[Mesa-dev] [PATCH] glsl: remove interpolateAt* instructions for demoted inputs

[Connor Abbott]

Since demoted inputs become global variables, wouldn't it be more
efficient to simply turn it into a straight assignment? Then the
backend wouldn't have to initialize it to a constant (since it would
be undefined).

On Fri, Sep 9, 2016 at 10:06 AM, Marek Olšák <maraeo at gmail.com> wrote:
> From: Marek Olšák <marek.olsak at amd.com>
>
> This fixes 8 fs-interpolateat* piglit crashes on radeonsi, because it can't
> handle non-input operands in interpolateAt*.
> ---
>  src/compiler/glsl/link_varyings.cpp |  5 +++++
>  src/compiler/glsl/opt_algebraic.cpp | 10 ++++++++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> index 1fad310..85ca044 100644
> --- a/src/compiler/glsl/link_varyings.cpp
> +++ b/src/compiler/glsl/link_varyings.cpp
> @@ -586,20 +586,25 @@ remove_unused_shader_inputs_and_outputs(bool is_separate_shader_object,
>
>        if (var == NULL || var->data.mode != int(mode))
>           continue;
>
>        /* A shader 'in' or 'out' variable is only really an input or output if
>         * its value is used by other shader stages. This will cause the
>         * variable to have a location assigned.
>         */
>        if (var->data.is_unmatched_generic_inout && !var->data.is_xfb_only) {
>           assert(var->data.mode != ir_var_temporary);
> +
> +         /* Assign zeros to demoted inputs to allow more optimizations. */
> +         if (var->data.mode == ir_var_shader_in && !var->constant_value)
> +            var->constant_value = ir_constant::zero(var, var->type);
> +
>           var->data.mode = ir_var_auto;
>        }
>     }
>
>     /* Eliminate code that is now dead due to unused inputs/outputs being
>      * demoted.
>      */
>     while (do_dead_code(sh->ir, false))
>        ;
>
> diff --git a/src/compiler/glsl/opt_algebraic.cpp b/src/compiler/glsl/opt_algebraic.cpp
> index f5858c8..2829a78 100644
> --- a/src/compiler/glsl/opt_algebraic.cpp
> +++ b/src/compiler/glsl/opt_algebraic.cpp
> @@ -954,20 +954,30 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
>        }
>        break;
>
>     case ir_triop_csel:
>        if (is_vec_one(op_const[0]))
>          return ir->operands[1];
>        if (is_vec_zero(op_const[0]))
>          return ir->operands[2];
>        break;
>
> +   /* Remove interpolateAt* instructions for demoted inputs. They are
> +    * assigned a constant expression to facilitate this.
> +    */
> +   case ir_unop_interpolate_at_centroid:
> +   case ir_binop_interpolate_at_offset:
> +   case ir_binop_interpolate_at_sample:
> +      if (op_const[0])
> +         return ir->operands[0];
> +      break;
> +
>     default:
>        break;
>     }
>
>     return ir;
>  }
>
>  void
>  ir_algebraic_visitor::handle_rvalue(ir_rvalue **rvalue)
>  {
> --
> 2.7.4
>
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