[Mesa-dev] [RFC]: gallium: add new float comparison opcodes returning integer booleans

[Christoph Bumiller]

On 09.08.2013 20:42, Roland Scheidegger wrote:
> This is a proposal for new comparison instructions, as the old ones
> don't really fit modern (graphic or opencl I guess for that matter)
> languages well.
> If you've got objections, think the naming is crazy or whatnot I'm open
> for suggestions :-). I would think this is not just a much better fit
> for d3d10/glsl but for hw as well.

I think current hardware can do both, and as for the names, I'm fine
with the prefixed ones being the "modern" opcodes (prefix referring to
the source type in both cases) and the ones that are named exactly like
the legacy opcodes behaving like the legacy ones.

Otoh newcomers might get confused and think the F prefix meaning that
they should return a float, we had a similar issue with legacy-KIL and
KILP-condition-is-predicate-if-any (and I just need to say again I'd
have preferred to keep the name KIL and rename KILP to DISCARD), but
seriously, the opcodes are documented so it should be no trouble to
figure out what they do (ok in practice that doesn't always work since
we sometimes like to read what we expect instead of what's actually
written).

> Roland
>
> Am 09.08.2013 20:40, schrieb sroland at vmware.com:
>> From: Roland Scheidegger <sroland at vmware.com>
>>
>> The old float comparison opcodes always return floats 0.0 and 1.0 (clarified
>> in docs these were really floats, was always the case) for legacy graphics.
>> But everybody else (opengl,opencl,d3d10) just has to work around their
>> return results (converting the returned float back to int/boolean).
>> ---
>>  src/gallium/docs/source/tgsi.rst |   84 ++++++++++++++++++++++++++++++--------
>>  1 file changed, 68 insertions(+), 16 deletions(-)
>>
>> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
>> index 949ad89..b7c40cf 100644
>> --- a/src/gallium/docs/source/tgsi.rst
>> +++ b/src/gallium/docs/source/tgsi.rst
>> @@ -512,13 +512,13 @@ This instruction replicates its result.
>>  
>>  .. math::
>>  
>> -  dst.x = (src0.x == src1.x) ? 1 : 0
>> +  dst.x = (src0.x == src1.x) ? 1.0F : 0.0F
>>  
>> -  dst.y = (src0.y == src1.y) ? 1 : 0
>> +  dst.y = (src0.y == src1.y) ? 1.0F : 0.0F
>>  
>> -  dst.z = (src0.z == src1.z) ? 1 : 0
>> +  dst.z = (src0.z == src1.z) ? 1.0F : 0.0F
>>  
>> -  dst.w = (src0.w == src1.w) ? 1 : 0
>> +  dst.w = (src0.w == src1.w) ? 1.0F : 0.0F
>>  
>>  
>>  .. opcode:: SFL - Set On False
>> @@ -538,13 +538,13 @@ This instruction replicates its result.
>>  
>>  .. math::
>>  
>> -  dst.x = (src0.x > src1.x) ? 1 : 0
>> +  dst.x = (src0.x > src1.x) ? 1.0F : 0.0F
>>  
>> -  dst.y = (src0.y > src1.y) ? 1 : 0
>> +  dst.y = (src0.y > src1.y) ? 1.0F : 0.0F
>>  
>> -  dst.z = (src0.z > src1.z) ? 1 : 0
>> +  dst.z = (src0.z > src1.z) ? 1.0F : 0.0F
>>  
>> -  dst.w = (src0.w > src1.w) ? 1 : 0
>> +  dst.w = (src0.w > src1.w) ? 1.0F : 0.0F
>>  
>>  
>>  .. opcode:: SIN - Sine
>> @@ -560,26 +560,26 @@ This instruction replicates its result.
>>  
>>  .. math::
>>  
>> -  dst.x = (src0.x <= src1.x) ? 1 : 0
>> +  dst.x = (src0.x <= src1.x) ? 1.0F : 0.0F
>>  
>> -  dst.y = (src0.y <= src1.y) ? 1 : 0
>> +  dst.y = (src0.y <= src1.y) ? 1.0F : 0.0F
>>  
>> -  dst.z = (src0.z <= src1.z) ? 1 : 0
>> +  dst.z = (src0.z <= src1.z) ? 1.0F : 0.0F
>>  
>> -  dst.w = (src0.w <= src1.w) ? 1 : 0
>> +  dst.w = (src0.w <= src1.w) ? 1.0F : 0.0F
>>  
>>  
>>  .. opcode:: SNE - Set On Not Equal
>>  
>>  .. math::
>>  
>> -  dst.x = (src0.x != src1.x) ? 1 : 0
>> +  dst.x = (src0.x != src1.x) ? 1.0F : 0.0F
>>  
>> -  dst.y = (src0.y != src1.y) ? 1 : 0
>> +  dst.y = (src0.y != src1.y) ? 1.0F : 0.0F
>>  
>> -  dst.z = (src0.z != src1.z) ? 1 : 0
>> +  dst.z = (src0.z != src1.z) ? 1.0F : 0.0F
>>  
>> -  dst.w = (src0.w != src1.w) ? 1 : 0
>> +  dst.w = (src0.w != src1.w) ? 1.0F : 0.0F
>>  
>>  
>>  .. opcode:: STR - Set On True
>> @@ -1325,6 +1325,19 @@ Support for these opcodes indicated by PIPE_SHADER_CAP_INTEGERS (all of them?)
>>  
>>  
>>  
>> +.. opcode:: FSLT - Float Set On Less Than (ordered)
>> +
>> +.. math::
>> +
>> +  dst.x = (src0.x < src1.x) ? ~0 : 0
>> +
>> +  dst.y = (src0.y < src1.y) ? ~0 : 0
>> +
>> +  dst.z = (src0.z < src1.z) ? ~0 : 0
>> +
>> +  dst.w = (src0.w < src1.w) ? ~0 : 0
>> +
>> +
>>  .. opcode:: ISLT - Signed Integer Set On Less Than
>>  
>>  .. math::
>> @@ -1351,6 +1364,19 @@ Support for these opcodes indicated by PIPE_SHADER_CAP_INTEGERS (all of them?)
>>    dst.w = (src0.w < src1.w) ? ~0 : 0
>>  
>>  
>> +.. opcode:: FSGE - Float Set On Greater Equal Than (ordered)
>> +
>> +.. math::
>> +
>> +  dst.x = (src0.x >= src1.x) ? ~0 : 0
>> +
>> +  dst.y = (src0.y >= src1.y) ? ~0 : 0
>> +
>> +  dst.z = (src0.z >= src1.z) ? ~0 : 0
>> +
>> +  dst.w = (src0.w >= src1.w) ? ~0 : 0
>> +
>> +
>>  .. opcode:: ISGE - Signed Integer Set On Greater Equal Than
>>  
>>  .. math::
>> @@ -1377,6 +1403,19 @@ Support for these opcodes indicated by PIPE_SHADER_CAP_INTEGERS (all of them?)
>>    dst.w = (src0.w >= src1.w) ? ~0 : 0
>>  
>>  
>> +.. opcode:: FSEQ - Float Set On Equal (ordered)
>> +
>> +.. math::
>> +
>> +  dst.x = (src0.x == src1.x) ? ~0 : 0
>> +
>> +  dst.y = (src0.y == src1.y) ? ~0 : 0
>> +
>> +  dst.z = (src0.z == src1.z) ? ~0 : 0
>> +
>> +  dst.w = (src0.w == src1.w) ? ~0 : 0
>> +
>> +
>>  .. opcode:: USEQ - Integer Set On Equal
>>  
>>  .. math::
>> @@ -1390,6 +1429,19 @@ Support for these opcodes indicated by PIPE_SHADER_CAP_INTEGERS (all of them?)
>>    dst.w = (src0.w == src1.w) ? ~0 : 0
>>  
>>  
>> +.. opcode:: FSNE - Float Set On Not Equal (unordered)
>> +
>> +.. math::
>> +
>> +  dst.x = (src0.x != src1.x) ? ~0 : 0
>> +
>> +  dst.y = (src0.y != src1.y) ? ~0 : 0
>> +
>> +  dst.z = (src0.z != src1.z) ? ~0 : 0
>> +
>> +  dst.w = (src0.w != src1.w) ? ~0 : 0
>> +
>> +
>>  .. opcode:: USNE - Integer Set On Not Equal
>>  
>>  .. math::
>>
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