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From: "dartdart26 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/101923] std::function's move ctor is slower than the
 copy one for empty source objects
Date: Mon, 16 Aug 2021 07:18:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101923

--- Comment #3 from Petar Ivanov <dartdart26 at gmail dot com> ---
Thank you for pointing the output on x86!

Following that, I checked O2 and O3 on ARM64 and I see differences, though I
cannot say what their actual impact is:

02: https://godbolt.org/z/P9Garznef

O3: https://godbolt.org/z/Yb1q33YP3

In terms of x86, I ran the benchmark in Quick Bench (I assume x86 as that w=
hat
the disassembly is) and the results are similar to my findings on ARM64 - m=
ove
being slower:
https://quick-bench.com/q/vK9eSYngutKGo4QSPcdra9gUOI0

The benchmark code seems correct to me, but I might be missing something, m=
ight
be misusing DoNotOptimize() or there might be some side effects.

I am sure this is not a big deal. I was just wondering if adding an if
statement is doable and, if yes, it seems like a quick and easy win.=