[Mesa-dev] [PATCH 2/2] nir: Add support for 8 and 16-bit types

[Jason Ekstrand]

Sorry I haven't gotten back on this.  It got lost somehow.

On Fri, Mar 10, 2017 at 1:56 AM, Iago Toral <itoral at igalia.com> wrote:

> On Thu, 2017-03-09 at 14:05 -0800, Jason Ekstrand wrote:
> > ---
> >  src/compiler/nir/nir.h                       |  4 ++++
> >  src/compiler/nir/nir_constant_expressions.py | 16 +++++++++++++++-
> >  src/compiler/nir/nir_opcodes.py              |  6 +++++-
> >  3 files changed, 24 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> > index 57b8be3..eaa103d 100644
> > --- a/src/compiler/nir/nir.h
> > +++ b/src/compiler/nir/nir.h
> > @@ -105,6 +105,10 @@ typedef enum {
> >  typedef union {
> >     float f32[4];
> >     double f64[4];
> > +   int8_t i8[4];
> > +   uint8_t u8[4];
> > +   int16_t i16[4];
> > +   uint16_t u16[4];
> >     int32_t i32[4];
> >     uint32_t u32[4];
> >     int64_t i64[4];
> >
> > diff --git a/src/compiler/nir/nir_constant_expressions.py
> > b/src/compiler/nir/nir_constant_expressions.py
> > index aecca8b..cbda4b1 100644
> > --- a/src/compiler/nir/nir_constant_expressions.py
> > +++ b/src/compiler/nir/nir_constant_expressions.py
> > @@ -14,8 +14,10 @@ def type_size(type_):
> >  def type_sizes(type_):
> >      if type_has_size(type_):
> >          return [type_size(type_)]
> > +    elif type_ == 'float':
> > +        return [16, 32, 64]
> >      else:
> > -        return [32, 64]
> > +        return [8, 16, 32, 64]
> >
> >  def type_add_size(type_, size):
> >      if type_has_size(type_):
> > @@ -34,6 +36,8 @@ def op_bit_sizes(op):
> >  def get_const_field(type_):
> >      if type_ == "bool32":
> >          return "u32"
> > +    elif type_ == "float16":
> > +        return "u16"
>
> I was wondering why not have a f16 field with type float16_t
> in nir_const_value instead,  but reading the rest of the patch it seems
> we really want to work with 32-bit floats and then encode results back to
> 16-bit values? Is it because there are some operations that we can't
> implement directly with half-floats?
>

Yes.  CPUs cannot, in general, work with 16-bit floats so there is no
actual float16_t type in C.  We typedef float to float16_t below just
because it makes the codegen easier.  In reality, all 16-bit operations
have to be done in 32-bit with a manual conversion to/from 16-bit float on
both sides.


> Iago
>
> >      else:
> >          m = type_split_re.match(type_)
> >          if not m:
> > @@ -246,6 +250,7 @@ unpack_half_1x16(uint16_t u)
> >  }
> >
> >  /* Some typed vector structures to make things like src0.y work */
> > +typedef float float16_t;
> >  typedef float float32_t;
> >  typedef double float64_t;
> >  typedef bool bool32_t;
> > @@ -297,6 +302,8 @@ evaluate_${name}(MAYBE_UNUSED unsigned
> > num_components, unsigned bit_size,
> >           % for k in range(op.input_sizes[j]):
> >              % if input_types[j] == "bool32":
> >                 _src[${j}].u32[${k}] != 0,
> > +            % elif input_types[j] == "float16":
> > +               _mesa_half_to_float(_src[${j}].u16[${k}]),
> >              % else:
> >                 _src[${j}].${get_const_field(input_types[j])}[${k}],
> >              % endif
> > @@ -322,6 +329,9 @@ evaluate_${name}(MAYBE_UNUSED unsigned
> > num_components, unsigned bit_size,
> >                    <% continue %>
> >                 % elif input_types[j] == "bool32":
> >                    const bool src${j} = _src[${j}].u32[_i] != 0;
> > +               % elif input_types[j] == "float16":
> > +                  const float src${j} =
> > +                     _mesa_half_to_float(_src[${j}].u16[_i]);
> >                 % else:
> >                    const ${input_types[j]}_t src${j} =
> >                       _src[${j}].${get_const_field(input_types[j])}[_
> > i];
> > @@ -344,6 +354,8 @@ evaluate_${name}(MAYBE_UNUSED unsigned
> > num_components, unsigned bit_size,
> >              % if output_type == "bool32":
> >                 ## Sanitize the C value to a proper NIR bool
> >                 _dst_val.u32[_i] = dst ? NIR_TRUE : NIR_FALSE;
> > +            % elif output_type == "float16":
> > +               _dst_val.u16[_i] = _mesa_float_to_half(dst);
> >              % else:
> >                 _dst_val.${get_const_field(output_type)}[_i] = dst;
> >              % endif
> > @@ -371,6 +383,8 @@ evaluate_${name}(MAYBE_UNUSED unsigned
> > num_components, unsigned bit_size,
> >              % if output_type == "bool32":
> >                 ## Sanitize the C value to a proper NIR bool
> >                 _dst_val.u32[${k}] = dst.${"xyzw"[k]} ? NIR_TRUE :
> > NIR_FALSE;
> > +            % elif output_type == "float16":
> > +               _dst_val.u16[${k}] =
> > _mesa_float_to_half(dst.${"xyzw"[k]});
> >              % else:
> >                 _dst_val.${get_const_field(output_type)}[${k}] =
> > dst.${"xyzw"[k]};
> >              % endif
> > diff --git a/src/compiler/nir/nir_opcodes.py
> > b/src/compiler/nir/nir_opcodes.py
> > index 53e9aff..37c655b 100644
> > --- a/src/compiler/nir/nir_opcodes.py
> > +++ b/src/compiler/nir/nir_opcodes.py
> > @@ -175,7 +175,11 @@ for src_t in [tint, tuint, tfloat]:
> >        dst_types = [tint, tuint, tfloat]
> >
> >     for dst_t in dst_types:
> > -      for bit_size in [32, 64]:
> > +      if dst_t == tfloat:
> > +         bit_sizes = [16, 32, 64]
> > +      else:
> > +         bit_sizes = [8, 16, 32, 64]
> > +      for bit_size in bit_sizes:
> >           unop_convert("{}2{}{}".format(src_t[0], dst_t[0],
> > bit_size),
> >                        dst_t + str(bit_size), src_t, "src0")
> >
>
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