#6 Failure when compiled with optimization

[Louis Krupp]

From [https://unix.stackexchange.com/questions/609693/feeding-a-command-using-file-redirection-or-pipe-doesnt-always-work/610101#610101]:

Summary: The program fails intermittently when compiled by certain versions of gfortran at certain optimization levels, and it's not immediately clear if the problem is with the program or with the compiler.

Answer contributed by posters to comp.lang.fortran:

One problem seems to be where the main loop:

~~~
done = .false.
do while (.not. done)

call main_menu(command)
call run_command(command, surf, options, done, ioerror)

end do

calls 'run_command':

subroutine run_command(command, surf, options, done, ioerror)
...
logical, intent(out) :: done
integer, intent(inout) :: ioerror

gfortran seems to be guessing that since the value of 'done' is never used by 'run_command', there's no point in actually executing the statement `done = .false`. and since 'run_command' doesn't actually set its argument 'done' to anything unless it sees a 'quit' command, 'done' is left uninitialized when the main loop checks it. Sometimes it's false, and sometimes it contains garbage, in which case it's evaluated as true and the main loop terminates early.

Changing the intent of 'done' to 'inout' seems to fix the problem.

Setting 'done' before the 'select case' statement in run_command also seems to work:

done = .false.

select case (command)
...
~~~

My guess is that this is the right way to fix this, and that the compiler's behavior, while surprising to some of us (including me), is in fact correct.

valgrind helped find this.

And from another poster:

Along the same lines, the several instances of

type(options_type), intent(out) :: opt

in file menu.f90 should be changed to

type(options_type), intent(inout) :: opt

or the intent clause should be left out, because an argument with intent(out) becomes undefined when the subprogram is entered and stays undefined unless it acquires a value in the subprogram before returning.

Other suggestions included compiling and running with options to check array bounds, etc.

[Louis Krupp]

Another attempt at the StackExchange link: https://unix.stackexchange.com/questions/609693/feeding-a-command-using-file-redirection-or-pipe-doesnt-always-work/610101#610101