RFA: Revamp fortran array types

[Toon Moene]

Tobias Burnus wrote:

> On 08/19/2009 03:01 PM, Michael Matz wrote:

>> On Wed, 19 Aug 2009, Toon Moene wrote:

>>> Two names must not refer to the same or overlapping storage unless you, 
>>> the programmer, indicate that they do (by either using EQUIVALENCE or 
>>> designating the storage with the TARGET attribute).

> I agree about TARGET, but I do not fully agree about EQUIVALENCE.
> Equivalenced variables share the same memory location, but only under
> certain restrictions on may make use of it. (Though the expectations of
> the users is probably more than what the standard guarantees.)

Ah, sorry.  The alias rules I tried to condense into a single sentence 
are about what you, the programmer can/not do *in case of writes*.

The following code is perfectly OK:

       DIMENSION A(10)
       A = 10.0
       CALL SUB(A,A)
       END
       SUBROUTINE SUB(A,B)
       REAL, INTENT(IN) :: A(:), B(:)
       ...
       END

Likewise, the following is OK, although its *meaning* is not specified 
by the Standard (i.e., the value of X is undefined):

       EQUIVALENCE(I,X)
       X = 10.0
       I = 10
       PRINT*,X
       END

There's no doubt, however, that setting I destroys the previous value of 
X (and that's the only interesting property of this code from the point 
of alias analysis, which, e.g., can't change the order of the assignment 
to X and I).

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
At home: http://moene.org/~toon/
Progress of GNU Fortran: http://gcc.gnu.org/gcc-4.5/changes.html