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

[Jason Ekstrand]

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


> +                              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
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
>
>
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