[Bug libgomp/97332] New: [gcn] GCN_NUM_GANGS/GCN_NUM_WORKERS override compile-time constants

[Bug libgomp/97332] New: [gcn] GCN_NUM_GANGS/GCN_NUM_WORKERS override compile-time constants

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97332

            Bug ID: 97332
           Summary: [gcn] GCN_NUM_GANGS/GCN_NUM_WORKERS override
                    compile-time constants
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

In openacc programs, dimensions are either dynamic or hardcoded.

If the dimensions are hardcoded, and there are builtins returning the size of
these dimensions, the builtins are folded in fold_internal_goacc_dim.

Changing the dimensions in the plugin then invalidates the folding.

I'm guessing this should be fixed, or at least documented in the plugin (with
perhaps even a warning).

[Bug libgomp/97332] [gcn] GCN_NUM_GANGS/GCN_NUM_WORKERS override compile-time constants

[ams at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97332

Andrew Stubbs <ams at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-10-08
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Stubbs <ams at gcc dot gnu.org> ---
At the point the overrides are applied (run_kernel) the code only knows what
dimensions were selected at runtime, not how those figures were arrived at. It
then prints (with GCN_DEBUG set) the "launch attributes" and "launch actuals".

To fix this the overrides will have to applied much earlier, and independently
for OpenACC (gcn_exec) and OpenMP (parse_target_attributes). That or the
automatic balancing be applied later. Or perhaps the original attributes be
stored for later inspection (but GOMP_kernel_launch_attributes is defined by
libgomp). The "attributes" and "actuals" will need to be overhauled. Probably
get_group_size can be removed.

It ought to be doable though.