[Mesa-dev] [PATCH v2] glsl: enforce invariant conditions for built-in variables

[Ilia Mirkin]

You should be able to check for the slot, which is faster than a strcmp.
Also in the second if, you can hoist the invariant check up to the second
containing if to avoid a bit of unnecessary work.
On May 9, 2016 9:46 AM, "Lars Hamre" <chemecse at gmail.com> wrote:

> v2:
>  - ES version check (Tapani Pälli)
>
> The conditions for which certain built-in special variables
> can be declared invariant were not being checked.
>
> GLSL ES 1.00 specification, Section "Invariance and linkage" says:
>
> For the built-in special variables, gl_FragCoord can
> only be declared invariant if and only if gl_Position is
> declared invariant. Similarly gl_PointCoord can only be
> declared invariant if and only if gl_PointSize is declared
> invariant. It is an error to declare gl_FrontFacing as invariant.
>
> This fixes the following piglit tests in spec/glsl-es-1.00/linker:
> glsl-fcoord-invariant
> glsl-fface-invariant
> glsl-pcoord-invariant
>
> Signed-off-by: Lars Hamre <chemecse at gmail.com>
>
> ---
>
> CC: Tapani Pälli <tapani.palli at intel.com>
>
> NOTE: Someone with access will need to commit this after the
>       review process
>
>  src/compiler/glsl/link_varyings.cpp | 46
> +++++++++++++++++++++++++++++++++++--
>  1 file changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/src/compiler/glsl/link_varyings.cpp
> b/src/compiler/glsl/link_varyings.cpp
> index 34e82c7..2c1f57d 100644
> --- a/src/compiler/glsl/link_varyings.cpp
> +++ b/src/compiler/glsl/link_varyings.cpp
> @@ -352,13 +352,23 @@ cross_validate_outputs_to_inputs(struct
> gl_shader_program *prog,
>     glsl_symbol_table parameters;
>     ir_variable *explicit_locations[MAX_VARYING][4] = { {NULL, NULL} };
>
> +   bool is_gl_position_invariant = false;
> +   bool is_gl_point_size_invariant = false;
> +
>     /* Find all shader outputs in the "producer" stage.
>      */
>     foreach_in_list(ir_instruction, node, producer->ir) {
>        ir_variable *const var = node->as_variable();
>
>        if ((var == NULL) || (var->data.mode != ir_var_shader_out))
> -        continue;
> +         continue;
> +
> +      if (prog->IsES && prog->Version < 300) {
> +         if (!strcmp(var->name, "gl_Position"))
> +            is_gl_position_invariant = var->data.invariant;
> +         if (!strcmp(var->name, "gl_PointSize"))
> +            is_gl_point_size_invariant = var->data.invariant;
> +      }
>
>        if (!var->data.explicit_location
>            || var->data.location < VARYING_SLOT_VAR0)
> @@ -442,7 +452,39 @@ cross_validate_outputs_to_inputs(struct
> gl_shader_program *prog,
>        ir_variable *const input = node->as_variable();
>
>        if ((input == NULL) || (input->data.mode != ir_var_shader_in))
> -        continue;
> +         continue;
> +
> +      /*
> +       * GLSL ES 1.00 specification, Section "Invariance and linkage"
> says:
> +       *
> +       *  "For the built-in special variables, gl_FragCoord can
> +       *  only be declared invariant if and only if gl_Position is
> +       *  declared invariant. Similarly gl_PointCoord can only be
> +       *  declared invariant if and only if gl_PointSize is declared
> +       *  invariant. It is an error to declare gl_FrontFacing as
> invariant."
> +       */
> +      if (prog->IsES && prog->Version < 300) {
> +         if (!strcmp(input->name, "gl_FrontFacing") &&
> +               input->data.invariant) {
> +            linker_error(prog,
> +                         "gl_FrontFacing cannot be declared invariant");
> +            return;
> +         } else if (!strcmp(input->name, "gl_FragCoord") &&
> +                    input->data.invariant &&
> +                    !is_gl_position_invariant) {
> +            linker_error(prog,
> +                         "gl_FragCoord cannot be declared invariant "
> +                         "unless gl_Position is also invariant");
> +            return;
> +         } else if (!strcmp(input->name, "gl_PointCoord") &&
> +                    input->data.invariant &&
> +                    !is_gl_point_size_invariant) {
> +            linker_error(prog,
> +                         "gl_PointCoord cannot be declared invariant "
> +                         "unless gl_PointSize is also invariant");
> +            return;
> +         }
> +      }
>
>        if (strcmp(input->name, "gl_Color") == 0 && input->data.used) {
>           const ir_variable *const front_color =
> --
> 2.5.5
>
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