http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59168
Bug ID: 59168 Summary: Wrong result with non-optimized (!) compilation Product: gcc Version: 4.8.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran Assignee: unassigned at gcc dot gnu.org Reporter: sarantis.pantazis at gmail dot com I wanted to check the difference in CPU time in the calculation of a sum when the terms are included in the same expression and when they are added separately. For this reason I wrote the attached code. First I compiled with "gfortran -o test testPartialSum.f08" and got the following results: 199204048. 67108864.0 0.117000006 0.244000003 Then I compiled with "gfortran -o test testPartialSum.f08 -O3" and got the following results: 200000000. 200000000. 7.80000016E-02 7.50000030E-02 It seems clear that the optimized compilation provides the correct results but the non-optimized one does not (which seems very weird to me!!!). >uname -a Linux i75454 3.7.10-1.16-desktop #1 SMP PREEMPT Fri May 31 20:21:23 UTC 2013 (97c14ba) i686 i686 i386 GNU/Linux >cat /etc/issue Welcome to openSUSE 12.3 "Dartmouth" - Kernel \r (\l). >gfortran -v Using built-in specs. COLLECT_GCC=gfortran COLLECT_LTO_WRAPPER=/home/myUserame/gcc-latest/gcc-4.8.2/lib/gcc/i686-pc-linux-gnu/4.8.2/lto-wrapper Target: i686-pc-linux-gnu Configured with: ../configure --prefix=/home/myUsername/gcc-latest/gcc-4.8.2 --enable-languages=c,fortran,c++ Thread model: posix gcc version 4.8.2 (GCC)