From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 515D53858D38; Tue, 21 Nov 2023 14:17:55 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 515D53858D38
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1700576275;
	bh=AhGpDhYOLTDRgcmv4v+RGkgoyTenwbaBmwgIZOnH7Pg=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=d27CWOOiJxCViQEjGDpK9E0+++Jd8yVuMqUxjAmDdgLgtiCyQVNVerh/i6hiCUjaF
	 6+tV/2W4lENFfndO2ZWUudpFNyPN7EPFYwt7SCvWprOqw8a9b3wO2d56HczEOD0FMm
	 yFacMonEaAxwu1hyUIu58tKJ397HNLvt4zks8Hhs=
From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109849] suboptimal code for vector walking loop
Date: Tue, 21 Nov 2023 14:17:51 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: cvs-commit at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-109849-4-wWXC6NfVvc@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-109849-4@http.gcc.gnu.org/bugzilla/>
References: <bug-109849-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109849

--- Comment #22 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jan Hubicka <hubicka@gcc.gnu.org>:

https://gcc.gnu.org/g:1d82fc2e6824bf83159389729c31a942f7b91b04

commit r14-5679-g1d82fc2e6824bf83159389729c31a942f7b91b04
Author: Jan Hubicka <jh@suse.cz>
Date:   Tue Nov 21 15:17:16 2023 +0100

    optimize std::vector::push_back

    this patch speeds up the push_back at -O3 significantly by making the
    reallocation to be inlined by default.  _M_realloc_insert is general
    insertion that takes iterator pointing to location where the value
    should be inserted.  As such it contains code to move other entries aro=
und
    that is quite large.

    Since appending to the end of array is common operation, I think we sho=
uld
    have specialized code for that.  Sadly it is really hard to work out th=
is
    from IPA passes, since we basically care whether the iterator points to
    the same place as the end pointer, which are both passed by reference.
    This is inter-procedural value numbering that is quite out of reach.

    I also added extra check making it clear that the new length of the vec=
tor
    is non-zero.  This saves extra conditionals.  Again it is quite hard ca=
se
    since _M_check_len seem to be able to return 0 if its parameter is 0.
    This never happens here, but we are not able to propagate this early nor
    at IPA stage.

    libstdc++-v3/ChangeLog:

            PR libstdc++/110287
            PR middle-end/109811
            PR middle-end/109849
            * include/bits/stl_vector.h (_M_realloc_append): New member
function.
            (push_back): Use it.
            * include/bits/vector.tcc: (emplace_back): Use it.
            (_M_realloc_insert): Let compiler know that new vector size is
non-zero.
            (_M_realloc_append): New member function.=