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* [Bug tree-optimization/60229] New: wrong code at -O2 and -O3 on x86_64-linux-gnu @ 2014-02-16 20:28 su at cs dot ucdavis.edu 2014-02-16 23:09 ` [Bug tree-optimization/60229] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: su at cs dot ucdavis.edu @ 2014-02-16 20:28 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60229 Bug ID: 60229 Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu Product: gcc Version: 4.7.4 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: su at cs dot ucdavis.edu The latest gcc 4.7 branch miscompiles the following code on x86_64-linux at -O2 and -O3 in both 32-bit and 64-bit modes. It also affects 4.6.x, but not 4.8.x and the current gcc trunk. The issue seems to be considering signed short and signed char for overflows, but neither overflows. $ gcc-trunk -O2 small.c $ a.out $ gcc-4.8.2 -O2 small.c $ a.out $ gcc-4.7.3 -O2 small.c $ a.out ^C $ gcc-4.7-branch -O2 small.c $ a.out ^C $ gcc-4.7-branch -v Using built-in specs. COLLECT_GCC=gcc-4.7-branch COLLECT_LTO_WRAPPER=/usr/local/gcc47-branch/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.7.4/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-4.7/configure --enable-languages=c,c++ Thread model: posix gcc version 4.7.4 20140209 (prerelease) [gcc-4_7-branch revision 207641] (GCC) $ ------------------- short a; int main() { for (; a >= 0; a++) ; return 0; } ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/60229] wrong code at -O2 and -O3 on x86_64-linux-gnu 2014-02-16 20:28 [Bug tree-optimization/60229] New: wrong code at -O2 and -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu @ 2014-02-16 23:09 ` pinskia at gcc dot gnu.org 2014-02-16 23:10 ` pinskia at gcc dot gnu.org 2014-02-17 9:54 ` jakub at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2014-02-16 23:09 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60229 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |DUPLICATE --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Dup of bug 35634. *** This bug has been marked as a duplicate of bug 35634 *** ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/60229] wrong code at -O2 and -O3 on x86_64-linux-gnu 2014-02-16 20:28 [Bug tree-optimization/60229] New: wrong code at -O2 and -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu 2014-02-16 23:09 ` [Bug tree-optimization/60229] " pinskia at gcc dot gnu.org @ 2014-02-16 23:10 ` pinskia at gcc dot gnu.org 2014-02-17 9:54 ` jakub at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2014-02-16 23:10 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60229 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Note there is no overflow happening here at all. In that a++ is the same as a = a + 1 which is the same as a = (short)(((int)a) + 1) due to promotion rules in C. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/60229] wrong code at -O2 and -O3 on x86_64-linux-gnu 2014-02-16 20:28 [Bug tree-optimization/60229] New: wrong code at -O2 and -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu 2014-02-16 23:09 ` [Bug tree-optimization/60229] " pinskia at gcc dot gnu.org 2014-02-16 23:10 ` pinskia at gcc dot gnu.org @ 2014-02-17 9:54 ` jakub at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: jakub at gcc dot gnu.org @ 2014-02-17 9:54 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60229 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jakub at gcc dot gnu.org --- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Well, the conversion is implementation-defined behavior, and GCC documents what it does in that case (does it?) and thus you can rely on it, and given that other compilers also have simimilar implementation-defined behavior choice for that case, you can portably assume it unless you are targetting extinct architectures. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2014-02-17 9:54 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2014-02-16 20:28 [Bug tree-optimization/60229] New: wrong code at -O2 and -O3 on x86_64-linux-gnu su at cs dot ucdavis.edu 2014-02-16 23:09 ` [Bug tree-optimization/60229] " pinskia at gcc dot gnu.org 2014-02-16 23:10 ` pinskia at gcc dot gnu.org 2014-02-17 9:54 ` jakub at gcc dot gnu.org
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