[Bug c/50254] gcc-4.5 -fstrict-aliasing -fschedule-insns optimization produces wrong code
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50254 Vladimir Zapolskiy changed: What|Removed |Added Status|RESOLVED|CLOSED --- Comment #3 from Vladimir Zapolskiy 2011-09-01 09:37:33 UTC --- Closed, thanks.
[Bug c/50254] gcc-4.5 -fstrict-aliasing -fschedule-insns optimization produces wrong code
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50254
Vladimir Zapolskiy changed:
What|Removed |Added
Attachment #25154|0 |1
is obsolete||
--- Comment #2 from Vladimir Zapolskiy 2011-09-01
09:37:00 UTC ---
Created attachment 25157
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25157
test code
(In reply to comment #1)
> qentry->next = (void *)qhead;
>
> is voiolating strict aliasing rules if you ever end up loading/storing
> qentry->next->{prev,next}.
Thank you very much for the quick response.
I managed to reduce a test case and hopefully understand strict aliasing rules.
[Bug c/50254] New: gcc-4.5 -fstrict-aliasing -fschedule-insns optimization produces wrong code
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50254 Bug #: 50254 Summary: gcc-4.5 -fstrict-aliasing -fschedule-insns optimization produces wrong code Classification: Unclassified Product: gcc Version: 4.5.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassig...@gcc.gnu.org ReportedBy: vzapols...@gmail.com Created attachment 25154 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25154 test code Hello, recently my team found a problem in our code after a gcc compiler update from gcc-4.4 to gcc-4.5. I've extracted the problematic code snippet, you can find it in the attachement. The problem is unveiled, if you try to compile the test with various combinations of base optimization and strict-aliasing and fschedule-insns flags. For instance that's what I get on my amd64/gcc-4.6.0: $ gcc -O0 test.c -o test && ./test $ gcc -O0 -fschedule-insnstest.c -o test && ./test $ gcc -O0 -fstrict-aliasingtest.c -o test && ./test $ gcc -O0 -fstrict-aliasing-fschedule-insnstest.c -o test && ./test Aborted $ gcc -O1 test.c -o test && ./test $ gcc -O1 -fschedule-insnstest.c -o test && ./test $ gcc -O1 -fstrict-aliasingtest.c -o test && ./test Aborted $ gcc -O1 -fstrict-aliasing-fschedule-insnstest.c -o test && ./test Aborted $ gcc -O2 test.c -o test && ./test Aborted $ gcc -O2 -fno-strict-aliasing test.c -o test && ./test $ gcc -O2 -fno-schedule-insns test.c -o test && ./test Aborted $ gcc -O2 -fno-strict-aliasing -fno-schedule-insns test.c -o test && ./test $ The problem described above is reproducible on armv7, i386, amd64 target architectures with gcc-4.5 and gcc-4.6 compilers. The issue might be invalid, but because it hasn't been known with gcc-4.4, I'd greatly appreciate to get some comments from GCC team on it. Thank you in advance.
[Bug libstdc++/39238] trunk revision 144279 - cfenv:54: error: �::fenv_t� has not been declared
--- Comment #10 from vzapolskiy at gmail dot com 2009-08-27 16:00 --- I have encountered the same problem with reverse cross compilation of gcc-4.3 branch on Linux for powerpc target. The problem was introduced in #38000 (revision 143194), and safe solution is just to revert the changes on the next files: * libstdc++-v3/include/c_global/cfenv * libstdc++-v3/include/tr1/cfenv * libstdc++-v3/include/tr1_impl/cfenv * libstdc++-v3/include/c_compatibility/fenv.h Proposed patch for gcc-4_4-branch (revision 151142) is attached. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39238
[Bug libstdc++/39238] trunk revision 144279 - cfenv:54: error: �::fenv_t� has not been declared
--- Comment #9 from vzapolskiy at gmail dot com 2009-08-27 15:59 --- Created an attachment (id=18438) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18438&action=view) proposed patch for the problem resolution on gcc-4_4-branch -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39238
