Date: Thu, 8 Dec 2011 13:48:04 -0500 From: Alexander Kabaev <kabaev@gmail.com> To: Gleb Kurtsou <gleb.kurtsou@gmail.com> Cc: freebsd-hackers@FreeBSD.org Subject: Re: gcc 4.2 miscompilation with -O2 -fno-omit-frame-pointer on amd64 Message-ID: <20111208134804.125d45a9@kan.dyndns.org> In-Reply-To: <20111119100150.GA1560@reks> References: <20111119100150.GA1560@reks>
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[-- Attachment #1 --] On Sat, 19 Nov 2011 12:01:50 +0200 Gleb Kurtsou <gleb.kurtsou@gmail.com> 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. > > -O2 -fno-omit-frame-pointer -fno-inline is buggy > -O2 -fno-omit-frame-pointer -frename-registers is buggy > > I found similar issue with gcc 4.6, but I'm not able to reproduce it > with gcc test case: > https://bugzilla.redhat.com/show_bug.cgi?id=679924 > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47893 > > I'll be glad to help debugging it and will be hanging on #bsddev > during weekend as glk. > > > Thanks, > Gleb. > _______________________________________________ It should take about ten times less time than this thread took already to isolate _short_ test case demonstrating the problem, yet nothing of the sort has shown up yet from anyone involved. Am I missing something? -- Alexander Kabaev [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD) iD8DBQFO4QZqQ6z1jMm+XZYRAmjnAJ44tsd9HP911WdQKLpgeKFlY1ESHgCfX19F walqkaEbywO7ZhK3fXIbkNo= =79Kx -----END PGP SIGNATURE-----
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