From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: [Emacs-diffs] master 74f54af: Use eassume (false) for branch that's never taken. Date: Fri, 19 Apr 2019 12:04:51 -0700 Organization: UCLA Computer Science Department Message-ID: <9b3a1717-64de-795a-2acf-0698576caf02@cs.ucla.edu> References: <83ftqecrms.fsf@gnu.org> <83ef5ycnny.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="85499"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 Cc: phst@google.com, emacs-devel@gnu.org To: Eli Zaretskii , Philipp Stephani Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Apr 19 21:17:24 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1hHZ0m-000M4U-3O for ged-emacs-devel@m.gmane.org; Fri, 19 Apr 2019 21:17:24 +0200 Original-Received: from localhost ([127.0.0.1]:60329 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHZ0k-0008QT-VU for ged-emacs-devel@m.gmane.org; Fri, 19 Apr 2019 15:17:23 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:58442) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHZ0T-00089n-3A for emacs-devel@gnu.org; Fri, 19 Apr 2019 15:17:06 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hHYoi-0003OU-J0 for emacs-devel@gnu.org; Fri, 19 Apr 2019 15:04:57 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:41424) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hHYog-0003Nk-0f; Fri, 19 Apr 2019 15:04:54 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id D828A161774; Fri, 19 Apr 2019 12:04:52 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id hHr0Rgn9RJzE; Fri, 19 Apr 2019 12:04:52 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 1823216179A; Fri, 19 Apr 2019 12:04:52 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id WAhVSUTN6s50; Fri, 19 Apr 2019 12:04:51 -0700 (PDT) Original-Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id ECCBC160E4A; Fri, 19 Apr 2019 12:04:51 -0700 (PDT) Openpgp: preference=signencrypt Autocrypt: addr=eggert@cs.ucla.edu; prefer-encrypt=mutual; keydata= xsFNBEyAcmQBEADAAyH2xoTu7ppG5D3a8FMZEon74dCvc4+q1XA2J2tBy2pwaTqfhpxxdGA9 Jj50UJ3PD4bSUEgN8tLZ0san47l5XTAFLi2456ciSl5m8sKaHlGdt9XmAAtmXqeZVIYX/UFS 96fDzf4xhEmm/y7LbYEPQdUdxu47xA5KhTYp5bltF3WYDz1Ygd7gx07Auwp7iw7eNvnoDTAl KAl8KYDZzbDNCQGEbpY3efZIvPdeI+FWQN4W+kghy+P6au6PrIIhYraeua7XDdb2LS1en3Ss mE3QjqfRqI/A2ue8JMwsvXe/WK38Ezs6x74iTaqI3AFH6ilAhDqpMnd/msSESNFt76DiO1ZK QMr9amVPknjfPmJISqdhgB1DlEdw34sROf6V8mZw0xfqT6PKE46LcFefzs0kbg4GORf8vjG2 Sf1tk5eU8MBiyN/bZ03bKNjNYMpODDQQwuP84kYLkX2wBxxMAhBxwbDVZudzxDZJ1C2VXujC OJVxq2kljBM9ETYuUGqd75AW2LXrLw6+MuIsHFAYAgRr7+KcwDgBAfwhPBYX34nSSiHlmLC+ KaHLeCLF5ZI2vKm3HEeCTtlOg7xZEONgwzL+fdKo+D6SoC8RRxJKs8a3sVfI4t6CnrQzvJbB n6gxdgCu5i29J1QCYrCYvql2UyFPAK+do99/1jOXT4m2836j1wARAQABzSBQYXVsIEVnZ2Vy dCA8ZWdnZXJ0QGNzLnVjbGEuZWR1PsLBfgQTAQIAKAUCTIByZAIbAwUJEswDAAYLCQgHAwIG FQgCCQoLBBYCAwECH In-Reply-To: <83ef5ycnny.fsf@gnu.org> Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 131.179.128.68 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:235670 Archived-At: On 4/19/19 3:08 AM, Eli Zaretskii wrote: > When ENABLE_CHECKING is not defined, which happens in every production > build, eassume expands to code that has no side effects, so the > function will return a random value to its caller. I don't think this > is desired. It looks OK to me. The default branch is impossible, so the function cannot return a random value to its caller. Although GCC is not smart enough to deduce this fact, eassume lets the programmer communicate it to GCC so that GCC doesn't issue a false-alarm diagnostic (and GCC also can generate better code). When ENABLE_CHECKING is defined, there's also a runtime check that the impossible does not happen, but this extra check isn't needed in ordinary production. This would all be simpler if we replaced 'enum nonlocal_exit' with a simple boolean. The enum seems to be more trouble than it's worth, if it's causing this sort of bikeshedding. Not every boolean deserves an enum just for it.