[Mesa-dev] [PATCH 7/9] i965/fs: Handle VS inputs in the NIR backend.

[Jason Ekstrand]

I think I mentioned this at least once before, but I don't think that this
is a good long-term solution.  The nir_lower_io function does two things
primarily.  1) It assigns each variable a "device location" and 2) changes
the variable loads to loads with an offset.  In the long-term, I think we
want to split 1) out and let the backend control what "device location"
gets assigned to each input/output.  Then, add a knob to 2) to select how
we want things packed.  Doing this will let us avoid this whole re-mapping
mess and, in the case of uniforms, better control things so that we can
push some of them.  That said, this is *not* a NAK of the current patch.
If you want to hold off on that for a while, this looks ok.
--Jason

On Mon, Mar 9, 2015 at 1:58 AM, Kenneth Graunke <kenneth at whitecape.org>
wrote:

> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> index 3baafc4..1734d03 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> @@ -199,11 +199,32 @@ fs_visitor::nir_setup_inputs(nir_shader *shader)
>     struct hash_entry *entry;
>     hash_table_foreach(shader->inputs, entry) {
>        nir_variable *var = (nir_variable *) entry->data;
> +      enum brw_reg_type type = brw_type_for_base_type(var->type);
>        fs_reg input = offset(nir_inputs, var->data.driver_location);
>
>        fs_reg reg;
>        switch (stage) {
> -      case MESA_SHADER_VERTEX:
> +      case MESA_SHADER_VERTEX: {
> +         /* Our ATTR file is indexed by VERT_ATTRIB_*, which is the value
> +          * stored in nir_variable::location.
> +          *
> +          * However, NIR's load_input intrinsics use a different index -
> an
> +          * offset into a single contiguous array containing all inputs.
> +          * This index corresponds to the nir_variable::driver_location
> field.
> +          *
> +          * So, we need to copy from fs_reg(ATTR, var->location) to
> +          * offset(nir_inputs, var->data.driver_location).
> +          */
> +         unsigned components = var->type->without_array()->components();
> +         unsigned array_length = var->type->is_array() ?
> var->type->length : 1;
> +         for (unsigned i = 0; i < array_length; i++) {
> +            for (unsigned j = 0; j < components; j++) {
> +               emit(MOV(retype(offset(input, components * i + j), type),
> +                        offset(fs_reg(ATTR, var->data.location + i,
> type), j)));
> +            }
> +         }
> +         break;
> +      }
>        case MESA_SHADER_GEOMETRY:
>        case MESA_SHADER_COMPUTE:
>           unreachable("fs_visitor not used for these stages yet.");
> --
> 2.2.1
>
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