[Mesa-dev] [PATCH 09/12] nir: Add lowering support for packing opcodes.

[Iago Toral]

On Thu, 2016-01-28 at 09:21 -0800, Matt Turner wrote:
> On Thu, Jan 28, 2016 at 12:32 AM, Iago Toral <itoral at igalia.com> wrote:
> > On Mon, 2016-01-25 at 15:18 -0800, Matt Turner wrote:
(...)
> >> diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
> >> index b761b54..56b0f5e 100644
> >> --- a/src/glsl/nir/nir_opt_algebraic.py
> >> +++ b/src/glsl/nir/nir_opt_algebraic.py
> >> @@ -258,6 +258,26 @@ optimizations = [
> >>     (('extract_uword', a, b),
> >>      ('iand', ('ushr', a, ('imul', b, 16)), 0xffff),
> >>      'options->lower_extract_word'),
> >> +
> >> +    (('pack_unorm_2x16', 'v'),
> >> +     ('pack_uvec2_to_uint',
> >> +        ('f2u', ('fround_even', ('fmul', ('fsat', 'v'), 65535.0)))),
> >> +     'options->lower_pack_unorm_2x16'),
> >> +
> >> +    (('pack_unorm_4x8', 'v'),
> >> +     ('pack_uvec4_to_uint',
> >> +        ('f2u', ('fround_even', ('fmul', ('fsat', 'v'), 255.0)))),
> >> +     'options->lower_pack_unorm_4x8'),
> >> +
> >> +    (('pack_snorm_2x16', 'v'),
> >> +     ('pack_uvec2_to_uint',
> >> +        ('f2i', ('fround_even', ('fmul', ('fmin', 1.0, ('fmax', -1.0, 'v')), 32767.0)))),
> >> +     'options->lower_pack_snorm_2x16'),
> >> +
> >> +    (('pack_snorm_4x8', 'v'),
> >> +     ('pack_uvec4_to_uint',
> >> +        ('f2i', ('fround_even', ('fmul', ('fmin', 1.0, ('fmax', -1.0, 'v')), 127.0)))),
> >> +     'options->lower_pack_snorm_4x8'),
> >
> > I think the pack_snorm_* opcodes need a i2u conversion at the end.
> > That's what the GLSL IR lowering is doing and also what the spec [1]
> > seems to indicate:
> 
> Right, but since NIR operands are typeless, there's nothing to do (NIR
> doesn't even have i2u/u2i).

I suppose that since these pack the incoming vector components into an
uint it does not really matter in the end, since that won't affect the
bits involved. Anyway, why not use f2u instead of f2i, seems like that
would represent the semantics expected more accurately.

Iago