https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100133
Bug ID: 100133
Summary: std::copy extremely slow for random access iterator
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
HI, I found that libstdc++‘s std::copy is extremely slow for random access
iterator. For the following example, if libc++'s std::copy is used, copy from
std::vector will be 10 times faster than from std::list with -O3, but for
libstdc++'s std::copy, copying from std::vector is twice as slow as std::list.
#include <vector>
#include <list>
#include <algorithm>
const std::vector<int> v(100, 42);
const std::list<int> l(100, 42);
static void copy_from_vector(benchmark::State& state)
{
for (auto _ : state) {
std::vector<int> to(v.size());
std::copy(
v.begin(), v.end(),
to.begin()
);
}
}
BENCHMARK(copy_from_vector);
static void copy_from_list(benchmark::State& state)
{
for (auto _ : state) {
std::vector<int> to(l.size());
std::copy(
l.begin(), l.end(),
to.begin()
);
}
}
BENCHMARK(copy_from_list);
you can see libc++‘s std::copy benchmark here:
https://quick-bench.com/q/OPrNMQpJf6jKPBT5G-Uq-4U6XHc
and libstdc++'s std::copy here:
https://quick-bench.com/q/cuKCK_VE-KJgD3xA-ogXNCj9UCQ.
