[Mesa-dev] [PATCH] glsl: Handle attribute aliasing in attribute storage limit check.

[Ilia Mirkin]

On Wed, Sep 2, 2015 at 2:20 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> In various versions of OpenGL and GLSL, it's possible to declare
> multiple VS input variables with aliasing attribute locations.
>
> So, when computing the storage requirements for vertex attributes,
> we can't simply add up the sizes.  Instead, we need to look at the
> enabled slots.
>
> This patch begins tracking which attributes are double types that
> are larger than 128-bits (i.e. take up two vec4 slots).  We then
> count normal attributes once, and count the double-size attributes
> a second time.
>
> Fixes deQP functional.attribute_location.bind_aliasing.max_cond_* tests
> on i965, which regressed with commit ad208d975a6d3aebe14f7c2c16039ee20.

This is all subtle stuff. I'd feel a whole lot better if there were
some piglit coverage for this.

>
> Cc: "10.6 11.0" <mesa-stable at lists.freedesktop.org>
> Cc: Matt Turner <mattst88 at gmail.com.
> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
> Cc: Dave Airlie <airlied at gmail.com>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/glsl/linker.cpp | 64 ++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 36 insertions(+), 28 deletions(-)
>
> diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
> index 47f7d25..934062f 100644
> --- a/src/glsl/linker.cpp
> +++ b/src/glsl/linker.cpp
> @@ -2339,6 +2339,7 @@ assign_attribute_or_color_locations(gl_shader_program *prog,
>      */
>     unsigned used_locations = (max_index >= 32)
>        ? ~0 : ~((1 << max_index) - 1);
> +   unsigned double_storage_locations = 0;
>
>     assert((target_index == MESA_SHADER_VERTEX)
>           || (target_index == MESA_SHADER_FRAGMENT));
> @@ -2452,34 +2453,6 @@ assign_attribute_or_color_locations(gl_shader_program *prog,
>
>        const unsigned slots = var->type->count_attribute_slots();
>
> -      /* From GL4.5 core spec, section 11.1.1 (Vertex Attributes):
> -       *
> -       * "A program with more than the value of MAX_VERTEX_ATTRIBS active
> -       * attribute variables may fail to link, unless device-dependent
> -       * optimizations are able to make the program fit within available
> -       * hardware resources. For the purposes of this test, attribute variables
> -       * of the type dvec3, dvec4, dmat2x3, dmat2x4, dmat3, dmat3x4, dmat4x3,
> -       * and dmat4 may count as consuming twice as many attributes as equivalent
> -       * single-precision types. While these types use the same number of
> -       * generic attributes as their single-precision equivalents,
> -       * implementations are permitted to consume two single-precision vectors
> -       * of internal storage for each three- or four-component double-precision
> -       * vector."
> -       * Until someone has a good reason in Mesa, enforce that now.
> -       */
> -      if (target_index == MESA_SHADER_VERTEX) {
> -        total_attribs_size += slots;
> -        if (var->type->without_array() == glsl_type::dvec3_type ||
> -            var->type->without_array() == glsl_type::dvec4_type ||
> -            var->type->without_array() == glsl_type::dmat2x3_type ||
> -            var->type->without_array() == glsl_type::dmat2x4_type ||
> -            var->type->without_array() == glsl_type::dmat3_type ||
> -            var->type->without_array() == glsl_type::dmat3x4_type ||
> -            var->type->without_array() == glsl_type::dmat4x3_type ||
> -            var->type->without_array() == glsl_type::dmat4_type)
> -           total_attribs_size += slots;
> -      }
> -
>        /* If the variable is not a built-in and has a location statically
>         * assigned in the shader (presumably via a layout qualifier), make sure
>         * that it doesn't collide with other assigned locations.  Otherwise,
> @@ -2594,6 +2567,38 @@ assign_attribute_or_color_locations(gl_shader_program *prog,
>             }
>
>             used_locations |= (use_mask << attr);
> +
> +            /* From the GL 4.5 core spec, section 11.1.1 (Vertex Attributes):
> +             *
> +             * "A program with more than the value of MAX_VERTEX_ATTRIBS
> +             *  active attribute variables may fail to link, unless
> +             *  device-dependent optimizations are able to make the program
> +             *  fit within available hardware resources. For the purposes
> +             *  of this test, attribute variables of the type dvec3, dvec4,
> +             *  dmat2x3, dmat2x4, dmat3, dmat3x4, dmat4x3, and dmat4 may
> +             *  count as consuming twice as many attributes as equivalent
> +             *  single-precision types. While these types use the same number
> +             *  of generic attributes as their single-precision equivalents,
> +             *  implementations are permitted to consume two single-precision
> +             *  vectors of internal storage for each three- or four-component
> +             *  double-precision vector."
> +             *
> +             * Mark this attribute slot as taking up twice as much space
> +             * so we can count it properly against limits.  According to
> +             * issue (3) of the GL_ARB_vertex_attrib_64bit behavior, this
> +             * is optional behavior, but it seems preferable.
> +             */
> +            const glsl_type *type = var->type->without_array();
> +            if (type == glsl_type::dvec3_type ||
> +                type == glsl_type::dvec4_type ||
> +                type == glsl_type::dmat2x3_type ||
> +                type == glsl_type::dmat2x4_type ||
> +                type == glsl_type::dmat3_type ||
> +                type == glsl_type::dmat3x4_type ||
> +                type == glsl_type::dmat4x3_type ||
> +                type == glsl_type::dmat4_type) {
> +               double_storage_locations |= (use_mask << attr);
> +            }
>          }
>
>          continue;
> @@ -2605,6 +2610,9 @@ assign_attribute_or_color_locations(gl_shader_program *prog,
>     }
>
>     if (target_index == MESA_SHADER_VERTEX) {
> +      unsigned total_attribs_size =
> +         _mesa_bitcount(used_locations & ((1 << max_index) - 1)) +
> +         _mesa_bitcount(double_storage_locations);

Does this also need the & ((1 << max_index) - 1) treatment? [Well, not
_need_ but seems like it'd avoid needlessly counting things?]

>        if (total_attribs_size > max_index) {
>          linker_error(prog,
>                       "attempt to use %d vertex attribute slots only %d available ",
> --
> 2.5.0
>