[Mesa-dev] [PATCH] gallium/tgsi: clarify (possibly change) TGSI_OPCODE_UCMP definition

[Marek Olšák]

Modifiers are actually very useful with MOV. However I don't think the
modifiers really care what the type is. They just change the sign bit
of float (which is a bitwise operation). Also, UCMP doesn't do
anything with the 2nd and 3rd argument, so their types don't matter.

I think the ABS and SUB opcodes should be removed in favor of the modifiers.

Marek

On Wed, May 8, 2013 at 12:14 PM, Christoph Bumiller
<e0425955 at student.tuwien.ac.at> wrote:
> On 08.05.2013 03:48, sroland at vmware.com wrote:
>> From: Roland Scheidegger <sroland at vmware.com>
>>
>> UCMP while an integer opcode isn't really consistently implemented as
>> having all integer arguments. softpipe will assume all arguments are
>> ints, whereas gallivm has the arguments defined as untyped which
>> means they'll get treated as floats. This means input modifiers will
>> not work the same. Fix this by saying only first arg is an integer,
>> which seems more useful than making all arguments integers - this would
>> be similar to d3d10 movc opcode.
>> ---
>>  src/gallium/docs/source/tgsi.rst |    5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
>> index 3af1fb7..852f8a0 100644
>> --- a/src/gallium/docs/source/tgsi.rst
>> +++ b/src/gallium/docs/source/tgsi.rst
>> @@ -1291,6 +1291,11 @@ Support for these opcodes indicated by PIPE_SHADER_CAP_INTEGERS (all of them?)
>>
>>  .. opcode:: UCMP - Integer Conditional Move
>>
>> +.. note::
>> +
>> +   Only the first source arg is an integer, the 2nd and 3rd ones are
>> +   considered floats (for input modifier purposes).
>> +
>
> As long as you patch up all the occurrences of
> tgsi_opcode_infer_src_type and make it take an argument to identify the
> source ...
>
> I'd rather just forbid modifiers on moves, i.e. MOV and UCMP, since at
> least MOV returns TGSI_TYPE_UNTYPED and untyped values can't be operated on.
> For the ordinary MOV we have NEG and ABS, and for UCMP the backend
> optimizer can take care of merging modifiers into the instruction
> (nvc0's UCMP (slct u32) doesn't support modifiers).
>
>>  .. math::
>>
>>    dst.x = src0.x ? src1.x : src2.x
>>
>
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