$cat test.f90
program test
real :: foo
contains
    function foo ()
    end function foo
end program test

Gfortran passes it.

If add external attribute, we'll get ICE.

$cat test2.f90
program test
real, external :: foo
contains
    function foo ()
    end function foo
end program test
$gfortran test2.f90
test2.f90: In function ‘MAIN__â€?
test2.f90:7: internal compiler error: in build_function_decl, at fortran/trans
-decl.c:1063
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
$gfortran -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../gcc/configure --enable-languages=c,fortran
--prefix=/home/wf
/local : (reconfigured) ../gcc/configure --prefix=/home/wf/local
--enable-langua
ges=c,fortran --no-create --no-recursion : (reconfigured) ../gcc/configure
--pre
fix=/home/wf/local --enable-languages=c,fortran --no-create --no-recursion
Thread model: posix
gcc version 4.1.0 20051010 (experimental)


-- 
           Summary: Does not detect duplicate symbol names in contains block
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: ice-on-invalid-code, accepts-invalid
          Severity: normal
          Priority: P2
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: fengwang at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24327