[Mesa-dev] [PATCH 5/6] glsl: don't sort varying in separate shader mode

[Tapani Pälli]

Reviewed-by: Tapani Pälli <tapani.palli at intel.com>

On 11/25/2015 11:54 AM, Timothy Arceri wrote:
> From: Gregory Hainaut <gregory.hainaut at gmail.com>
>
> This fixes an issue where the addition of the FLAT qualifier in
> varying_matches::record() can break the expected varying order.
>
> It also avoids a future issue with the relaxing of interpolation
> qualifier matching constraints in GLSL 4.50.
>
> V2: (by Timothy Arceri)
> * reworked comment slightly
>
> Signed-off-by: Gregory Hainaut <gregory.hainaut at gmail.com>
> Reviewed-by: Timothy Arceri <timothy.arceri at collabora.com>
> ---
>   src/glsl/link_varyings.cpp | 38 ++++++++++++++++++++++++++++++++------
>   1 file changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
> index ac2755f..71750d1 100644
> --- a/src/glsl/link_varyings.cpp
> +++ b/src/glsl/link_varyings.cpp
> @@ -766,7 +766,7 @@ public:
>                      gl_shader_stage consumer_stage);
>      ~varying_matches();
>      void record(ir_variable *producer_var, ir_variable *consumer_var);
> -   unsigned assign_locations(uint64_t reserved_slots);
> +   unsigned assign_locations(uint64_t reserved_slots, bool separate_shader);
>      void store_locations() const;
>
>   private:
> @@ -988,11 +988,36 @@ varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
>    * passed to varying_matches::record().
>    */
>   unsigned
> -varying_matches::assign_locations(uint64_t reserved_slots)
> +varying_matches::assign_locations(uint64_t reserved_slots, bool separate_shader)
>   {
> -   /* Sort varying matches into an order that makes them easy to pack. */
> -   qsort(this->matches, this->num_matches, sizeof(*this->matches),
> -         &varying_matches::match_comparator);
> +   /* We disable varying sorting for separate shader programs for the
> +    * following reasons:
> +    *
> +    * 1/ All programs must sort the code in the same order to guarantee the
> +    *    interface matching. However varying_matches::record() will change the
> +    *    interpolation qualifier of some stages.
> +    *
> +    * 2/ GLSL version 4.50 removes the matching constrain on the interpolation
> +    *    qualifier.
> +    *
> +    * From Section 4.5 (Interpolation Qualifiers) of the GLSL 4.40 spec:
> +    *
> +    *    "The type and presence of interpolation qualifiers of variables with
> +    *    the same name declared in all linked shaders for the same cross-stage
> +    *    interface must match, otherwise the link command will fail.
> +    *
> +    *    When comparing an output from one stage to an input of a subsequent
> +    *    stage, the input and output don't match if their interpolation
> +    *    qualifiers (or lack thereof) are not the same."
> +    *
> +    *    "It is a link-time error if, within the same stage, the interpolation
> +    *    qualifiers of variables of the same name do not match."
> +    */
> +   if (!separate_shader) {
> +      /* Sort varying matches into an order that makes them easy to pack. */
> +      qsort(this->matches, this->num_matches, sizeof(*this->matches),
> +            &varying_matches::match_comparator);
> +   }
>
>      unsigned generic_location = 0;
>      unsigned generic_patch_location = MAX_VARYING*4;
> @@ -1592,7 +1617,8 @@ assign_varying_locations(struct gl_context *ctx,
>         reserved_varying_slot(producer, ir_var_shader_out) |
>         reserved_varying_slot(consumer, ir_var_shader_in);
>
> -   const unsigned slots_used = matches.assign_locations(reserved_slots);
> +   const unsigned slots_used = matches.assign_locations(reserved_slots,
> +                                                        prog->SeparateShader);
>      matches.store_locations();
>
>      for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
>