From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 88906 invoked by alias); 2 Dec 2015 08:57:55 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 88851 invoked by uid 89); 2 Dec 2015 08:57:54 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.4 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx2.suse.de Received: from mx2.suse.de (HELO mx2.suse.de) (195.135.220.15) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (CAMELLIA256-SHA encrypted) ESMTPS; Wed, 02 Dec 2015 08:57:53 +0000 Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id A7F5CAAB4; Wed, 2 Dec 2015 08:57:47 +0000 (UTC) Date: Wed, 02 Dec 2015 08:57:00 -0000 From: Richard Biener To: Trevor Saunders cc: tbsaunde+gcc@tbsaunde.org, gcc-patches@gcc.gnu.org, rdsandiford@googlemail.com Subject: Re: [PATCH 1/2] destroy values as well as keys when removing them from hash maps In-Reply-To: <20151202050346.GA29495@tsaunders-iceball.corp.tor1.mozilla.com> Message-ID: References: <1448318933-23235-1-git-send-email-tbsaunde+gcc@tbsaunde.org> <87wpsy3qfs.fsf@googlemail.com> <20151202050346.GA29495@tsaunders-iceball.corp.tor1.mozilla.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SW-Source: 2015-12/txt/msg00205.txt.bz2 On Wed, 2 Dec 2015, Trevor Saunders wrote: > On Tue, Dec 01, 2015 at 07:43:35PM +0000, Richard Sandiford wrote: > > tbsaunde+gcc@tbsaunde.org writes: > > > -template > > > +template > > > template > > > inline void > > > -simple_hashmap_traits ::remove (T &entry) > > > +simple_hashmap_traits ::remove (T &entry) > > > { > > > H::remove (entry.m_key); > > > + entry.m_value.~Value (); > > > } > > > > This is just repeating my IRC comment really, but doesn't this mean that > > we're calling the destructor on an object that was never constructed? > > I.e. nothing ever calls placement new on the entry, the m_key, or the > > m_value. > > I believe you are correct that placement new is not called. I'd say its > a bug waiting to happen given that the usage of auto_vec seems to > demonstrate that people expect objects to be initialized and destroyed. > However for now all values are either POD, or auto_vec and in either > case the current 0 initialization has the same effect as the > constructor. So There may be a theoretical problem with how we > initialize values that will become real when somebody adds a constructor > that doesn't just 0 initialize. So it should probably be improved at > some point, but it doesn't seem necessary to mess with it at this point > instead of next stage 1. Agreed. You'll also need a more elaborate allocator/constructor scheme for this considering the case where no default constructor is available. See how alloc-pool.h tries to dance around this using a "raw" allocate and a operator new... Richard. > Trev > > > > > Thanks, > > Richard > > -- Richard Biener SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)