[Mesa-dev] [PATCH 1/2] nir: optimize min(min(a, b), c) to min3(a, b, c) under an option

[Timothy Arceri]

On 31/05/18 19:26, Samuel Pitoiset wrote:
> 
> 
> On 05/31/2018 11:25 AM, Bas Nieuwenhuizen wrote:
>> On Thu, May 31, 2018 at 11:13 AM, Samuel Pitoiset
>> <samuel.pitoiset at gmail.com> wrote:
>>>
>>>
>>> On 05/31/2018 01:55 AM, Timothy Arceri wrote:
>>>>
>>>> On 31/05/18 03:06, Samuel Pitoiset wrote:
>>>>>
>>>>> Similar for max().
>>>>>
>>>>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>>>>> ---
>>>>>    src/compiler/nir/nir.h                | 3 +++
>>>>>    src/compiler/nir/nir_opt_algebraic.py | 8 ++++++++
>>>>>    2 files changed, 11 insertions(+)
>>>>>
>>>>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>>>>> index f6086bd6c0..04991b7d04 100644
>>>>> --- a/src/compiler/nir/nir.h
>>>>> +++ b/src/compiler/nir/nir.h
>>>>> @@ -1897,6 +1897,9 @@ typedef struct nir_shader_compiler_options {
>>>>>       /* lower b2f to iand */
>>>>>       bool lower_b2f;
>>>>> +   /* lower min(min(a, b), c) to min3(a, b, c) (same for max()). */
>>>>> +   bool lower_minmax3;
>>>>> +
>>>>>       /* Does the native fdot instruction replicate its result for 
>>>>> four
>>>>>        * components?  If so, then opt_algebraic_late will turn all 
>>>>> fdotN
>>>>>        * instructions into fdot_replicatedN instructions.
>>>>> diff --git a/src/compiler/nir/nir_opt_algebraic.py
>>>>> b/src/compiler/nir/nir_opt_algebraic.py
>>>>> index 909ea3daf4..1d67e2d88c 100644
>>>>> --- a/src/compiler/nir/nir_opt_algebraic.py
>>>>> +++ b/src/compiler/nir/nir_opt_algebraic.py
>>>>> @@ -224,6 +224,14 @@ optimizations = [
>>>>>       (('imax', a, a), a),
>>>>>       (('umin', a, a), a),
>>>>>       (('umax', a, a), a),
>>>>> +
>>>>> +   (('fmin', ('fmin', a, b), c), ('fmin3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>> +   (('imin', ('imin', a, b), c), ('imin3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>> +   (('umin', ('umin', a, b), c), ('umin3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>> +   (('fmax', ('fmax', a, b), c), ('fmax3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>> +   (('imax', ('imax', a, b), c), ('imax3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>> +   (('umax', ('umax', a, b), c), ('umax3', a, b, c),
>>>>> 'options->lower_minmax3'),
>>>>
>>>>
>>>> These look like they would be better suited in late_optimizations 
>>>> rather
>>>> than optimizations?
>>>
>>>
>>> Totals from affected shaders:
>>> SGPRS: 104 -> 104 (0.00 %)
>>> VGPRS: 64 -> 64 (0.00 %)
>>> Spilled SGPRs: 0 -> 0 (0.00 %)
>>> Spilled VGPRs: 0 -> 0 (0.00 %)
>>> Private memory VGPRs: 0 -> 0 (0.00 %)
>>> Scratch size: 0 -> 0 (0.00 %) dwords per thread
>>> Code Size: 4652 -> 4644 (-0.17 %) bytes
>>> LDS: 4 -> 4 (0.00 %) blocks
>>> Max Waves: 24 -> 24 (0.00 %)
>>> Wait states: 0 -> 0 (0.00 %)
>>>
>>> When moved to late_optimizations.
>>
>> Is that compared to no min3/max3 lowering at all or compared to doing
>> those non-late?
> 
> Compared to "default" for both.

It might be worth looking at the difference in the shaders. It would be 
interesting to understand why we need to do this early and if it means 
there are other opportunities for lowering these that this pattern 
doesn't find.

> 
>>>
>>>
>>>>
>>>>
>>>>> +
>>>>>       (('fmin', a, ('fneg', a)), ('fneg', ('fabs', a))),
>>>>>       (('imin', a, ('ineg', a)), ('ineg', ('iabs', a))),
>>>>>       (('fmin', a, ('fneg', ('fabs', a))), ('fneg', ('fabs', a))),
>>>>>
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