From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 7A1DD3858C2C; Mon, 3 Jan 2022 09:09:11 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 7A1DD3858C2C From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/102043] Wrong array types used for negative stride accesses Date: Mon, 03 Jan 2022 09:09:11 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: fortran X-Bugzilla-Version: 12.0 X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenth 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: 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: Mon, 03 Jan 2022 09:09:11 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102043 --- Comment #31 from Richard Biener --- (In reply to Mikael Morin from comment #28) > I=E2=80=99m reading the previous comments again: >=20 > (In reply to Richard Biener from comment #10) > > So to clarify the ARRAY_REF constraints - there is currently no way to > > construct a valid ARRAY_REF where an index does an access to memory bef= ore > > the supplied > > base object. TREE_OPERAND (array_ref, 0) needs to always be the array, > > it's address needs to be the address of the _first_ element. For negat= ive > > strides gfortran seems to construct the array object in a way so its > > address points to the _last_ element of the array. That's not supporte= d. > >=20 > does that means that clearing the lower bound information from the type a= s I > suggested in my last comment would not work? Correct - the lower bound is used to bias 'i' in 'array[i]', the result sti= ll has to be >=3D 0. As said the middle-end lacks support for (negative) stride arrays. For a negative stride array you'd probably expect array[i] to compute &array[ubound - S * i]? That said, the middle-end doesn't even handle positive strided accesses - t= he stride needs to be manually reflected to the index which means that the arr= ay type domain does not really reflect the "true" shape of the array. It's re= ally tied to C language array support (where array accesses are just fancy ways of pointer arithmetic).=