Am 12.06.2018 um 01:17 schrieb Rob Clark:
> On Mon, Jun 11, 2018 at 6:59 PM, Roland Scheidegger <srol...@vmware.com>
> wrote:
>> Am 12.06.2018 um 00:32 schrieb Jason Ekstrand:
>>> On Wed, Jun 6, 2018 at 7:43 AM, Rob Clark <robdcl...@gmail.com
>>> <mailto:robdcl...@gmail.com>> wrote:
>>>
>>> Signed-off-by: Rob Clark <robdcl...@gmail.com
>>> <mailto:robdcl...@gmail.com>>
>>> ---
>>> I can't say for sure that this will work on all drivers, but it is
>>> what the blob driver does, and it seems to make deqp happy. I could
>>> move this to it's own pass inside ir3, but that seemed like overkill
>>>
>>> src/compiler/nir/nir.h | 10 ++++++++++
>>> src/compiler/nir/nir_lower_system_values.c | 17 +++++++++++++++++
>>> src/gallium/drivers/freedreno/ir3/ir3_nir.c | 1 +
>>> 3 files changed, 28 insertions(+)
>>>
>>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>>> index 073ab4e82ea..de3d55d83af 100644
>>> --- a/src/compiler/nir/nir.h
>>> +++ b/src/compiler/nir/nir.h
>>> @@ -1963,6 +1963,16 @@ typedef struct nir_shader_compiler_options {
>>> */
>>> bool lower_base_vertex;
>>>
>>> + /**
>>> + * If enabled, gl_HelperInvocation will be lowered as:
>>> + *
>>> + * !((1 << gl_SampleID) & gl_SampleMaskIN[0]))
>>>
>>>
>>> This only works for multi-sampling. What about the single-sampled case?
>> It doesn't make sense to me for msaa neither.
>> gl_SampleID forces per-sample execution, which clearly isn't what you
>> want.
>
> open to suggestions about how to try and force blob to do something
> different.. I tried a few things and the blob popped out shader code
> that worked the same way in all cases, but ofc I could have missed
> something.
>
>> Plus, gl_SampleMaskIN is specified to only contain bits for the
>> current shader invocation, so for msaa with forced per-sample execution
>> that would only contain the single bit corresponding to gl_SampleID
>> anyway (that is my interpretation at least - I know hw sample mask
>> inputs will probably always contains all the bits from rasterization,
>> regardless of gl_SampleID), so the "1 << gl_SampleID &" part will do
>> nothing at all. So I think that part is more about lowering the hw
>> rasterization sample mask to gl_SampleMaskIN rather than lowering to
>> gl_HelperInvocation.
>> But yes, !gl_SampleMaskIN should give gl_HelperInvocation - I think all
>> hw can give you raster sample mask even without msaa but I'm not
>> entirely sure if it's guaranteed to work in GL with single sampling
>> (similar for sample id, which should just be stuck at 0). But using the
>> gl names here looks very, very fishy to me here.
>
> I *guess* this is relying on behaviour that gl does not guarantee, but
> also doesn't prohibit, but the hw happens work that way and it works
> out..
>
> Maybe the answer is to simply better document the assumptions that
> this lowering depends on?
Well I think if you have a nir shader which uses sample id but is
supposed to not be run per-sample that is quite confusing (I'd just
assume that adrenos will use sample id 0 just like in single sampled
case). Hopefully noone will deduce shader frequency from the nir shader...
I'm definitely no NIR expert but there's quite a lot of hacky
assumptions in there:
- sample id in nir doesn't cause per-sample execution (and needs to be 0
in case of msaa but no per-sample execution)
- sampleMaskIn is available in single-sampled
- sampleMaskIn doesn't actually have gl semantics but hw ones (so simply
the mask from rasterization, not taking into account the sample id
already if there's per-sample execution (for legitimate reasons),
although as mentioned I think there's still some debate about this and
not all drivers may actually agree what the semantics of it are in case
of per-sample execution)
As such I'm not sure it really makes sense to do that as a generic
lowering pass? Albeit you're quite right that it might work for a lot of
hw... But some comments would at the very least imho definitely be required.
Roland
>
> BR,
> -R
>
>>
>> Roland
>>
>>
>>
>>
>>>
>>> --Jason
>>>
>>>
>>>
>>> + *
>>> + * TODO any hw w/ more than 32 samples? For them (if they
>>> + * used this option), a bit more math would be involved.
>>> + */
>>> + bool lower_helper_invocation;
>>> +
>>> bool lower_cs_local_index_from_id;
>>>
>>> bool lower_device_index_to_zero;
>>> diff --git a/src/compiler/nir/nir_lower_system_values.c
>>> b/src/compiler/nir/nir_lower_system_values.c
>>> index 487da042620..6668cbb5dcd 100644
>>> --- a/src/compiler/nir/nir_lower_system_values.c
>>> +++ b/src/compiler/nir/nir_lower_system_values.c
>>> @@ -136,6 +136,23 @@ convert_block(nir_block *block, nir_builder *b)
>>> nir_load_first_vertex(b));
>>> break;
>>>
>>> + case SYSTEM_VALUE_HELPER_INVOCATION:
>>> + if (b->shader->options->lower_helper_invocation) {
>>> + nir_ssa_def *tmp;
>>> +
>>> + tmp = nir_ushr(b,
>>> + nir_imm_int(b, 1),
>>> + nir_load_sample_id(b));
>>> +
>>> + tmp = nir_iand(b,
>>> + nir_load_sample_mask_in(b),
>>> + tmp);
>>> +
>>> + sysval = nir_inot(b, nir_i2b(b, tmp));
>>> + }
>>> +
>>> + break;
>>> +
>>> case SYSTEM_VALUE_INSTANCE_INDEX:
>>> sysval = nir_iadd(b,
>>> nir_load_instance_id(b),
>>> diff --git a/src/gallium/drivers/freedreno/ir3/ir3_nir.c
>>> b/src/gallium/drivers/freedreno/ir3/ir3_nir.c
>>> index cd1f9c526f2..341d990b269 100644
>>> --- a/src/gallium/drivers/freedreno/ir3/ir3_nir.c
>>> +++ b/src/gallium/drivers/freedreno/ir3/ir3_nir.c
>>> @@ -51,6 +51,7 @@ static const nir_shader_compiler_options options = {
>>> .lower_extract_byte = true,
>>> .lower_extract_word = true,
>>> .lower_all_io_to_temps = true,
>>> + .lower_helper_invocation = true,
>>> };
>>>
>>> struct nir_shader *
>>> --
>>> 2.17.0
>>>
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