On Fri, Nov 14, 2014 at 4:21 PM, Kenneth Graunke <kenn...@whitecape.org> wrote:
> On Thursday, November 13, 2014 04:28:20 PM Kristian Høgsberg wrote:
>> This patch uses the previous refactoring to add a new run_vs() method
>> that generates vertex shader code using the scalar visitor and
>> optimizer.
>>
>> Signed-off-by: Kristian Høgsberg <k...@bitplanet.net>
>> ---
>> src/mesa/drivers/dri/i965/brw_fs.cpp | 99 ++++++++-
>> src/mesa/drivers/dri/i965/brw_fs.h | 21 +-
>> src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 303
> ++++++++++++++++++++++++++-
>> 3 files changed, 412 insertions(+), 11 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> index 4dce0a2..8007977 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> @@ -1828,6 +1828,56 @@ fs_visitor::assign_urb_setup()
>> urb_start + prog_data->num_varying_inputs * 2;
>> }
>>
>> +void
>> +fs_visitor::assign_vs_urb_setup()
>> +{
>> + brw_vs_prog_data *vs_prog_data = (brw_vs_prog_data *) prog_data;
>> + int grf, count, slot, channel, attr;
>> +
>> + assert(stage == MESA_SHADER_VERTEX);
>> + count = _mesa_bitcount_64(vs_prog_data->inputs_read);
>> + if (vs_prog_data->uses_vertexid || vs_prog_data->uses_instanceid)
>> + count++;
>> +
>> + /* Each attribute is 4 regs. */
>> + this->first_non_payload_grf =
>> + payload.num_regs + prog_data->curb_read_length + count * 4;
>> +
>> + unsigned vue_entries =
>> + MAX2(count, vs_prog_data->base.vue_map.num_slots);
>> +
>> + vs_prog_data->base.urb_entry_size = ALIGN(vue_entries, 4) / 4;
>> + vs_prog_data->base.urb_read_length = (count + 1) / 2;
>> +
>> + assert(vs_prog_data->base.urb_read_length <= 15);
>
> What enforces this assertion? It obviously needs to be true, since
> the "Vertex URB Entry Read Length" field in 3DSTATE_VS has a maximum
> value of 15 in SIMD8 mode.
>
> But this looks like the exact same calculation done in
> vec4_vs_visitor::setup_attributes, and the limit there is [1, 63].
>
> The documentation indicates that the API may allow more vertex attributes
> than can practically be supported by pushing VUEs in as payload registers:
>
> "The EU limit of 128 GRFs imposes a maximum limit of 30 elements per vertex
> pushed into the payload, though the practical limit may be lower. If input
> vertices exceed the practical limit, software must decide between resorting
> to pulling elements during thread execution or dropping back to SIMD4x2
> dispatch."
>
> I don't see any code in this series for falling back, nor for pulling VUEs
> out of the URB (and avoiding overwriting them before they're loaded), so
> I expect this would simply assert fail on a vertex shader with too many
> inputs.
We only advertise the spec required minimum of 16 vertex attributes
right now. The 3DSTATE_VS field counts pairs of vertex attributes
which means we can handle up to 30 in scalar mode.
Kristian
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