Hi!

On 2022-04-25T23:19:26+0200, I wrote:
> On 2022-04-20T19:06:17+0200, Jakub Jelinek <jakub@redhat.com> wrote:
>> So that move_sese_region_to_fn works properly, OpenMP/OpenACC constructs
>> for which that function is invoked need an extra artificial BIND_EXPR
>> around their body so that we move all variables of the bodies.
>>
>> The C/C++ FEs do that both for OpenMP constructs like OMP_PARALLEL, OMP_TASK
>> or OMP_TARGET and for OpenACC constructs that behave similarly to
>> OMP_TARGET, but the Fortran FE only does that for OpenMP constructs.
>>
>> The following patch does that for OpenACC constructs too.
>> This fixes ICE on the attached testcase.
>
> ACK, thanks.

>> Unfortunately, it also regresses
>> FAIL: gfortran.dg/goacc/privatization-1-compute-loop.f90   -O  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -O0  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -O1  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -O2  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -O3 -g  (test for excess errors)
>> FAIL: libgomp.oacc-fortran/privatized-ref-2.f90 -DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 -foffload=disable  -Os  (test for excess errors)
>> Those emits emit tons of various messages and now there are some extra ones,
>
> I've fixed these up.

One more issue became apparent, where the code changes pushed actually do
lead to a GCN offloading compilation failure:

    [...]/libgomp.oacc-fortran/print-1.f90: In function ‘MAIN__._omp_fn.0’:
    [...]/libgomp.oacc-fortran/print-1.f90:13:14: error: 512 bytes of gang-private data-share memory exhausted (increase with ‘-mgang-private-size=560’, for example)
       13 | !$acc parallel
          |              ^

In my configuration, I may indeed fix GCN offloading compilation with
'-foffload-options=amdgcn-amdhsa=-mgang-private-size=560', but I don't
think that's generally correct/sufficient, so in the the attached
"Fix up 'libgomp.oacc-fortran/print-1.f90' GCN offloading compilation
[PR104717]", I instead "raise '-mgang-private-size' to an arbitrary high
value".  This avoids having to route the actual 'sizeof' from GCC build
down to the test suite harness (which ought to be doable, but
non-trivial).  OK to push that:

    +! For GCN offloading compilation, when gang-privatizing 'dt_parm.N'
    +! (see below), we run into an 'gang-private data-share memory exhausted'
    +! error: the default '-mgang-private-size' is too small.  Per
    +! 'gcc/fortran/trans-io.cc'/'libgfortran/io/io.h', that one is
    +! 'struct st_parameter_dt', which indeed is rather big.  Instead of
    +! working out its exact size (which may vary per GCC configuration),
    +! raise '-mgang-private-size' to an arbitrary high value.
    +! { dg-additional-options "-foffload-options=amdgcn-amdhsa=-mgang-private-size=13579" { target openacc_radeon_accel_selected } }

... to master branch? (This doubles the use/testing of the
'-mgang-private-size' option!)  ;-)

We've currently not been doing OpenACC privatization scanning in
'libgomp.oacc-fortran/print-1.f90', which I've now added, to help
document the issue; no need to review that.

Of course, the issue could alternatively be fixed by adding more logic to
the GCN back end to auto-scale the allocation, or be fixed by adding more
logic to the compiler to avoid gang-privatizing varibales such as
'dt_parm.N' in such cases, but that's not something I'm going to look
into at this point.

Or, of course, be avoided by re-writing the test case to not require
gang-privatizing 'dt_parm.N', but the test case is correct as it is.


Grüße
 Thomas


>       PR fortran/104717
>       gcc/fortran/
>       * trans-openmp.cc (gfc_trans_oacc_construct): Wrap construct body
>       in an extra BIND_EXPR.

> --- a/gcc/fortran/trans-openmp.cc
> +++ b/gcc/fortran/trans-openmp.cc
> @@ -4444,7 +4444,9 @@ gfc_trans_oacc_construct (gfc_code *code)
>    gfc_start_block (&block);
>    oacc_clauses = gfc_trans_omp_clauses (&block, code->ext.omp_clauses,
>                                       code->loc, false, true);
> +  pushlevel ();
>    stmt = gfc_trans_omp_code (code->block->next, true);
> +  stmt = build3_v (BIND_EXPR, NULL, stmt, poplevel (1, 0));
>    stmt = build2_loc (gfc_get_location (&code->loc), construct_code,
>                    void_type_node, stmt, oacc_clauses);
>    gfc_add_expr_to_block (&block, stmt);


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