From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Conservative GC isn't safe Date: Mon, 28 Nov 2016 19:57:19 +0200 Message-ID: <83a8cjzdvk.fsf@gnu.org> References: <66485157-00cd-4704-a421-cbfe84299cae@cs.ucla.edu> <805F5A19-BFAF-4CA4-AAD6-497C6D554830@raeburn.org> <6e5c928f-8130-08a6-d72d-1b64cc022846@cs.ucla.edu> <1CB11DFF-E6C2-4A1B-BE7E-8877DC38DB0A@raeburn.org> <83inr7zjjf.fsf@gnu.org> <83bmwzzet5.fsf@gnu.org> Reply-To: Eli Zaretskii NNTP-Posting-Host: blaine.gmane.org X-Trace: blaine.gmane.org 1480355851 10829 195.159.176.226 (28 Nov 2016 17:57:31 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 28 Nov 2016 17:57:31 +0000 (UTC) Cc: emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon Nov 28 18:57:28 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cBQBE-00022X-9O for ged-emacs-devel@m.gmane.org; Mon, 28 Nov 2016 18:57:28 +0100 Original-Received: from localhost ([::1]:60401 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBQBH-0005t4-RH for ged-emacs-devel@m.gmane.org; Mon, 28 Nov 2016 12:57:31 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:55006) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBQBB-0005sn-7Z for emacs-devel@gnu.org; Mon, 28 Nov 2016 12:57:25 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cBQB8-0001Eo-6J for emacs-devel@gnu.org; Mon, 28 Nov 2016 12:57:25 -0500 Original-Received: from fencepost.gnu.org ([2001:4830:134:3::e]:46008) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBQB8-0001Ek-3K; Mon, 28 Nov 2016 12:57:22 -0500 Original-Received: from 84.94.185.246.cable.012.net.il ([84.94.185.246]:3595 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1cBQB7-0000QS-Bl; Mon, 28 Nov 2016 12:57:21 -0500 In-reply-to: (message from Stefan Monnier on Mon, 28 Nov 2016 12:49:28 -0500) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:4830:134:3::e X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:209659 Archived-At: > From: Stefan Monnier > Date: Mon, 28 Nov 2016 12:49:28 -0500 > > >> >> res = Fvector (ito - ifrom, aref_addr (string, ifrom)); > >> > But 'string' still references the contents array of the vector, so GC > >> > will mark it when it comes to 'string'. > >> But after computing "aref_addr (string, ifrom)", it may very well be > >> that `string` is dead and the compiler may then decide not to write > >> it into the stack. > > It will still be there in the caller. > > Only if the caller still needs it after the call. > That's usually the case, but it's not a given. If it is not needed after the call, it will be clobbered after the call, but not during the call.