[Mesa-dev] [PATCH] nir: fix compacting varyings when XFB outputs are present

[Timothy Arceri]

On 10/10/18 7:25 pm, Samuel Pitoiset wrote:
> On 10/10/18 10:14 AM, Timothy Arceri wrote:
>> On 10/10/18 6:44 pm, Samuel Pitoiset wrote:
>>> We shouldn't try to compact any varyings known as always
>>> active IO, especially XFB outputs. For example, if one
>>> component of an xfb output is also used as input varying
>>> in the next stage, it shouldn't be compacted.
>>>
>>> Because we look at the input varyings from the consumer
>>> stage, we don't know if one of them is an XFB output. One
>>> solution is to mark all components as used when
>>> always_active_io is true to avoid wrong remapping.
>>>
>>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>>> ---
>>>   src/compiler/nir/nir_linking_helpers.c | 9 +++++++++
>>>   1 file changed, 9 insertions(+)
>>>
>>> diff --git a/src/compiler/nir/nir_linking_helpers.c 
>>> b/src/compiler/nir/nir_linking_helpers.c
>>> index 85712a7cb1..88014e9a1d 100644
>>> --- a/src/compiler/nir/nir_linking_helpers.c
>>> +++ b/src/compiler/nir/nir_linking_helpers.c
>>> @@ -236,6 +236,15 @@ get_slot_component_masks_and_interp_types(struct 
>>> exec_list *var_list,
>>>                  get_interp_type(var, default_to_smooth_interp);
>>>               interp_loc[location + i] = get_interp_loc(var);
>>> +            if (var->data.always_active_io) {
>>> +               /* Mark all components as used to avoid repacting xfb 
>>> varyings
>>> +                * wrongly. For instance, if one component of an xfb 
>>> output is
>>> +                * also used as input varying in the next stage.
>>> +                */
>>> +               comps[location + i] |= 0xf;
>>> +               continue;
>>> +            }
>>
>> In GLSL we specifically mark the corresponding inputs as 
>> always_active_io. I think we should try to do that for spirv also 
>> otherwise we are going to run into issues with the other lowering 
>> passes that check always_active_io such as scalar/array lowering.
> 
> https://cgit.freedesktop.org/mesa/mesa/commit/?id=a1bc1523408a305b14a8c297ea93a28bb12cee5d 
> 
> 
> Should be enough?

I haven't read the spec but if its the same as GLSL that probably only 
sets it on outputs.

> 
>>
>>> +
>>>               if (dual_slot) {
>>>                  if (i & 1) {
>>>                     comps[location + i] |= ((1 << comps_slot2) - 1);
>>>