[Bug fortran/56872] New: Incorrect SUM evaluation, involving implied-do loop, with -ffrontend-optimize

[townsend at astro dot wisc.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56872



             Bug #: 56872

           Summary: Incorrect SUM evaluation, involving implied-do loop,

                    with -ffrontend-optimize

    Classification: Unclassified

           Product: gcc

           Version: 4.9.0

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: fortran

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: towns...@astro.wisc.edu





The attached code gives the incorrect results when compiled with

-ffrontend-optimize (either explicitly, or via use of one of the -O flags).



Correct behavior:



$ gfortran -o sum_bug sum_bug.f90

$ ./sum_bug 

   1.00000000       1000.00000    

   1001.00000    



Incorrect behavior (i):



$ gfortran -O2 -o sum_bug sum_bug.f90

$ ./sum_bug 

   1.00000000       1000.00000    

   1.00000005E-03



Incorrect behavior (ii):



$ gfortran -ffrontend-optimize -o sum_bug sum_bug.f90

$ ./sum_bug 

   1.00000000       1000.00000    

         Infinity



gfortran -v gives:



Using built-in specs.

COLLECT_GCC=/Applications/madsdk/bin/gfortran.exec

COLLECT_LTO_WRAPPER=/Applications/madsdk/libexec/gcc/x86_64-apple-darwin11.4.2/4.9.0/lto-wrapper

Target: x86_64-apple-darwin11.4.2

Configured with: ./configure CC='gcc -D_FORTIFY_SOURCE=0'

--build=x86_64-apple-darwin11.4.2 --prefix=/Applications/madsdk

--with-gmp=/Applications/madsdk --with-mpfr=/Applications/madsdk

--with-mpc=/Applications/madsdk --enable-languages=c,c++,fortran

--disable-multilib

Thread model: posix

gcc version 4.9.0 20130404 (experimental) (GCC)