Prevent aliasing between arguments in calls to move_alloc

[Paul Richard Thomas]

Dear All,

This patch introduces an error if the to and from arguments of
move_alloc contain the same object or its subobjects. Please see the
comment in the testcase for an explanation and the link to the clf
discussion.

Bootstraps and regtests on FC21/x86_64 - OK for trunk?

Paul

2016-11-05  Paul Thomas  <pault@gcc.gnu.org>

    * check.c (gfc_check_move_alloc): Introduce error to prevent
    aliasing between to and from arguments.

2016-11-05  Paul Thomas  <pault@gcc.gnu.org>

    * gfortran.dg/move_alloc_17.f03: New test.
-------------- next part --------------
Index: gcc/fortran/check.c
===================================================================
*** gcc/fortran/check.c	(revision 241868)
--- gcc/fortran/check.c	(working copy)
*************** gfc_check_move_alloc (gfc_expr *from, gf
*** 3342,3347 ****
--- 3342,3357 ----
        return false;
      }
  
+   /*  F2003 12.4.1.7  */
+   if (to->expr_type == EXPR_VARIABLE && from->expr_type ==EXPR_VARIABLE
+       && !strcmp (to->symtree->n.sym->name, from->symtree->n.sym->name))
+     {
+       gfc_error ("The FROM and TO arguments at %L are either the same object "
+ 		 "or subobjects thereof and so violate aliasing restrictions "
+ 		 "(F2003 12.4.1.7)", &to->where);
+       return false;
+     }
+ 
    /* CLASS arguments: Make sure the vtab of from is present.  */
    if (to->ts.type == BT_CLASS && !UNLIMITED_POLY (from))
      gfc_find_vtab (&from->ts);
Index: gcc/testsuite/gfortran.dg/move_alloc_17.f90
===================================================================
*** gcc/testsuite/gfortran.dg/move_alloc_17.f90	(revision 0)
--- gcc/testsuite/gfortran.dg/move_alloc_17.f90	(working copy)
***************
*** 0 ****
--- 1,21 ----
+ ! { dg-do compile }
+ !
+ ! The call to MOVE_ALLOC below caused a seg fault in runtime.
+ ! This was discussed in:
+ ! https://groups.google.com/forum/#!topic/comp.lang.fortran/ZVLqXFYDZ0M
+ ! Richard Maine proposed that the code violated the restrictions on
+ ! actual arguments in F2003 12.4.1.7 and so the fix asserts that the
+ ! TO and FROM arguments cannot be the same object or subobjects thereof.
+ !
+ !
+ program test_move_alloc
+   type :: linked_list
+      type(linked_list), allocatable :: link
+      integer :: value
+   end type linked_list
+   type(linked_list) :: test
+ 
+   allocate(test % link)
+   allocate(test % link % link)
+   call move_alloc(test % link, test % link % link) ! { dg-error "aliasing restrictions" }
+ end program test_move_alloc