[Mesa-dev] [PATCH 01/16] st/nine: Handle special LIT case

[Axel Davy]

Le 24/04/2015 23:04, Ilia Mirkin a écrit :
> On Fri, Apr 24, 2015 at 4:09 PM, Axel Davy <axel.davy at ens.fr> wrote:
>> Signed-off-by: Axel Davy <axel.davy at ens.fr>
>> ---
>>   src/gallium/state_trackers/nine/nine_shader.c | 19 ++++++++++++++++++-
>>   1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/gallium/state_trackers/nine/nine_shader.c b/src/gallium/state_trackers/nine/nine_shader.c
>> index 2ba625e..0fd3d37 100644
>> --- a/src/gallium/state_trackers/nine/nine_shader.c
>> +++ b/src/gallium/state_trackers/nine/nine_shader.c
>> @@ -2040,6 +2040,23 @@ DECL_SPECIAL(LOG)
>>       return D3D_OK;
>>   }
>>
>> +DECL_SPECIAL(LIT)
>> +{
>> +    struct ureg_program *ureg = tx->ureg;
>> +    struct ureg_dst tmp = tx_scratch(tx);
>> +    struct ureg_dst dst = tx_dst_param(tx, &tx->insn.dst[0]);
>> +    struct ureg_src src = tx_src_param(tx, &tx->insn.src[0]);
>> +    ureg_LIT(ureg, tmp, src);
>> +    /* d3d9 LIT is the same than gallium LIT. One difference is that d3d9
>> +     * states that dst.z is 0 when src.y <= 0. Gallium definition can assign
>> +     * it 0^0 if src.w=0, which value is driver dependent. */
>> +    ureg_CMP(ureg, ureg_writemask(dst, TGSI_WRITEMASK_Z),
>> +             ureg_negate(ureg_scalar(src, TGSI_SWIZZLE_Y)),
>> +             ureg_src(tmp), ureg_imm1f(ureg, 0.0f));
>> +    ureg_MOV(ureg, ureg_writemask(dst, TGSI_WRITEMASK_XYW), ureg_src(tmp));
> Why use a separate temp? Couldn't you just
>
> ureg_LIT(ureg, dst, src);
> ureg_CMP(ureg, writemask(dst, Z), -src.y, ureg_src(dst), ureg_imm1f(0.0)) ?
>
Isn't there a restriction in the case dst is an output register of the 
shader ? Reading from it would be forbidden.
Also likely it is easier to optimiser for compilers with the temp version.