This is my first report at gcc Bugzilla...

I tried to compile a fortran program that invokes QD library (multiprecision arithmetic, available at http://www.cs.berkeley.edu/~yozo/software/qd-2.3.7.tar.gz). When I use Intel compiler suite, everything is fine. If I switch to gcc (the performance of QD is much better when it is compiled with g++ rather than Intel C++) then I get the following error message:

In file f_main.f90:17

call random_number(s)
                    1
Error: There is no specific subroutine for the generic 'random_number' at (1)
make: *** [f_main.o] Error 1

I have investigated the issue a little it and came to the conclusion that there is something wrong with interfacing in gfortran. The QD library has fortran modules called ddmod.f90 and qdmod.f90 which contain the following:

  interface random_number
    module procedure ddrand
  end interface

  interface random_number
    module procedure qdrand
  end interface

random_number is interfaced to allow it to be called with the types or real numbers implemented in QD [type(qd_real) and type(dd_real)]. But in my code I want to call random_number with standard real(8) type. Intel fortran has no problems with it, the compilation goes fine and the program runs as expected. So there must be a bug in gfortran.

In order to make things work I simply removed those interfaces from qdmod.f90 and ddmod.f90 (I don't need random_number with type(qd_real) and type(dd_real) anyway). After doing that everything goes fine.