From owner-freebsd-hackers@FreeBSD.ORG Sat Nov 19 16:20:01 2011 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id CCCFE1065670; Sat, 19 Nov 2011 16:20:01 +0000 (UTC) (envelope-from gleb.kurtsou@gmail.com) Received: from mail-bw0-f54.google.com (mail-bw0-f54.google.com [209.85.214.54]) by mx1.freebsd.org (Postfix) with ESMTP id 2A63A8FC12; Sat, 19 Nov 2011 16:20:00 +0000 (UTC) Received: by bkbzs8 with SMTP id zs8so6321073bkb.13 for ; Sat, 19 Nov 2011 08:20:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=runb1jEGd8Qg8JOmiu2GJphSi7GojDIU3zyj4QWUfyU=; b=sc/5znHrvgqU23LXtubfEihdGtp8cUTUd2MOXxEH9tyWYFeeWGQm0I7JtKBeKRN/6a 3YQgbfYAck+7+7eFmJoLCNuE49mYjmcKGPprsJbKlIntwzvFMfmgnVRlV4w8XurkqDNJ 6zY9nYjPMdxBdwA+rISO3VBrLvhlnGt25zYBo= Received: by 10.205.126.13 with SMTP id gu13mr7840081bkc.114.1321719600123; Sat, 19 Nov 2011 08:20:00 -0800 (PST) Received: from localhost ([78.157.92.5]) by mx.google.com with ESMTPS id o7sm3204331bkw.16.2011.11.19.08.19.58 (version=SSLv3 cipher=OTHER); Sat, 19 Nov 2011 08:19:58 -0800 (PST) Date: Sat, 19 Nov 2011 18:19:59 +0200 From: Gleb Kurtsou To: mdf@FreeBSD.org Message-ID: <20111119161958.GA91681@reks> References: <20111119100150.GA1560@reks> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Cc: freebsd-hackers@freebsd.org Subject: Re: gcc 4.2 miscompilation with -O2 -fno-omit-frame-pointer on amd64 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 19 Nov 2011 16:20:01 -0000 On (19/11/2011 07:26), mdf@FreeBSD.org wrote: > On Sat, Nov 19, 2011 at 2:01 AM, Gleb Kurtsou wrote: > > Hi, > > > > I was lucky to write a bit of code which gcc 4.2 fails to compile > > correctly with -O2. Too keep long story short the code fails for gcc > > from base system and last gcc 4.2 snapshot from ports. It works with gcc > > 4.3, gcc 4.4 on FreeBSD and Linux. Clang from base is also good. -O and > > -Os optimization levels are fine (I've tried with all -f* flags > > mentioned in documentation) > > > > -O2 -fno-omit-frame-pointer combination is troublesome on amd64. I > > presume i386 should be fine. These options are also used for > > compilation of kernel (with debugging enabled) and modules. > > > > I'm not able to share the code, but have a test case reproducing the > > bug. I've encountered the issue over a week ago and tried narrowing it down > > to a simple test I could share but without much success. > > > > The code itself is very common: initialize two structs on stack, call a > > function with pointers to those stucts as arguments. A number of inlined > > assertion functions. gcc fails to correctly optimize struct assignments > > with -fno-omit-frame-pointer, I have a number of small structs assigned, > > gcc decides not to use data coping but to assign fields directly. I've > > tried disabling sra, tweaking sra parameters -- no luck in forcing it > > to copy data. Replacing one particular assignment with memcpy produces > > correct code, but that's not a solution. > > How small are the structs? gcc has an optimization for structs that > are no larger than a register, but it's buggy in 4.2 and we disabled > it at $WORK. I can dig up the patch if this is the problem. struct sockaddr_in in this particular test. 16 bytes. Register size structs are rather common, e.g. struct in_addr. I could test the patch. Adding -finline-functions seems to fix the issue for me. Thanks, Gleb. > > Thanks, > matthew