[Mesa-dev] [PATCH 2/2] glsl/linker: location aliasing requires types to have the same width

[Ilia Mirkin]

On Fri, Nov 3, 2017 at 6:56 AM, Iago Toral Quiroga <itoral at igalia.com> wrote:
> Regarding location aliasing requirements, the OpenGL spec says:
>
>   "Further, when location aliasing, the aliases sharing the location
>    must have the same underlying numerical type  (floating-point or
>    integer)."
>
> Khronos has further clarified that this also requires the underlying
> types to have the same width, so we can't put a float and a double
> in the same location slot for example. Future versions of the spec will
> be corrected to make this clear.
>
> This patch amends our implementation to account for this restriction.
>
> In the process of doing this, I also noticed that we would attempt
> to check aliasing requirements for record variables (including the test
> for the numerical type) which is not allowed, instead, we should be
> producing a linker error as soon as we see any attempt to do location
> aliasing on a record variable.

Is there a piglit for this? (Which fails without this patch?)

Oh, and you hit it because you stuck the unreachable in there?

> ---
>  src/compiler/glsl/link_varyings.cpp | 41 ++++++++++++++++++++++++++++++-------
>  1 file changed, 34 insertions(+), 7 deletions(-)
>
> diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> index af938611f4..1d17deaffe 100644
> --- a/src/compiler/glsl/link_varyings.cpp
> +++ b/src/compiler/glsl/link_varyings.cpp
> @@ -413,7 +413,7 @@ struct explicit_location_info {
>  };
>
>  static inline unsigned
> -get_numerical_type(const glsl_type *type)
> +get_numerical_sized_type(const glsl_type *type)
>  {
>     /* From the OpenGL 4.6 spec, section 4.4.1 Input Layout Qualifiers, Page 68,
>      * (Location aliasing):
> @@ -421,10 +421,22 @@ get_numerical_type(const glsl_type *type)
>      *    "Further, when location aliasing, the aliases sharing the location
>      *     must have the same underlying numerical type  (floating-point or
>      *     integer)
> +    *
> +    * Khronos has further clarified that this also requires the underlying
> +    * types to have the same width, so we can't put a float and a double
> +    * in the same location slot for example. Future versions of the spec will
> +    * be corrected to make this clear.
>      */
> -   if (type->is_float() || type->is_double())
> +   if (type->is_float())
>        return GLSL_TYPE_FLOAT;
> -   return GLSL_TYPE_INT;
> +   else if (type->is_integer())
> +      return GLSL_TYPE_INT;
> +   else if (type->is_double())
> +      return GLSL_TYPE_DOUBLE;
> +   else if (type->is_integer_64())
> +      return GLSL_TYPE_INT64;

How does a (bindless) sampler/image come across? Do they come out as
->is_integer_64? (I don't think they do.)

> +
> +   unreachable("Type is not numerical");
>  }
>
>  static bool
> @@ -442,14 +454,17 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
>                          gl_shader_stage stage)
>  {
>     unsigned last_comp;
> +   bool is_record;
>     if (type->without_array()->is_record()) {
>        /* The component qualifier can't be used on structs so just treat
>         * all component slots as used.
>         */
>        last_comp = 4;
> +      is_record = true;
>     } else {
>        unsigned dmul = type->without_array()->is_64bit() ? 2 : 1;
>        last_comp = component + type->without_array()->vector_elements * dmul;
> +      is_record = false;
>     }
>
>     while (location < location_limit) {
> @@ -459,8 +474,17 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
>              &explicit_locations[location][comp];
>
>           if (info->var) {
> -            /* Component aliasing is not alloed */
> -            if (comp >= component && comp < last_comp) {
> +            if (is_record) {
> +               /* Disallow location aliasing for record variables */
> +               linker_error(prog,
> +                            "%s shader uses explicit location on record "
> +                            "variable %s that generates location aliasing "
> +                            "for location %u, component %u\n",
> +                            _mesa_shader_stage_to_string(stage),
> +                            var->name, location, comp);
> +               return false;
> +            } else if (comp >= component && comp < last_comp) {
> +               /* Component aliasing is not allowed */
>                 linker_error(prog,
>                              "%s shader has multiple outputs explicitly "
>                              "assigned to location %d and component %d\n",
> @@ -472,7 +496,7 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
>                  * types, interpolation and auxiliary storage
>                  */
>                 if (info->numerical_type !=
> -                   get_numerical_type(type->without_array())) {
> +                   get_numerical_sized_type(type->without_array())) {
>                    linker_error(prog,
>                                 "Varyings sharing the same location must "
>                                 "have the same underlying numerical type. "
> @@ -502,7 +526,10 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
>              }
>           } else if (comp >= component && comp < last_comp) {
>              info->var = var;
> -            info->numerical_type = get_numerical_type(type->without_array());
> +            if (!is_record) {
> +               info->numerical_type =
> +                  get_numerical_sized_type(type->without_array());
> +            }
>              info->interpolation = interpolation;
>              info->centroid = centroid;
>              info->sample = sample;
> --
> 2.11.0
>