Keith Whitwell pisze:
> On Fri, 2009-10-30 at 03:43 -0700, michal wrote:
>
>> gallium: Add a PREDICATE register file.
>>
>> There's already a shader token that allows composition of predicated
>> instructions (tgsi_instruction_ext_predicate). However, there is no way
>> one can write to thos predicate registers in the first place.
>> ---
>> src/gallium/include/pipe/p_shader_tokens.h | 1 +
>> 1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/gallium/include/pipe/p_shader_tokens.h
>> b/src/gallium/include/pipe/p_shader_tokens.h
>> index de338c4..6aa8b27 100644
>> --- a/src/gallium/include/pipe/p_shader_tokens.h
>> +++ b/src/gallium/include/pipe/p_shader_tokens.h
>> @@ -79,6 +79,7 @@ enum tgsi_file_type {
>> TGSI_FILE_ADDRESS =6,
>> TGSI_FILE_IMMEDIATE =7,
>> TGSI_FILE_LOOP =8,
>> + TGSI_FILE_PREDICATE =9,
>> TGSI_FILE_COUNT /**< how many TGSI_FILE_ types */
>> };
>>
>
> Michal,
>
> Is your expectation that all drivers become able to understand
> instructions with predicates? That seems unreasonable.
>
> What is the expected way of setting a predicate register? What
> functionality will use this?
>
>
For example:
DECL IN[0..1]
DECL OUT[0]
DECL PRED[0]
1: MOV OUT[0], IN[0]
2: SGT PRED[0], IN[0], IN[1]
3: (PRED[0]) MOV OUT[0], IN[1]
In (2) we set each component of PRED[0] to 1.0 if the corresponding
components of IN[0] are greater than IN[1], and to 0.0 otherwise.
In (3) we write IN[1] to only those components of OUT[0], for which the
respective components of PRED[0] are non-zero.
> It seems there are three ways to do conditional execution in TGSI
> currently -- predicates, condition codes and IF/THEN/ELSE instructions.
>
> I'd really prefer to have at most two, and in fact preferably just one.
> Can you take a look at the three alternatives and figure out if one can
> be amputated?
>
>
We could kill off the condition codes -- no driver uses that, and it's
easier for us to emulate them with predicates than the other way round.
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