[Mesa-dev] [RFC v1] i965/vec4: add a swizzle check on the uniform bail condition

[Matt Turner]

On Wed, Sep 23, 2015 at 1:07 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Sep 23, 2015 12:29, "Alejandro Piñeiro" <apinheiro at igalia.com> wrote:
>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>> b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>> index d3f0ddd..400a13a 100644
>> --- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
>> @@ -325,7 +325,8 @@ try_copy_propagate(const struct brw_device_info
>> *devinfo,
>>         inst->opcode == SHADER_OPCODE_GEN4_SCRATCH_WRITE)
>>        return false;
>>
>> -   if (inst->is_3src() && value.file == UNIFORM)
>> +   if (inst->is_3src() && value.file == UNIFORM &&
>> +
>> !brw_is_single_value_swizzle(brw_compose_swizzle(inst->src[arg].swizzle,
>> value.swizzle)))
>
> This is a case where we probably want to do the check after we've created
> the "final" value.  The question that's being asked is "is this final value
> allowed?"

I think that's what the brw_compose_swizzle() is doing -- combining
the swizzles and then asking if the result is single-valued.

> Also, we emitted it before with the is_visitor code. What checks are we
> doing there to make sure we only emitted the uniform directly if it was OK
> to do so?

Look at vec4_visitor::fix_3src_operand():

   if (src.file == UNIFORM && brw_is_single_value_swizzle(src.swizzle))
      return src;

so it was doing the right thing.