From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id D25EC3857009; Tue, 1 Dec 2020 16:12:38 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D25EC3857009 From: "msebor at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: =?UTF-8?B?W0J1ZyBjLzk3MTcyXSBbMTEgUmVncmVzc2lvbl0gSUNFOiB0cmVl?= =?UTF-8?B?IGNvZGUg4oCYc3NhX25hbWXigJkgaXMgbm90IHN1cHBvcnRlZCBpbiBMVE8g?= =?UTF-8?B?c3RyZWFtcyBzaW5jZSByMTEtMzMwMy1nNjQ1MGYwNzM4OGY5ZmU1Nw==?= Date: Tue, 01 Dec 2020 16:12:38 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 11.0 X-Bugzilla-Keywords: ice-on-valid-code, lto X-Bugzilla-Severity: normal X-Bugzilla-Who: msebor at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 11.0 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: Tue, 01 Dec 2020 16:12:38 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97172 --- Comment #18 from Martin Sebor --- Let me explain how this works. The VLA bounds in function parameters are u= sed in two ways: 1) in the front end, to check function redeclarations involving arrays and = VLAs for equivalence, 2) in the middle end, to check function calls for out of bounds accesses. As an example of (1) consider the following declarations of function f(): void f (int X, int, int A[X], int B[foo()]); and void f (int, int J, int A[J], int B[foo() + 1]); The bounds in the parameters A and B are different and we'd like them diagnosed. The bound X is the first parameter in the first declaration of f but J is the second parameter in the second f(). Because the bounds are al= so parameters, we use their positions in the argument list to determine that t= hey don't match. Likewise, the bound foo() in B is different from foo() + 1, but because nei= ther is a parameter the only way to determine whether they match is by comparing them for equivalence. The code uses operand_equal_p(..., OEP_LEXICOGRAPHIC= ). (2) is done only for bounds that are parameters. Other bounds are not used= for anything, but they're still stored in the attributes so they can be compare= d in the redeclarations. Since the "complex" bounds aren't used after the front end is done with the= m, unless there's a way to remove them at some point after the front end is do= ne (or set them to NULL or something), the LTO streaming code could ignore them instead of asserting on them. Alternatively, instead of storing them in th= eir tree form they could be stored as strings instead. I list these in the ord= er of my preference for GCC 11.=