From: Noah Goldstein <goldstein.w.n@gmail.com>
To: "Christoph Müllner" <cmuellner@gcc.gnu.org>
Cc: GNU C Library <libc-alpha@sourceware.org>,
GCC Development <gcc@gcc.gnu.org>,
Florian Weimer <fweimer@redhat.com>,
Joseph Myers <joseph@codesourcery.com>
Subject: Re: [libc-coord] Add new ABI '__memcmpeq()' to libc
Date: Wed, 22 Sep 2021 13:15:24 -0500 [thread overview]
Message-ID: <CAFUsyf+i9hFE3WE_2PL=tt9RzU3Jv1N6qsrkEtxY9XLBo+avOw@mail.gmail.com> (raw)
In-Reply-To: <CAHB2gtRi03WYPGRVmW=q0X=sm9a9AksNxvH6aT9JR-5=fDLXKw@mail.gmail.com>
On Wed, Sep 22, 2021 at 12:46 PM Christoph Müllner <cmuellner@gcc.gnu.org>
wrote:
> Would it make sense to extend this proposal to include __strcmpeq()
> and __strncmpeq()?
>
> Both are already available internally in GCC in form of
> BUILT_IN_STRCMP_EQ and BUILT_IN_STRNCMP_EQ
> (tree-ssa-strlen.c detects them in handle_builtin_string_cmp() and
> builtins.c tries to inline them in expand_builtin_memcmp()).
> However, they are currently restricted to cases where the length of
> the string or the size of the array (of both arguments) is known.
>
> A use case for strcmpeq() would be the comparison of std::type_info
> objects (equality and inequality operator) in libstdc++.
>
> I agree and am happy to implement them along side __memcmpeq()
if the proposal is accepted. Do they need a seperate writeup with full
specifications?
> On Tue, Sep 21, 2021 at 9:54 PM Noah Goldstein via Gcc <gcc@gcc.gnu.org>
> wrote:
> >
> > On Fri, Sep 17, 2021 at 9:27 AM Florian Weimer via Libc-alpha <
> > libc-alpha@sourceware.org> wrote:
> >
> > > * Joseph Myers:
> > >
> > > > I was supposing a build-time decision (using
> > > GCC_GLIBC_VERSION_GTE_IFELSE
> > > > to know if the glibc version on the target definitely has this
> > > function).
> > > > But if we add a header declaration, you could check for __memcmpeq
> being
> > > > declared (and so cover arbitrary C libraries, not just glibc, and
> avoid
> > > > issues of needing to disable this logic for freestanding
> compilations,
> > > > which would otherwise be an issue if a glibc-target toolchain is used
> > > for
> > > > a freestanding kernel compilation). The case of people calling
> > > > __builtin_memcmp (or declaring memcmp themselves) without string.h
> > > > included probably isn't one it's important to optimize.
> > >
> > > The header-less case looks relevant to C++ and other language front
> > > ends, though. So a GCC_GLIBC_VERSION_GTE_IFELSE check could still make
> > > sense for them.
> > >
> > > (Dropping libc-coord.)
> > >
> > > Thanks,
> > > Florian
> > >
> > >
> > What are we going with?
> >
> > Should I go forward with the proposal in GLIBC?
> >
> > If I should go forward with it should I include a def in string.h?
>
next prev parent reply other threads:[~2021-09-22 18:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-16 17:02 Noah Goldstein
2021-09-16 17:55 ` [libc-coord] " Chris Kennelly
2021-09-16 18:31 ` Noah Goldstein
2021-09-16 20:32 ` Chris Kennelly
2021-09-16 20:35 ` Joseph Myers
2021-09-16 20:55 ` enh
2021-09-17 7:43 ` Richard Biener
2021-09-17 8:08 ` Florian Weimer
2021-09-17 8:31 ` Richard Biener
2021-09-17 8:37 ` Florian Weimer
2021-09-17 9:30 ` Richard Biener
2021-09-17 17:40 ` Noah Goldstein
2021-09-17 9:12 ` Jakub Jelinek
2021-09-17 16:55 ` Martin Sebor
2021-09-17 14:19 ` Joseph Myers
2021-09-17 14:26 ` Florian Weimer
2021-09-21 19:53 ` Noah Goldstein
2021-09-22 17:46 ` Christoph Müllner
2021-09-22 18:15 ` Noah Goldstein [this message]
2021-09-16 21:27 ` James Y Knight
2021-09-16 21:42 ` Joseph Myers
2021-09-16 21:50 ` enh
2021-09-16 21:59 ` Noah Goldstein
2021-09-16 22:17 ` Chris Kennelly
2021-09-16 22:36 ` Joseph Myers
2021-09-16 23:24 ` Noah Goldstein
2021-09-18 1:36 ` James Y Knight
2021-10-26 22:47 ` Noah Goldstein
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