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* [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator
@ 2021-04-18 7:55 hewillk at gmail dot com
2021-04-18 8:09 ` [Bug libstdc++/100133] " hewillk at gmail dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: hewillk at gmail dot com @ 2021-04-18 7:55 UTC (permalink / raw)
To: gcc-bugs
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.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/100133] std::copy extremely slow for random access iterator
2021-04-18 7:55 [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator hewillk at gmail dot com
@ 2021-04-18 8:09 ` hewillk at gmail dot com
2021-04-18 17:22 ` hewillk at gmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: hewillk at gmail dot com @ 2021-04-18 8:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100133
--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> ---
And the libstdc++‘s std::copy is also 8.9 times slower than the equivalent
std::tranfrom:
#include <vector>
#include <list>
#include <algorithm>
const std::vector<int> v(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 transform_from_vector(benchmark::State& state)
{
for (auto _ : state) {
std::vector<int> to(v.size());
std::transform(
v.begin(), v.end(),
to.begin(),
[](int x) { return x; }
);
}
}
BENCHMARK(transform_from_vector);
you can see the benchmark here:
https://quick-bench.com/q/yuGf3npWpeU2EQhzzGud-aYNlNE. If using libc++,
std::copy is 2.2 times faster than std::transform as expected, see
https://quick-bench.com/q/3_V0EaU2jxnx4kSjWdarq7FOSh0.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/100133] std::copy extremely slow for random access iterator
2021-04-18 7:55 [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator hewillk at gmail dot com
2021-04-18 8:09 ` [Bug libstdc++/100133] " hewillk at gmail dot com
@ 2021-04-18 17:22 ` hewillk at gmail dot com
2021-04-18 17:28 ` hewillk at gmail dot com
2021-04-18 19:03 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: hewillk at gmail dot com @ 2021-04-18 17:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100133
--- Comment #2 from 康桓瑋 <hewillk at gmail dot com> ---
After actually executing the same code on my local and remote servers, I did
not produce such a result. In both cases, std::copy achieved the expected
high-efficiency performance, so I think this should only be Quick C++ Benchmark
Own question, thank you for your time
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/100133] std::copy extremely slow for random access iterator
2021-04-18 7:55 [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator hewillk at gmail dot com
2021-04-18 8:09 ` [Bug libstdc++/100133] " hewillk at gmail dot com
2021-04-18 17:22 ` hewillk at gmail dot com
@ 2021-04-18 17:28 ` hewillk at gmail dot com
2021-04-18 19:03 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: hewillk at gmail dot com @ 2021-04-18 17:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100133
康桓瑋 <hewillk at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
--- Comment #3 from 康桓瑋 <hewillk at gmail dot com> ---
(In reply to 康桓瑋 from comment #2)
> After actually executing the same code on my local and remote servers, I did
> not produce such a result. In both cases, std::copy achieved the expected
> high-efficiency performance, so I think this should only be Quick C++
> Benchmark
> Own question, thank you for your time
Close.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/100133] std::copy extremely slow for random access iterator
2021-04-18 7:55 [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator hewillk at gmail dot com
` (2 preceding siblings ...)
2021-04-18 17:28 ` hewillk at gmail dot com
@ 2021-04-18 19:03 ` redi at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2021-04-18 19:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100133
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|FIXED |INVALID
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This should be RESOLVED INVALID not RESOLVED FIXED, because nothing needed to
be fixed.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-04-18 19:03 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2021-04-18 7:55 [Bug libstdc++/100133] New: std::copy extremely slow for random access iterator hewillk at gmail dot com
2021-04-18 8:09 ` [Bug libstdc++/100133] " hewillk at gmail dot com
2021-04-18 17:22 ` hewillk at gmail dot com
2021-04-18 17:28 ` hewillk at gmail dot com
2021-04-18 19:03 ` redi at gcc dot gnu.org
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