From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 4522F385800A; Wed, 1 Dec 2021 16:22:42 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4522F385800A From: "aldyh at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/101912] -Wmaybe-uninitialized false alarm in tzdb localtime.c Date: Wed, 01 Dec 2021 16:22:42 +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: 11.2.1 X-Bugzilla-Keywords: diagnostic X-Bugzilla-Severity: normal X-Bugzilla-Who: aldyh 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: cc Message-ID: In-Reply-To: References: 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 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 01 Dec 2021 16:22:42 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101912 Aldy Hernandez changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |law at gcc dot gnu.org --- Comment #6 from Aldy Hernandez --- (In reply to rguenther@suse.de from comment #5) > On Tue, 30 Nov 2021, eggert at cs dot ucla.edu wrote: >=20 > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101912 > >=20 > > --- Comment #4 from eggert at cs dot ucla.edu --- > > (In reply to Aldy Hernandez from comment #3) > > > > && !(leapcnt =3D=3D 0 > > > > || (prevcorr < corr > > > > ? corr =3D=3D prevcorr + 1 > > > > : (corr =3D=3D prevcorr > > > > || corr =3D=3D prevcorr - 1))))) > > > >=20 > > >=20 > > > I guess the question is whether language rules allow us to read prevc= orr > > > when leapcnt=3D=3D 0? > >=20 > > The C language rules do not allow that. When leapcnt is zero, behavior = must be > > as if the prevcorr expression is not evaluated. > >=20 > > Although the compiler can generate machine code that evaluates prevcorr= at the > > machine level (so long as the observable behavior is the same, which is= the > > case as prevcorr is not volatile and no untoward behavior can result fr= om > > evaluating the prevcorr expression), it's incorrect if the compiler war= ns the > > programmer that prevcorr is used uninitialized. >=20 > Correct. I think we have quite some duplicates around this issue > of making short-circuiting conditionals not short-circuiting (we do > that even early during GENERIC folding). "Proving" that all participating > sub-expressions are fully initialized is impossible so the only > reasonable way to "fix" the issue (the uninit warnings) might be > to mark the now unconditionally evaluated sub-expressions with > -Wno-uninitialized (aka no-warning or suppress uninit warnings). If this isn't something we are going to fix then by all means, mark them al= l as -Wno-uninitialized. I'm for whatever reduces the false positive rates in t= his area :).=