[Nouveau] [PATCH v2] nv50/ir: Handle OP_CVT when folding constant expressions

[Ilia Mirkin]

On Sun, Jan 11, 2015 at 12:27 PM, Tobias Klausmann
<tobias.johannes.klausmann at mni.thm.de> wrote:
>
>
> On 11.01.2015 01:58, Ilia Mirkin wrote:
>>
>> On Fri, Jan 9, 2015 at 8:24 PM, Tobias Klausmann
>> <tobias.johannes.klausmann at mni.thm.de> wrote:
>>>
>>> Folding for conversions: F32->(U{16/32}, S{16/32}) and (U{16/32},
>>> {S16/32})->F32
>>>
>>> Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann at mni.thm.de>
>>> ---
>>> V2: beat me, whip me, split out F64
>>>
>>>   .../drivers/nouveau/codegen/nv50_ir_peephole.cpp   | 81
>>> ++++++++++++++++++++++
>>>   1 file changed, 81 insertions(+)
>>>
>>> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
>>> b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
>>> index 9a0bb60..741c74f 100644
>>> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
>>> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
>>> @@ -997,6 +997,87 @@ ConstantFolding::opnd(Instruction *i, ImmediateValue
>>> &imm0, int s)
>>>         i->op = OP_MOV;
>>>         break;
>>>      }
>>> +   case OP_CVT: {
>>> +      Storage res;
>>> +      bld.setPosition(i, true); /* make sure bld is init'ed */
>>> +      switch(i->dType) {
>>> +      case TYPE_U16:
>>> +         switch (i->sType) {
>>> +         case TYPE_F32:
>>> +            if (i->saturate)
>>> +               res.data.u16 = util_iround(CLAMP(imm0.reg.data.f32, 0,
>>> +                                                UINT16_MAX));
>>
>> Where did this saturate stuff come from? It doesn't make sense to
>> saturate to a non-float dtype. I'd go ahead and just
>> assert(!i->saturate) in the int dtype cases.
>>
>> One does wonder what the hw does if the float doesn't fit in the
>> destination... whether it saturates or not. I don't hugely care
>> though.
>
> Actually i can't remember why that was added in the first place, i'll go
> ahead and follow your advice here.

Oh wait... this was to support saturating an array access into a u16...

         const int sat = (i->op == OP_TXF) ? 1 : 0;
         DataType sTy = (i->op == OP_TXF) ? TYPE_U32 : TYPE_F32;
         bld.mkCvt(OP_CVT, TYPE_U16, layer, sTy, src)->saturate = sat;

So... basically if the source is a U32 and the dest is a U16, we want
to saturate there? IMO this is such a minor use-case that it doesn't
really matter. However I guess you can keep the saturate bits around
if you like.

  -ilia