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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/51965] Redundant move constructions in heap algorithms
Date: Sun, 29 Mar 2020 19:20:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D51965

--- Comment #19 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #16)
> (In reply to Marc Glisse from comment #5)
> > (The split into push_heap and __push_heap is just so the first part can=
 be
> > inlined without the second, right?)
> >=20
> > A more direct adaptation of the old code to rvalue references would be:
> >=20
> >       std::__push_heap(__first, _DistanceType((__last - __first) - 1),
> >                        _DistanceType(0), _ValueType(_GLIBCXX_MOVE(*(__l=
ast -
> > 1))));
>=20
> I tried doing this and it didn't seem to help the testcase attached here.

push_heap(): default_ctors=3D0, copy_ctors=3D0, copy_assignments=3D0, swaps=
=3D0,
[-cheap_dtors=3D1998,-] {+cheap_dtors=3D999,+} expensive_dtors=3D0,
[-move_ctors=3D1998,-] {+move_ctors=3D999,+} cheap_move_assignments=3D2201,
expensive_move_assignments=3D0, comparisons=3D2196

It doesn't help the other operations, but it has some effect on this one.=