To: J3                                                          07-150r1
From: Bill Long and John Reid
Subject: Co-array allocation and collective calls
Date: 2007 February 14
Reference: J3/07-007, 07-103


Discussion

1. There is a problem re allocating and deallocating an allocatable
co-array that is a dummy argument. We require the same statement to be
involved, but the dummy argument might be associated with different
co-arrays on different images. We need to require that on each image
the dummy co-array be associated (perhaps through many levels of the
call chain) with the same non-dummy co-array. We introduce a new term,
"ultimate argument", to identify the non-dummy argument at the top of
the call chain.

2. A similar problem occurs for a call of a collective procedure.

3. Was it intended to restrict the collectives to having a whole
co-array for their first actual argument? For example, should this
call be allowed:

    call co_sum(co_array(1:5), result(1:5))

Note that the restriction is not effective, as may be seen from the
example

    call jacket(co_array(1:5), result(1:5))
     :
    subroutine jacket(co_array, result)
    real :: co_array(5)[*], result(5)
    call co_sum(co_array, result)
     :

To remove the restriction, we define a new term "co-array compatible"
and use it in the definitions of the collectives.


Edits to J3/07-007

[128:6]. In 6.3.1 ALLOCATE statement, at the end of the paragraph that
starts "If an <allocation> specifies a co-array", add "If the co-array
is a dummy argument, its ultimate argument shall be the same co-array
on every image."

[132:1]. In 6.3.3.1 Deallocation of allocatable variables, at the end
of the penultimate paragraph, add "If the co-array is a dummy
argument, its ultimate argument shall be the same co-array on every
image."

[314:18] At the end of 12.5.2.3 Argument association, add to the final
paragraph:

"The <<ultimate argument>> is the effective argument if the effective
argument is not a dummy argument or a subobject of a dummy argument.
If the effective argument is a dummy argument, the ultimate argument
is the ultimate argument of that dummy argument. If a given dummy
argument has an effective argument that is part of a second dummy
argument, the ultimate argument of the given dummy argument is the
corresponding part of the ultimate argument of the second dummy
argument."


[319:27] In 12.5.2.9 Co-array arguments, at the end of the second
paragraph, add: "Such an actual argument is called <<co-array
compatible>>".

[342:20-23]. Reword the text of 13.2.4 Arguments to collective
subroutines to:

"Each actual argument to a collective subroutine shall have the same
shape on all images of the team. Each actual argument associated with
an INTENT(IN) argument of type IMAGE_TEAM shall have a value that was
constructed by an invocation of FORM_TEAM for the team on that image.
The ultimate argument of each co-array dummy argument shall be the
same on every image of the team."

[363:13+],[363:23+],[364:8+]. For the MASK argument of 13.7.32 CO_ALL,
13.7.33 CO_ANY, and 13.7.34 CO_COUNT, replace "a co-array" by
"co-array compatible and".

[365:8+],[365:18+],[366:8+],[366:18+],[367:9+],[367:19+]. For the
CO_ARRAY argument of 13.7.36 CO_MAXLOC, 13.7.37 CO_MAXVAL, 13.7.38
CO_MINLOC, 13.7.39 CO_MINVAL, 13.7.40 CO_PRODUCT, and 13.7.41 CO_SUM,
replace "a co-array" by "co-array compatible and".

Note to editor: If paper 07-103 (adds the CO_FINDLOC intrinsic) is
adopted then the description of the CO_ARRAY argument to CO_FINDLOC
should be modified in the same was as for CO_MINLOC above.