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 976FE3858D33; Mon, 16 Jan 2023 13:14:23 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 976FE3858D33
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1673874863;
	bh=tjFa4++N3Jtcd90gRadKh0GK+MBzkMliAToYCLkHHFA=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=ph17laDHLFEzONhwmo4VAWAIig94yln6SooaQewIzyHYj+OG1b0ziXNC4+ak4qyQI
	 Ddh87UnhCI91X/TNlAo4idZbsg0yoBcydpwpZ++1cBjD6awpcqbTBzxZrTyMP381Oz
	 GUL83X1tzgAP+U8pGb/df9p9MroVWeG8rSx9fyJg=
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106093] [12/13 Regression] False positive
 -Wstringop-overflow with -O3 when resizing std::vector
Date: Mon, 16 Jan 2023 13:14:23 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.1.0
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 12.3
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-106093-4-KJzlrQIREN@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-106093-4@http.gcc.gnu.org/bugzilla/>
References: <bug-106093-4@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=3D106093

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> in particular the new allocated storage is processed but the old size is
> used?!

Yes, that seems correct.

We're resizing the vector from N to N+1 (where N happens to be 0). The new =
size
is greater than the existing capacity, so we allocate N+1 elements, then co=
py
the existing N elements into the new storage (which uses old_finish -
old_start).

Afterwards, we would actually construct the new element in the new storage,=
 but
the warning happens while just copying the elements from the old storage to=
 the
new.=