On Sat, 19 Nov 2011 12:01:50 +0200 Gleb Kurtsou <gleb.kurt...@gmail.com> mentioned:
> 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. > Hi! I'm not sure this is relevant to your case, but our base gcc used to have a bug with strict aliasing, which was fixed only in a GPLv3 version of it. That's why we have -fno-strict-aliasing in default CFALGS. So you might try to build using -fno-strict-aliasing. -- Stanislav Sedov ST4096-RIPE () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments
pgpuO922JsvHw.pgp
Description: PGP signature
