[Mesa-dev] [PATCH v2] nir: Handle variables dependent on the local work group size.

[Karol Herbst]

On Sun, Nov 11, 2018 at 10:48 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
>
> On Sun, Nov 11, 2018 at 3:35 PM Plamena Manolova <plamena.n.manolova at gmail.com> wrote:
>>
>> Lowering shader variables which depend on the local work group
>> size being available in nir_lower_system_values is only possible
>> if the local work group size isn't variable, otherwise this should
>> be handled by the native driver (if it supports
>> ARB_compute_variable_group_size).
>>
>> Signed-off-by: Plamena Manolova <plamena.n.manolova at gmail.com>
>> ---
>>  src/compiler/nir/nir_lower_system_values.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/src/compiler/nir/nir_lower_system_values.c b/src/compiler/nir/nir_lower_system_values.c
>> index bde7eb1180..6fdf9f9c51 100644
>> --- a/src/compiler/nir/nir_lower_system_values.c
>> +++ b/src/compiler/nir/nir_lower_system_values.c
>> @@ -77,6 +77,15 @@ convert_block(nir_block *block, nir_builder *b)
>>            *    "The value of gl_GlobalInvocationID is equal to
>>            *    gl_WorkGroupID * gl_WorkGroupSize + gl_LocalInvocationID"
>>            */
>> +
>> +         /*
>> +          * If the local work group size is variable we can't lower the global
>> +          * invocation id here.
>
>
> Why not?
>
>>
>> +          */
>> +         if (b->shader->info.cs.local_size_variable) {
>
>
> I didn't realize we'd added a bit for this.  At one point in time, Karol had patches which had it keyed off of the size being zero.  Having a separate bit is probably fine, it just surpised me.
>


yeah.. I guess I choose that, because I had nothing better. But I
guess having the size being 0 is good enough as long as we sure it is
0 in relevant cases.

>>
>> +            break;
>> +         }
>> +
>>           nir_ssa_def *group_size = build_local_group_size(b);
>>           nir_ssa_def *group_id = nir_load_work_group_id(b);
>>           nir_ssa_def *local_id = nir_load_local_invocation_id(b);
>> @@ -115,6 +124,11 @@ convert_block(nir_block *block, nir_builder *b)
>>        }
>>
>>        case SYSTEM_VALUE_LOCAL_GROUP_SIZE: {
>> +         /* If the local work group size is variable we can't lower it here */
>> +         if (b->shader->info.cs.local_size_variable) {
>> +            break;
>> +         }
>> +
>>           sysval = build_local_group_size(b);
>>           break;
>>        }
>> @@ -189,6 +203,14 @@ convert_block(nir_block *block, nir_builder *b)
>>           break;
>>
>>        case SYSTEM_VALUE_GLOBAL_GROUP_SIZE: {
>> +         /*
>> +          * If the local work group size is variable we can't lower the global
>> +          * group size here.
>> +          */
>> +         if (b->shader->info.cs.local_size_variable) {
>> +            break;
>> +         }
>
>
> Why can't we lower the global size?  It seems like we would want the below multiplication regardless of whether the local size is constant.
>

well I am not sure about ARB_compute_variable_group_size, but at least
in CL you know nothing about it at compile time as you specify
everything when you enqueue the kernel. Could be that the number of
work_groups is fixed with ARB_compute_variable_group_size though?

>>
>> +
>>           nir_ssa_def *group_size = build_local_group_size(b);
>>           nir_ssa_def *num_work_groups = nir_load_num_work_groups(b);
>>           sysval = nir_imul(b, group_size, num_work_groups);
>> --
>> 2.11.0
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev