[J3] [BULK] Re: [EXTERNAL] Should all intrinsic functions be simple?

[Clune, Thomas L. (GSFC-6101)]

Reuben,

I think it is the other way around.   The definition of SIMPLE is missing a bit that might be hard to define in the standard.   If so then we need a more nuanced list of SIMPLE intrinsics.

The key thing with the “bad” intrinsic procedures is that there is an implicit context that is accessed when they run.   I strongly suspect that under-the-hood, there is the equivalent of COMMON/Save in the form of some private state inside the run-time library.

This is one of the reasons I was uncomfortable with the coarray approach of not passing an object to the intrinsics.   With MPI we have a “comm” object that  controls access.    (MPI has other sins, so just defending the value of biting the bullet and accepting another argument can be a good thing in an intrinsic.)


  *   Tom

From: J3 <j3-bounces at mailman.j3-fortran.org> on behalf of j3 <j3 at mailman.j3-fortran.org>
Reply-To: j3 <j3 at mailman.j3-fortran.org>
Date: Tuesday, December 19, 2023 at 2:59 PM
To: j3 <j3 at mailman.j3-fortran.org>
Cc: "Reuben D. Budiardja" <reubendb at ornl.gov>
Subject: [BULK] Re: [J3] [EXTERNAL] Should all intrinsic functions be simple?

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On 12/19/23 11:04, Brad Richardson via J3 wrote:

<snipped>

However, that would not
necessarily be true for all of the intrinsic functions. Take the
following example:

cur_team = get_team()
...
change team (new_team)
    cur_team = get_team()
    ...
end team

Clearly, it is intended that the two calls to get_team return different
results, so common subexpression elimination would not be valid here.
Also, conceptually, it would not be possible to implement this call in
a way that does "not contain a designator of a variable that is
accessed by use or host association" or "not contain a reference to a
variable in a common block" as it clearly must be accessing some global
state of the program.

Intrinsic functions which may be affected include:

* failed_images
* get_team
* image_index
* num_images
* stopped_images
* team_number
* this_image

I think this is conflating what a compiler may need to do with the
actual program. From the program standpoint, the example above does not
violate any of the simple-ness constraints (or any of the listed
function). So I still think they are SIMPLE.

Best,
Reuben

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