measuring?
>
> e.g. maybe clock_getres says 100ns even though the clocks aren't really that
> precise.
No, the clock is not precise. The original test case
int main() {
for (unsigned long long size = 1; size < 10000000; size *= 10) {
auto start = std::chrono::high_resolution_clock::now();
std::vector<int> v(size, 42);
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = end - start;
std::cout << size << ": " << elapsed.count() << '\n';
}
}
outputs the following under Linux
% ./a.out
1: 436
10: 114
100: 80
1000: 1019
10000: 9499
100000: 104850
1000000: 686436
and this under Windows:
% ./a.exe
1: 1000
10: 0
100: 0
1000: 1000
10000: 9000
100000: 69000
1000000: 523000
