[Mesa-dev] [PATCH 04/12] glsl: Lower ir_binop_vector_extract to swizzle

[Kenneth Graunke]

On 04/08/2013 03:24 PM, Ian Romanick wrote:
> From: Ian Romanick <ian.d.romanick at intel.com>
>
> Lower ir_binop_vector_extract with a constant index to a swizzle.  This
> is exactly like ir_dereference_array of a vector with a constant index.
>
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> ---
>   src/glsl/lower_vec_index_to_swizzle.cpp | 45 +++++++++++++++++++++++++++++++++
>   1 file changed, 45 insertions(+)
>
> diff --git a/src/glsl/lower_vec_index_to_swizzle.cpp b/src/glsl/lower_vec_index_to_swizzle.cpp
> index 264d6dc..ad09dd2 100644
> --- a/src/glsl/lower_vec_index_to_swizzle.cpp
> +++ b/src/glsl/lower_vec_index_to_swizzle.cpp
> @@ -47,6 +47,7 @@ public:
>      }
>
>      ir_rvalue *convert_vec_index_to_swizzle(ir_rvalue *val);
> +   ir_rvalue *convert_vector_extract_to_swizzle(ir_rvalue *val);
>
>      virtual ir_visitor_status visit_enter(ir_expression *);
>      virtual ir_visitor_status visit_enter(ir_swizzle *);
> @@ -98,6 +99,40 @@ ir_vec_index_to_swizzle_visitor::convert_vec_index_to_swizzle(ir_rvalue *ir)
>      return new(ctx) ir_swizzle(deref->array, i, 0, 0, 0, 1);
>   }
>
> +ir_rvalue *
> +ir_vec_index_to_swizzle_visitor::convert_vector_extract_to_swizzle(ir_rvalue *ir)
> +{
> +   ir_expression *const expr = ir->as_expression();
> +   if (expr == NULL || expr->operation != ir_binop_vector_extract)
> +      return ir;
> +
> +   ir_constant *const idx = expr->operands[1]->constant_expression_value();
> +   if (idx == NULL)
> +      return ir;
> +
> +   void *ctx = ralloc_parent(ir);
> +   this->progress = true;
> +
> +   /* Page 40 of the GLSL 1.20 spec says:
> +    *
> +    *     "When indexing with non-constant expressions, behavior is undefined
> +    *     if the index is negative, or greater than or equal to the size of
> +    *     the vector."
> +    *
> +    * The quoted spec text mentions non-constant expressions, but this code
> +    * operates on constants.  These constants are the result of non-constant
> +    * expressions that have been optimized to constants.  The common case here
> +    * is a loop counter from an unrolled loop that is used to index a vector.
> +    *
> +    * The ir_swizzle constructor gets angry if the index is negative or too
> +    * large.  For simplicity sake, just clamp the index to [0, size-1].
> +    */
> +   const int i = MIN2(MAX2(idx->value.i[0], 0),
> +		      ((int) expr->operands[0]->type->vector_elements - 1));
> +
> +   return new(ctx) ir_swizzle(expr->operands[0], i, 0, 0, 0, 1);
> +}
> +
>   ir_visitor_status
>   ir_vec_index_to_swizzle_visitor::visit_enter(ir_expression *ir)
>   {
> @@ -105,6 +140,7 @@ ir_vec_index_to_swizzle_visitor::visit_enter(ir_expression *ir)
>
>      for (i = 0; i < ir->get_num_operands(); i++) {
>         ir->operands[i] = convert_vec_index_to_swizzle(ir->operands[i]);
> +      ir->operands[i] = convert_vector_extract_to_swizzle(ir->operands[i]);
>      }
>
>      return visit_continue;
> @@ -127,6 +163,7 @@ ir_vec_index_to_swizzle_visitor::visit_enter(ir_assignment *ir)
>   {
>      ir->set_lhs(convert_vec_index_to_swizzle(ir->lhs));
>      ir->rhs = convert_vec_index_to_swizzle(ir->rhs);
> +   ir->rhs = convert_vector_extract_to_swizzle(ir->rhs);
>
>      return visit_continue;
>   }
> @@ -140,6 +177,12 @@ ir_vec_index_to_swizzle_visitor::visit_enter(ir_call *ir)
>
>         if (new_param != param) {
>   	 param->replace_with(new_param);
> +      } else {
> +	 new_param = convert_vec_index_to_swizzle(param);

This is wrong.  You want convert_vector_extract_to_swizzle(param). 
Clearly, the intention is to do both, and instead you're calling the old 
method twice.

> +
> +	 if (new_param != param) {
> +	    param->replace_with(new_param);
> +	 }
>         }
>      }
>
> @@ -151,6 +194,7 @@ ir_vec_index_to_swizzle_visitor::visit_enter(ir_return *ir)
>   {
>      if (ir->value) {
>         ir->value = convert_vec_index_to_swizzle(ir->value);
> +      ir->value = convert_vector_extract_to_swizzle(ir->value);
>      }
>
>      return visit_continue;
> @@ -160,6 +204,7 @@ ir_visitor_status
>   ir_vec_index_to_swizzle_visitor::visit_enter(ir_if *ir)
>   {
>      ir->condition = convert_vec_index_to_swizzle(ir->condition);
> +   ir->condition = convert_vector_extract_to_swizzle(ir->condition);
>
>      return visit_continue;
>   }
>