From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 40BF1386103E; Thu, 21 Jan 2021 11:35:56 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 40BF1386103E From: "redi at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/98731] s390x: Large classes of std::bitset and std::vector hash the same Date: Thu, 21 Jan 2021 11:35:55 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Version: 11.0 X-Bugzilla-Keywords: ABI X-Bugzilla-Severity: normal X-Bugzilla-Who: redi at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: redi at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cf_gcctarget keywords 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: Thu, 21 Jan 2021 11:35:56 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98731 Jonathan Wakely changed: What |Removed |Added ---------------------------------------------------------------------------- Target|s390x-linux-gnu |s390x-linux-gnu, | |powerpc-*-*, powerpc64-*-* Keywords| |ABI --- Comment #4 from Jonathan Wakely --- (In reply to Matthias Klose from comment #0) > It appears that the hash value is completely dependent on the size of > the object in bytes. It's not *completely* dependent on the size. Only the last x.size()%64 bits= are hashed incorrectly. For x.size() < 32 it's completely dependent, because we never look at the right bits. For larger numbers of bits we look at *some* = of them. Fixing it is an ABI break though, because it would mean that the same value produces a different hash when compiled with an old GCC or a fixed GCC. Inserting an element into an unordered_map in one TU and then looking it up= in another TU could fail.=