From owner-freebsd-hackers@FreeBSD.ORG Sat Nov 19 17:11:04 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 D0D661065674 for ; Sat, 19 Nov 2011 17:11:04 +0000 (UTC) (envelope-from mdf356@gmail.com) Received: from mail-yw0-f54.google.com (mail-yw0-f54.google.com [209.85.213.54]) by mx1.freebsd.org (Postfix) with ESMTP id 8EA848FC14 for ; Sat, 19 Nov 2011 17:11:04 +0000 (UTC) Received: by ywe9 with SMTP id 9so5125092ywe.13 for ; Sat, 19 Nov 2011 09:11:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=T1T/drm0jNnTXxdlU/U5pwJK54NQm/G/b8u848NCcLE=; b=m1SGxdn00bCXrhaWQuUsgmkw9ixGU+KV5Z5KFH1dO4GrCk0+rJceZI98eWUff4kQfw n7qHLYx69HEDKwjCcNV9pR44F75zXwRL+W+9Ic3cYO9E2vv9I+IIp+MGbVxMuWCh7Foj NnRx+KMa/eH36aGhTnu9hCRu9t0rwmNrz4eDI= MIME-Version: 1.0 Received: by 10.68.21.162 with SMTP id w2mr15823386pbe.25.1321722663368; Sat, 19 Nov 2011 09:11:03 -0800 (PST) Sender: mdf356@gmail.com Received: by 10.68.56.97 with HTTP; Sat, 19 Nov 2011 09:11:03 -0800 (PST) In-Reply-To: <20111119161958.GA91681@reks> References: <20111119100150.GA1560@reks> <20111119161958.GA91681@reks> Date: Sat, 19 Nov 2011 09:11:03 -0800 X-Google-Sender-Auth: gYP-nPg9s9Dsp1WsEOcNEa2xOyQ Message-ID: From: mdf@FreeBSD.org To: Gleb Kurtsou Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 17:11:05 -0000 On Sat, Nov 19, 2011 at 8:19 AM, Gleb Kurtsou wrot= e: > On (19/11/2011 07:26), mdf@FreeBSD.org wrote: >> On Sat, Nov 19, 2011 at 2:01 AM, Gleb Kurtsou w= rote: >> > 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 g= cc >> > 4.3, gcc 4.4 on FreeBSD and Linux. Clang from base is also good. -O an= d >> > -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 inlin= ed >> > assertion functions. gcc fails to correctly optimize struct assignment= s >> > with -fno-omit-frame-pointer, I have a number of small structs assigne= d, >> > 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? =A0gcc 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. =A0I 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. I can't find the thing I'm thinking of. The only potentially relevant patch I see in our gcc sources is this: Index: opts.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- opts.c (.../vendor.branches/freebsd/stable/7/src/contrib/gcc/opts.c) (r= evision 211574) +++ opts.c (.../head/src/contrib/gcc/opts.c) (revision 211574) @@ -457,11 +457,7 @@ flag_tree_dse =3D 1; flag_tree_ter =3D 1; flag_tree_live_range_split =3D 1; + /** + * 7dot1MERGE: tree-sra in gcc 4.2.x is buggy and + * breaks bitfield structs. + */ + flag_tree_sra =3D 0; - flag_tree_sra =3D 1; flag_tree_copyrename =3D 1; flag_tree_fre =3D 1; flag_tree_copy_prop =3D 1; Thanks, matthew