[Mesa-dev] [PATCH 09/16] glsl: Add sqrt, rsq, exp, exp2 to get_range

[Ian Romanick]

On 11/16/2014 05:51 PM, Thomas Helland wrote:
> Also handle undefined behaviour for sqrt(x) where x < 0
> and rsq(x) where x <= 0.
> 
> This gives us some reduction in instruction count on some
> Dungeon Defenders shaders as they are doing: max(exp(x), 0)
> ---
>  src/glsl/opt_minmax.cpp | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/src/glsl/opt_minmax.cpp b/src/glsl/opt_minmax.cpp
> index a48d4d8..1aa4611 100644
> --- a/src/glsl/opt_minmax.cpp
> +++ b/src/glsl/opt_minmax.cpp
> @@ -293,6 +293,23 @@ get_range(ir_rvalue *rval)
>              high = larger_constant(r0.high, abs(r0.low)->constant_expression_value());
>           return minmax_range(low, high);
>  
> +      case ir_unop_sqrt:
> +      case ir_unop_rsq:
> +      case ir_unop_exp:
> +      case ir_unop_exp2:
> +         r0 = get_range(expr->operands[0]);
> +         if (expr->operation == ir_unop_sqrt &&
> +             is_less_than_zero(r0.high))
> +            high = new(mem_ctx) ir_constant(0.0f);

A blank line here...

> +         if (expr->operation == ir_unop_rsq &&
> +             is_less_than_or_equal_zero(r0.high))
> +            high = new(mem_ctx) ir_constant(0.0f);

...and here makes the code much easier to read.

These two blocks calculate high, but it's never used.  Is that intentional?

> +         /* TODO: If we know, i.e, the lower range of the operand
> +          * we can calculate the lower range
> +          */
> +         low = new(mem_ctx) ir_constant(0.0f);
> +         return minmax_range(low, NULL);
> +
>        case ir_unop_sin:
>        case ir_unop_sin_reduced:
>        case ir_unop_cos:
>