[Mesa-dev] [v2 PATCH 09/16] glsl: Optimize clamp(x, 0, 1) as saturate(x)

[Matt Turner]

On Mon, Jul 7, 2014 at 6:57 AM, Abdiel Janulgue
<abdiel.janulgue at linux.intel.com> wrote:
> v2: Check that the base type is float (Ian Romanick)
>
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue at linux.intel.com>
> ---
>  src/glsl/opt_algebraic.cpp | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
> index ac7514a..2ad561c 100644
> --- a/src/glsl/opt_algebraic.cpp
> +++ b/src/glsl/opt_algebraic.cpp
> @@ -614,6 +614,40 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
>
>        break;
>
> +   case ir_binop_min:
> +   case ir_binop_max:
> +      if (ir->type->base_type != GLSL_TYPE_FLOAT)
> +         break;
> +      /* Replace min(max) operations and its commutative combinations with
> +       * a saturate operation
> +       */
> +      for (int op = 0; op < 2; op++) {
> +         ir_expression *minmax = op_expr[op];
> +         ir_constant *outer_const = op_const[(op == 0) ? 1 : 0];

We use (1 - op) in other places in opt_algebraic. (Same comment below)

> +         ir_expression_operation op_cond = (ir->operation == ir_binop_max) ?
> +            ir_binop_min : ir_binop_max;
> +
> +         if (!minmax || !outer_const || (minmax->operation != op_cond))
> +            continue;
> +
> +         /* Found a min/max operation. Now try to see if its operands
> +          * meet our conditions that we can do just a single saturate operation
> +          */
> +         for (int minmax_op = 0; minmax_op < 2; minmax_op++) {
> +            ir_rvalue *inner_val_a = minmax->operands[minmax_op];
> +            ir_rvalue *inner_val_b = minmax->operands[(minmax_op == 0) ? 1 : 0];
> +
> +            if (!inner_val_a || !inner_val_b)
> +               continue;
> +
> +            /* Found a min (max(x, 0), 1.0) */

This comment tripped me up for a second. This really means that you've
found either

  - min(max(x, 0.0), 1.0); or
  - max(min(x, 1.0), 0.0)

Change the comment to something that says either of these are
acceptable. (Also make the spacing consistent. There's a space after
the min. And Make the floating point literals consistent with .0 on
both)