[Mesa-dev] [PATCH 06/13] nir/lower_double_ops: lower floor()

[Samuel Iglesias Gonsálvez]

On 23/04/16 00:17, Jason Ekstrand wrote:
> On Fri, Apr 22, 2016 at 3:13 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> 
>>
>>
>> On Tue, Apr 12, 2016 at 1:05 AM, Samuel Iglesias Gonsálvez <
>> siglesias at igalia.com> wrote:
>>
>>> From: Iago Toral Quiroga <itoral at igalia.com>
>>>
>>> At least i965 hardware does not have native support for floor on doubles.
>>> ---
>>>  src/compiler/nir/nir.h                  |  1 +
>>>  src/compiler/nir/nir_lower_double_ops.c | 29
>>> +++++++++++++++++++++++++++++
>>>  2 files changed, 30 insertions(+)
>>>
>>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>>> index f83b2e0..b7231a7 100644
>>> --- a/src/compiler/nir/nir.h
>>> +++ b/src/compiler/nir/nir.h
>>> @@ -2287,6 +2287,7 @@ typedef enum {
>>>     nir_lower_dsqrt = (1 << 1),
>>>     nir_lower_drsq = (1 << 2),
>>>     nir_lower_dtrunc = (1 << 3),
>>> +   nir_lower_dfloor = (1 << 4),
>>>  } nir_lower_doubles_options;
>>>
>>>  void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options
>>> options);
>>> diff --git a/src/compiler/nir/nir_lower_double_ops.c
>>> b/src/compiler/nir/nir_lower_double_ops.c
>>> index 9eec858..e1ec6da 100644
>>> --- a/src/compiler/nir/nir_lower_double_ops.c
>>> +++ b/src/compiler/nir/nir_lower_double_ops.c
>>> @@ -377,6 +377,27 @@ lower_trunc(nir_builder *b, nir_ssa_def *src)
>>>     return nir_pack_double_2x32_split(b, new_src_lo, new_src_hi);
>>>  }
>>>
>>> +static nir_ssa_def *
>>> +lower_floor(nir_builder *b, nir_ssa_def *src)
>>> +{
>>> +   /*
>>> +    * For x >= 0, floor(x) = trunc(x)
>>> +    * For x < 0,
>>> +    *    - if x is integer, floor(x) = x
>>> +    *    - otherwise, floor(x) = trunc(x) - 1
>>> +    */
>>> +   nir_ssa_def *tr = nir_ftrunc(b, src);
>>> +   return nir_bcsel(b,
>>> +                    nir_fge(b, src, nir_imm_double(b, 0.0)),
>>> +                    tr,
>>> +                    nir_bcsel(b,
>>> +                              nir_fne(b,
>>> +                                      nir_fsub(b, src, tr),
>>> +                                      nir_imm_double(b, 0.0)),
>>>
>>
>> As an aside, you can just as easily check "x is integer" by "x ==
>> truc(x)".  That might be simpler.  Same goes for ceil().
>>
> 
> One more thought (Sorry for all the e-mails): It might be better to
> implement this as
> 
> floor(x) = (x >= 0 || x == trunc(x)) ? trunc(x) : trunc(x) - 1;
> 
> That way you only have one bcsel and fewer 64-bit values floating around.
> It *might* reduce register pressure (not sure if it actually will).
> --Jason
> 

Yeah, good idea. I will do this change for floor() and ceil() and check
if it reduces register pressure. Anyway, it saves one bcsel which is great.

Thanks!

Sam

> 
>> +                              nir_fsub(b, tr, nir_imm_double(b, 1.0)),
>>> +                              src));
>>> +}
>>> +
>>>  static void
>>>  lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options
>>> options)
>>>  {
>>> @@ -405,6 +426,11 @@ lower_doubles_instr(nir_alu_instr *instr,
>>> nir_lower_doubles_options options)
>>>           return;
>>>        break;
>>>
>>> +   case nir_op_ffloor:
>>> +      if (!(options & nir_lower_dfloor))
>>> +         return;
>>> +      break;
>>> +
>>>     default:
>>>        return;
>>>     }
>>> @@ -431,6 +457,9 @@ lower_doubles_instr(nir_alu_instr *instr,
>>> nir_lower_doubles_options options)
>>>     case nir_op_ftrunc:
>>>        result = lower_trunc(&bld, src);
>>>        break;
>>> +   case nir_op_ffloor:
>>> +      result = lower_floor(&bld, src);
>>> +      break;
>>>     default:
>>>        unreachable("unhandled opcode");
>>>     }
>>> --
>>> 2.5.0
>>>
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>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>>
>>
>>
>