From: "Cristian Rodríguez" <crrodriguez@opensuse.org>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>,
"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Missing optimization: mempcpy(3) vs memcpy(3)
Date: Mon, 12 Dec 2022 11:57:36 -0300 [thread overview]
Message-ID: <CAPBLoAcL=5bZaQ_XvoNJEtHBeChNrkXb2orPMwYXEErb6Wg5Kg@mail.gmail.com> (raw)
In-Reply-To: <PAWPR08MB898243076FBFBF6C7E919E4183E29@PAWPR08MB8982.eurprd08.prod.outlook.com>
On Mon, Dec 12, 2022 at 11:35 AM Wilco Dijkstra via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> Hi,
>
> I don't believe there is a missing optimization here: compilers expand mempcpy
> by default into memcpy since that is the standard library call. That means even
> if your source code contains mempcpy, there will never be any calls to mempcpy.
>
> The reason is obvious: most targets support optimized memcpy in the C library
> while very few optimize mempcpy. The same is true for bzero, bcmp and bcopy.
>
> Targets can do it differently, IIRC x86 is the only target that emits calls both to
> memcpy and mempcpy.
yeah, x86_64 at least uses both, but I think open coded mempcpy needs
to be transformed into a library call anyway.
Other optimizations that are actually missing are:
- the cases where of snprintf %s could become memccpy
- open coded memccpy could also be turned into library calls.
next prev parent reply other threads:[~2022-12-12 14:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-12 14:34 Wilco Dijkstra
2022-12-12 14:57 ` Cristian Rodríguez [this message]
-- strict thread matches above, loose matches on Subject: below --
2022-12-09 17:11 Alejandro Colomar
2022-12-12 13:37 ` Martin Liška
2022-12-12 13:44 ` Alejandro Colomar
2022-12-12 13:56 ` Jakub Jelinek
2022-12-12 14:05 ` Alejandro Colomar
2022-12-12 14:48 ` Jonathan Wakely
2022-12-12 14:53 ` Jakub Jelinek
2022-12-12 15:56 ` Alejandro Colomar
2022-12-12 16:09 ` Jakub Jelinek
2022-12-12 17:15 ` Alejandro Colomar
2022-12-12 17:42 ` Jonathan Wakely
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