[Mesa-dev] [v2 PATCH 10/16] glsl: Optimize clamp(x, 0.0, b), where b < 1.0 as min(saturate(x), b)

[Abdiel Janulgue]

On 08.07.2014 12:37, Abdiel Janulgue wrote:
> 
> On 07.07.2014 20:25, Matt Turner wrote:
>> On Mon, Jul 7, 2014 at 6:57 AM, Abdiel Janulgue
>> <abdiel.janulgue at linux.intel.com> wrote:
>>> v2: - Output min(saturate(x),b) instead of saturate(min(x,b)) suggested by Ilia Mirkin
>>>     - Make sure we do component-wise comparison for vectors (Ian Romanick)
>>>
>>> Signed-off-by: Abdiel Janulgue <abdiel.janulgue at linux.intel.com>
>>> ---
>>>  src/glsl/opt_algebraic.cpp | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
>>> index 2ad561c..bcda7a9 100644
>>> --- a/src/glsl/opt_algebraic.cpp
>>> +++ b/src/glsl/opt_algebraic.cpp
>>> @@ -643,6 +643,16 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
>>>              /* Found a min (max(x, 0), 1.0) */
>>>              if (outer_const->is_one() && inner_val_a->is_zero())
>>>                 return saturate(inner_val_b);
>>> +
>>> +            unsigned component = 0;
>>> +            for (int c = 0; c < outer_const->type->vector_elements; c++) {
>>> +               if (outer_const->get_float_component(c) < 1.0f)
>>> +                  component++;
>>> +            }
>>> +            /* Found a min (max(x, 0.0) b), where b < 1.0 */
>>
>> Is this case the only thing it finds?
>>
>> Does it find max(min(x, b), 0.0)?
> 
> Unfortunately, you are right. The detection only works if the inner
> constant is zero. I'll fix this in the next revision
> 
>>
>>> +            if ((component == outer_const->type->vector_elements) &&
>>> +                inner_val_b->is_zero())
>>> +               return expr(ir_binop_min, saturate(inner_val_a), outer_const);
>>
>> It seems like it would incorrectly recognize max(min(x, 0.0), b).
>>
> 
> This one it would correctly recognize.

Actually no, this one actually does not work either. Fix coming up!