[Mesa-dev] [PATCH 8/9] i965/vec4: Handle saturated constants in opt_vector_float

[Matt Turner]

On Thu, Mar 17, 2016 at 11:52 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>
>
> On Thu, Mar 17, 2016 at 11:18 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>
>> On Thu, Mar 17, 2016 at 10:21 AM, Jason Ekstrand <jason at jlekstrand.net>
>> wrote:
>> > ---
>> >  src/mesa/drivers/dri/i965/brw_vec4.cpp | 8 +++++++-
>> >  1 file changed, 7 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> > b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> > index 155a550..02a00b3 100644
>> > --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> > +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> > @@ -384,7 +384,13 @@ vec4_visitor::opt_vector_float()
>> >           continue;
>> >        }
>> >
>> > -      int vf = brw_float_to_vf(inst->src[0].f);
>> > +      float f = inst->src[0].f;
>> > +      if (inst->saturate) {
>> > +         assert(inst->dst.type == BRW_REGISTER_TYPE_F);
>> > +         f = CLAMP(f, 0.0f, 1.0f);
>> > +      }
>> > +
>> > +      int vf = brw_float_to_vf(f);
>> >        if (vf == -1)
>> >           continue;
>>
>> Presumably the previous patch is to allow this to happen without
>> thinking about types.
>>
>> This does look like a legitimate bug fix, but what does this fix or
>> enable?
>
>
> Patch 9 removes the mov.sat optimization from opt_algebraic which was fixing
> up saturated constants before opt_vector_float ever saw them.  When I
> removed it, I got a bunch of piglit fails from things that were writing
> out-of-bounds constant values to auto-clampped outputs.  The problem was
> that opt_vector_float was just throwing the .sat away.

Oh, so this isn't even a legitimate bug fix unless you remove the code
this relies on...

Just keep the saturating code in opt_algebraic. Why would we remove it...?