[gcc r11-3301] Work around bootstrap failure in Fortran front end.

[gcc r11-3301] Work around bootstrap failure in Fortran front end.

[Sandra Loosemore]

https://gcc.gnu.org/g:a85e5696a31cac8c14dde14f031e76480205f8a0

commit r11-3301-ga85e5696a31cac8c14dde14f031e76480205f8a0
Author: Sandra Loosemore <sandra@codesourcery.com>
Date:   Sat Sep 19 07:32:35 2020 -0700

    Work around bootstrap failure in Fortran front end.
    
    Switching the C++ front end to lower loops the same was as the C front
    end triggered this error when bootstrapping the Fortran front end:
    
    /path/to/gcc/fortran/interface.c:3546:12: error: '*new_arg' may be used uninitialized [-Werror=maybe-uninitialized]
     3546 |   new_arg[i]->next = NULL;
          |   ~~~~~~~~~^
    
    Work around this by adding an assertion, which seems appropriate for
    documentation and good coding practices anyway.
    
    2020-08-12  Sandra Loosemore  <sandra@codesourcery.com>
    
            gcc/fortran/
            * interface.c (gfc_compare_actual_formal): Add assertion after
            main processing loop to silence maybe-uninitialized error.

Diff:
---
 gcc/fortran/interface.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/fortran/interface.c b/gcc/fortran/interface.c
index 020cdd73df8..e2cc76f0024 100644
--- a/gcc/fortran/interface.c
+++ b/gcc/fortran/interface.c
@@ -3530,6 +3530,10 @@ gfc_compare_actual_formal (gfc_actual_arglist **ap, gfc_formal_arglist *formal,
 	}
     }
 
+  /* We should have handled the cases where the formal arglist is null
+     already.  */
+  gcc_assert (n > 0);
+
   /* The argument lists are compatible.  We now relink a new actual
      argument list with null arguments in the right places.  The head
      of the list remains the head.  */