On Sat, 2015-01-03 at 20:18 +0100, Thomas Helland wrote:
> V2: Add some air for readability
> Use the new IS_CONSTANT macro
> Combine if-blocks for reduced code-duplication
> Split out into separate function for reuse later
> ---
> src/glsl/opt_minmax.cpp | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/src/glsl/opt_minmax.cpp b/src/glsl/opt_minmax.cpp
> index 4153a48..e4aa677 100644
> --- a/src/glsl/opt_minmax.cpp
> +++ b/src/glsl/opt_minmax.cpp
> @@ -300,6 +300,34 @@ resolv_add_range(minmax_range r0, minmax_range r1)
> return minmax_range(low, high);
> }
>
> +/* Takes the range of the operands in a mul-operation as parameters
> + * and uses this to solve the range of the mul-operation itself.
> + */
> +static minmax_range
> +resolv_mul_range(minmax_range r0, minmax_range r1)
> +{
> + ir_constant *low = NULL;
> + ir_constant *high = NULL;
> +
> + // Both are positive, or both are negative, result is positive
> + if ((IS_CONSTANT(r0.low, >=, 0.0f) && IS_CONSTANT(r1.low, >=, 0.0f)) ||
> + (IS_CONSTANT(r0.high, <=, 0.0f) && IS_CONSTANT(r1.high, <=, 0.0f))) {
> + low = mul(r0.low, r1.low)->constant_expression_value();
> + if (r0.high && r1.high)
> + high = mul(r0.high, r1.high)->constant_expression_value();
> + }
Hi,
I think that this one is wrong: imagine the case where r0.low,high and
r1.low,high are negative, for example [-2,-1] [-4,-3].
In this case, the resulting range for the multiplication is bound in [3,
8] = [high*high, low*low], not [low*low, high*high].
- Bruno
> +
> + // r0 pos and r1 neg, or r0 neg and r1 pos, result is negative
> + if ((IS_CONSTANT(r0.low, >=, 0.0f) && IS_CONSTANT(r1.high, <=, 0.0f)) ||
> + (IS_CONSTANT(r1.low, >=, 0.0f) && IS_CONSTANT(r0.high, <=, 0.0f))) {
> + high = mul(r0.low, r1.high)->constant_expression_value();
> + if (r0.high && r1.low)
> + low = mul(r0.high, r1.low)->constant_expression_value();
> + }
> +
> + return minmax_range(low, high);
> +}
> +
> static minmax_range
> get_range(ir_rvalue *rval)
> {
> @@ -389,6 +417,11 @@ get_range(ir_rvalue *rval)
> r1 = get_range(expr->operands[1]);
> return combine_range(r0, r1, expr->operation == ir_binop_min);
>
> + case ir_binop_mul:
> + r0 = get_range(expr->operands[0]);
> + r1 = get_range(expr->operands[1]);
> + return resolv_mul_range(r0, r1);
> +
> default:
> break;
> }
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