[Mesa-dev] [PATCH v2] glsl/linker: Allow unused in blocks which are not declated on previous stage

[Alejandro Piñeiro]

CCing Timothy just in case he still thinks that the original comment
should remain as it is. In any case, it looks to me, so:

Reviewed-by: Alejandro Piñeiro <apinheiro at igalia.com>


On 23/08/18 12:12, vadym.shovkoplias wrote:
> From Section 4.3.4 (Inputs) of the GLSL 1.50 spec:
>
>     "Only the input variables that are actually read need to be written
>      by the previous stage; it is allowed to have superfluous
>      declarations of input variables."
>
> Fixes:
>     * interstage-multiple-shader-objects.shader_test
>
> v2:
>   Update comment in ir.h since the usage of "used" field
>   has been extended.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101247
> Signed-off-by: Vadym Shovkoplias <vadym.shovkoplias at globallogic.com>
> ---
>  src/compiler/glsl/ir.h                      | 4 ++--
>  src/compiler/glsl/link_interface_blocks.cpp | 8 +++++++-
>  2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/src/compiler/glsl/ir.h b/src/compiler/glsl/ir.h
> index 67b38f48ef..d05d1998a5 100644
> --- a/src/compiler/glsl/ir.h
> +++ b/src/compiler/glsl/ir.h
> @@ -667,8 +667,8 @@ public:
>         * variable has been used.  For example, it is an error to redeclare a
>         * variable as invariant after it has been used.
>         *
> -       * This is only maintained in the ast_to_hir.cpp path, not in
> -       * Mesa's fixed function or ARB program paths.
> +       * This is maintained in the ast_to_hir.cpp path and during linking,
> +       * but not in Mesa's fixed function or ARB program paths.
>         */
>        unsigned used:1;
>  
> diff --git a/src/compiler/glsl/link_interface_blocks.cpp b/src/compiler/glsl/link_interface_blocks.cpp
> index e5eca9460e..801fbcd5d9 100644
> --- a/src/compiler/glsl/link_interface_blocks.cpp
> +++ b/src/compiler/glsl/link_interface_blocks.cpp
> @@ -417,9 +417,15 @@ validate_interstage_inout_blocks(struct gl_shader_program *prog,
>         * write to any of the pre-defined outputs (e.g. if the vertex shader
>         * does not write to gl_Position, etc), which is allowed and results in
>         * undefined behavior.
> +       *
> +       * From Section 4.3.4 (Inputs) of the GLSL 1.50 spec:
> +       *
> +       *    "Only the input variables that are actually read need to be written
> +       *     by the previous stage; it is allowed to have superfluous
> +       *     declarations of input variables."
>         */
>        if (producer_def == NULL &&
> -          !is_builtin_gl_in_block(var, consumer->Stage)) {
> +          !is_builtin_gl_in_block(var, consumer->Stage) && var->data.used) {
>           linker_error(prog, "Input block `%s' is not an output of "
>                        "the previous stage\n", var->get_interface_type()->name);
>           return;