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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/94295] use __builtin_operator_new and
 __builtin_operator_delete when available
Date: Tue, 24 Mar 2020 20:44:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94295

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Smith from comment #2)
> (In reply to Marc Glisse from comment #1)
> > (In reply to Richard Smith from comment #0)
> > > The C++ language rules do not permit optimization (eg, deletion) of d=
irect
> > > calls to 'operator new' and 'operator delete'.
> >=20
> > I thought that was considered a bug?
>=20
> No, it's intentional: if the user directly calls '::operator new(42)' and
> they've replaced that function, the replacement function is guaranteed to=
 be
> called. In this regard, 'operator new' is just a regular function with a
> funny name.
>=20
> To be clear, the implicit call to 'operator new' produced by, say, 'new i=
nt'
> *is* optimizable, but a direct explicit call to 'operator new(sizeof(int)=
)'
> is not.
>=20
> > Gcc does optimize those, like it does malloc/free...
>=20
> That sounds like non-conforming behavior.


PR 23383 is where part of the discussion was done.

In fact GCC implements the optimization without the builtin:
https://gcc.gnu.org/legacy-ml/gcc-patches/2019-07/msg00136.html=