Layout specifier '[*]' interpretation in typedef

Originally reported on Google Code with ID 2
Constraint 6.5.1.1-14 states the following:

    14 If the layout qualifier is of the form ‘[ * ]’,
    the shared object is distributed as if it had a block size of
    ( sizeof(a) / upc_elemsizeof(a) + THREADS - 1 ) / THREADS,
    where ‘a’ is the array being distributed.

As described in Berkeley bug report 856
(https://upc-bugs.lbl.gov/bugzilla/show_bug.cgi?id=856#c3)
the specification does not explicitly state the required
interpretation for the following chain of typedef's.

    typedef int I;
    typedef I J[10];
    typedef shared [*] J K[10];
    typedef K L[10];
    K k;
    L l;

If '[*]' is bound to a specific block size when the typedef 'K'
is declared, then it will have the value: ceiling (100 / THREADS).
In this interpretation the block sizes of both the types K
and L are necessarily equal.  Therefore, the arrays 'k' and 'l'
have the same block size.

However, if '[*]' is allowed to propagate to the declaration of
L before it is evaluated, then the resulting block size of L
is: ceiling (1000 / THREADS).

The proposed interpretation is the first one: where '[*]'
is evaluated at the point of its use in a declaration
or type definition.

Note: this is the consensus interpretation of the Cray, SGI, MuPC,
and GCC/UPC compilers.

We propose that an additional constraint is added to
the specification which states the following:

    If the layout qualifier of the form '[*]' is present in a
    type definition, its value is calculated according to
    Constraint 14.  It is this value that will be used when the
    type definition is referenced in subsequent declarations.

The following example will be added in the same section.

    EXAMPLE:

    Both the types K and L below have the same block size,
    which is equal to: ceiling (100 / THREADS).

        typedef int I;
        typedef I J[10];
        typedef shared [*] J K[10];
        typedef K L[10];
Reported by gary.funck on 2012-03-09 18:34:56
Comments (8)
