[Bug fortran/91359] logical function X returns .TRUE. - Warning: spaghetti code

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91359

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-08-05
                 CC|                            |kargl at gcc dot gnu.org
            Summary|GFORTRAN [NNNNN RETURN]  of |logical function X returns
                   |.FALSE. logical function X  |.TRUE. - Warning:
                   |returns .TRUE. after [if    |spaghetti code
                   |(.not.X) goto NNNNN] -      |
                   |Warning:  spaghetti code    |
     Ever confirmed|0                           |1

--- Comment #1 from kargl at gcc dot gnu.org ---
The options -finit-local-zero and -fno-automatic are unimportant.

Compiling the code in comment #1 with -fdump-tree-original reveals
the problem as the function is translated into 

zero ()
{
  logical(kind=4) __result_zero;

  goto __label_000002;
  __label_000001:;
  return;
  __label_000002:;
  __result_zero = 0;
  if (!__result_zero) goto __label_000001;
  L.1:;
  return __result_zero;
  return __result_zero;
}

Notice the first 'return' statement has no value to return.
A work around to to introduce a RESULT variable.  This is
translated to

      function zero() result(a)
         logical a
         goto 2
1        return
2        a = .false.
         if (.not. a) goto 1
         return
      end

zero ()
{
  logical(kind=4) a;

  goto __label_000002;
  __label_000001:;
  return a;
  __label_000002:;
  a = 0;
  if (!a) goto __label_000001;
  L.1:;
  return a;
  return a;
}