[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> 2010-10-02 11:33:43 UTC ---
Summary as far I understand it. Cf.
http://j3-fortran.org/pipermail/j3/2010-September/003852.html :

module m
  procedure(), pointer :: p, p2
  protected :: p
end module m

subroutine two
  use m
  procedure(), pointer :: ptr2
  ptr2 => p  ! Invalid
end subroutine two

It is invalid as "p" is PROTECTED, but gfortran does not diagnose this. That's
something the variable-definition patch misses.

 * * *

subroutine one
  use m
  procedure(), pointer :: ptr1 => p2
end subroutine one

That's invalid as "p2" is a pointer, cf. PR 45290.

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

janus at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.10.02 13:25:23
     Ever Confirmed|0                           |1

--- Comment #4 from janus at gcc dot gnu.org 2010-10-02 13:25:23 UTC ---
Note: The problem not only applies to procedure pointers, but also to data
pointers, as the following example shows:


module m
  integer, pointer :: p
  protected :: p
end module m

  use m
  integer, pointer :: ptr2
  ptr2 => p  ! Invalid per F08:C551 (undiagnosed)
end

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

--- Comment #5 from janus at gcc dot gnu.org 2010-10-02 14:19:18 UTC ---
(In reply to comment #4)
> Note: The problem not only applies to procedure pointers, but also to data
> pointers, as the following example shows:

Well, at least this example is invalid by the same logic as the original test
case. However, I'm not sure I fully understand this logic ...

In contrast to my annotation in the previous example, C551 does not apply
(since it only talks about nonpointers). And C552 only says that a protected
pointer cannot appear in a "pointer association context" (i.e. the LHS of a
pointer assignment). It does not say that a protected pointer cannot appear on
the RHS of a pointer assignment!?!

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID

--- Comment #6 from Tobias Burnus <burnus at gcc dot gnu.org> 2010-10-02 14:39:30 UTC ---
(In reply to comment #5)
> In contrast to my annotation in the previous example, C551 does not apply
> (since it only talks about nonpointers). And C552 only says that a protected
> pointer cannot appear in a "pointer association context" (i.e. the LHS of a
> pointer assignment). It does not say that a protected pointer cannot appear on
> the RHS of a pointer assignment!?!

I think I scratch that part. I still do not see what is meant by the
"proc-pointer" part in

"C551 A nonpointer object that has the PROTECTED attribute and is accessed by
use association shall not appear [...] as the [...] proc-target in a
pointer-assignment-stmt."

as PROTECTED can only be applied to proc pointers (and normal variables).


I think I will close this PR as INVALID - as the other issue is taken care of
in 
PR 45290.

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

janus at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |

--- Comment #7 from janus at gcc dot gnu.org 2010-10-02 15:25:04 UTC ---
(In reply to comment #6)
> I still do not see what is meant by the
> "proc-pointer" part in
> 
> "C551 A nonpointer object that has the PROTECTED attribute and is accessed by
> use association shall not appear [...] as the [...] proc-target in a
> pointer-assignment-stmt."
> 
> as PROTECTED can only be applied to proc pointers (and normal variables).

Ok, I think the only way this half-sentence and the interpretation on the J3
mailing list make sense, is via the following interpretation. Consider:

integer, pointer :: lhs, rhs
lhs => rhs

In such a pointer assignment statement, the object on the right hand side
supposedly does not have the pointer attribute (the pointer is dereferenced, so
that 'lhs' will point to the target of 'rhs'). With this reading, C551 can be
applied to (proc-/data-)pointer assignments as well, and the sentence about
'proc-target' does make sense.

[I hate these kinds of subtleties in reading the standard and hope I got it
right this time.]

Also, from a "common sense" POV, it is important to reject protected pointers
on the rhs of a pointer assignment, otherwise the PROTECTED feature could be
circumvented this way.

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

janus at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
         AssignedTo|unassigned at gcc dot       |janus at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #8 from janus at gcc dot gnu.org 2010-10-02 18:51:21 UTC ---
Patch:


Index: gcc/fortran/expr.c
===================================================================
--- gcc/fortran/expr.c    (revision 164900)
+++ gcc/fortran/expr.c    (working copy)
@@ -3250,6 +3250,14 @@ gfc_check_pointer_assign (gfc_expr *lvalue, gfc_ex
       return FAILURE;
     }

+  /* Check for F08:C551.  */
+  if (rvalue->expr_type == EXPR_VARIABLE
+      && rvalue->symtree->n.sym->attr.is_protected
+      && rvalue->symtree->n.sym->attr.use_assoc)
+    gfc_error ("Variable '%s' is PROTECTED and can not appear in a "
+           "pointer assignment statement at %L",
+           rvalue->symtree->n.sym->name, &rvalue->where);
+
   proc_pointer = lvalue->symtree->n.sym->attr.proc_pointer;

   rank_remap = false;

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

--- Comment #9 from Tobias Burnus <burnus at gcc dot gnu.org> 2010-10-02 19:52:17 UTC ---
(In reply to comment #7)
> Ok, I think the only way this half-sentence and the interpretation on the J3
> mailing list make sense, is via the following interpretation.

I disagree and start to come to the conclusion that one should asked at the J3
mailing list - I just have no idea how to ask sensible for the proc-target part
of C551.

> Consider:
> integer, pointer :: lhs, rhs
> lhs => rhs
> 
> In such a pointer assignment statement, the object on the right hand side
> supposedly does not have the pointer attribute

Why? I see on the right hand side a "data-target" looks perfectly like a
pointer and matches also the definition
"Entities with the POINTER attribute can be associated with different data
objects or procedures during execution of a program."

I could do:
  rhs => targer
while (even if rhs were an array) I could not do
  rhs(4) => target

> that 'lhs' will point to the target of 'rhs'). With this reading, C551 can be
> applied to (proc-/data-)pointer assignments as well, and the sentence about
> 'proc-target' does make sense.

Well, it makes sense here - but you open at the same time the box of the
Pandora.

> Also, from a "common sense" POV, it is important to reject protected pointers
> on the rhs of a pointer assignment, otherwise the PROTECTED feature could be
> circumvented this way.

Actually: How? I see how you can modify the pointer target - but not the
pointer itself.


Thus:
- I think C551's "or proc-target" does not make sense as it is unreachable
- With regards to C551/C552 gfortan handles it seemingly correctly
- I need a stronger coffee when reading the fine prints of the Fortran standard

With your definition, you allow for:
  pointer :: ptr2 => ptr1
which is difficult to get correct and I believe is invalid as "ptr1" has the
POINTER and not the TARGET attribute. A POINTER is allowed for a normal,
non-initialization expression.

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

janus at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |INVALID

--- Comment #10 from janus at gcc dot gnu.org 2010-10-03 20:25:36 UTC ---
(In reply to comment #9)
> Thus:
> - I think C551's "or proc-target" does not make sense as it is unreachable
> - With regards to C551/C552 gfortan handles it seemingly correctly
> - I need a stronger coffee when reading the fine prints of the Fortran standard

Ok, I agree. I think I had misread Van Snyder's interpretation on the J3
mailing list (and possibly parts of the standard). Sorry about the confusion.
Closing as invalid.

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[burnus at gcc dot gnu dot org]

------- Comment #2 from burnus at gcc dot gnu dot org  2010-09-21 14:19 -------
(In reply to comment #1)
> TODO: Check whether the code is really invalid

I have now asked at J3,
cf. http://j3-fortran.org/pipermail/j3/2010-September/thread.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740

[Bug fortran/45740] PROCEDURE POINTER and PROTECTED: Accepts/ICEs on invalid code

[burnus at gcc dot gnu dot org]

------- Comment #1 from burnus at gcc dot gnu dot org  2010-09-21 13:47 -------
TODO: Check whether the code is really invalid - C551 talks only about
nonpointers, but it also talks about "proc-target" - which only applies to
procedures and the PROTECTED only applies per C549 to variables and procedure
pointers.


Re-reading F2008's "4.5.4.6 Default initialization for components" and R505 and
following, the
    procedure(), pointer :: ptr3 => p2  ! Valid
is invalid as "p2" does not have the target attribute.


-- 

burnus at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|ice-on-valid-code           |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45740