[Mesa-dev] [PATCH] glsl: remove redundant function inout assignments

[Ilia Mirkin]

On Sun, Nov 1, 2015 at 3:33 AM, Timothy Arceri <t_arceri at yahoo.com.au> wrote:
> Handles the case with function inout params where array elements
> do an assignment to themselves e.g.
>
>  void array_mod(inout int b[2])
>  {
>     b[0] = int(2);
>     b[1] = b[1];
>  }
>
>  Fixes assert in nir for:
>  ES31-CTS.arrays_of_arrays.InteractionFunctionCalls2
>
> https://bugs.freedesktop.org/show_bug.cgi?id=92588
> ---
>  src/glsl/opt_copy_propagation_elements.cpp | 46 ++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>
>  Piglit test: https://patchwork.freedesktop.org/patch/63355/
>
> diff --git a/src/glsl/opt_copy_propagation_elements.cpp b/src/glsl/opt_copy_propagation_elements.cpp
> index 353a5c6..a62b625 100644
> --- a/src/glsl/opt_copy_propagation_elements.cpp
> +++ b/src/glsl/opt_copy_propagation_elements.cpp
> @@ -439,6 +439,8 @@ ir_copy_propagation_elements_visitor::kill(kill_entry *k)
>  /**
>   * Adds directly-copied channels between vector variables to the available
>   * copy propagation list.
> + *
> + * Also tidy up redundant function inout assignments while we are here.
>   */
>  void
>  ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
> @@ -450,6 +452,50 @@ ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
>     if (ir->condition)
>        return;
>
> +   /* Handle a corner case with function inout params where array elements
> +    * do an assignment to themselves e.g.
> +    *
> +    * void array_mod(inout int b[2])
> +    * {
> +    *    b[0] = int(2);
> +    *    b[1] = b[1];
> +    * }

What if you have like

array_mod(inout vec2 b[2]) {
  b[1] = b[1].xy;
or
  b[1] = b[1].yx;
}

IOW, why is this case so special?

> +    */
> +   ir_rvalue *rhs_array = ir->rhs;
> +   ir_rvalue *lhs_array = ir->lhs;
> +   if (lhs_array->as_dereference_array() &&
> +       rhs_array->as_dereference_array()) {
> +      /* Check arrays are indexed by a const and match otherwise return */
> +      while (rhs_array->as_dereference_array() &&
> +             lhs_array->as_dereference_array()) {
> +
> +         ir_dereference_array *rhs_deref_array =
> +            rhs_array->as_dereference_array();
> +         ir_dereference_array *lhs_deref_array =
> +            lhs_array->as_dereference_array();
> +
> +         ir_constant *lhs_ai_const =
> +            lhs_deref_array->array_index->as_constant();
> +         ir_constant *rhs_ai_const =
> +            rhs_deref_array->array_index->as_constant();
> +         if (lhs_ai_const == NULL || rhs_ai_const == NULL ||
> +             lhs_ai_const->value.i[0] != rhs_ai_const->value.i[0])
> +            return;
> +         lhs_array = lhs_deref_array->array;
> +         rhs_array = rhs_deref_array->array;
> +      }
> +
> +      ir_dereference_variable *lhs_var = lhs_array->as_dereference_variable();
> +      ir_dereference_variable *rhs_var = rhs_array->as_dereference_variable();
> +      if(lhs_var && rhs_var && lhs_var->var == rhs_var->var){

spaces please

> +        /* Removing the assignment now would mess up the loop iteration
> +         * calling us.  Just flag it to not execute, and someone else
> +         * will clean up the mess.
> +         */
> +        ir->condition = new(ralloc_parent(ir)) ir_constant(false);

I thought that the allocator was smart and you could just do new (ir)
ir_constant(false). e.g.

src/glsl/lower_jumps.cpp:            new (ir) ir_constant(true)));

> +      }
> +   }
> +
>     ir_dereference_variable *lhs = ir->lhs->as_dereference_variable();
>     if (!lhs || !(lhs->type->is_scalar() || lhs->type->is_vector()))
>        return;
> --
> 2.4.3
>
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