[Mesa-dev] [PATCH v3 024/104] nir: Support deref instructions in lower_system_values

[Jason Ekstrand]

On Fri, Apr 6, 2018 at 10:37 PM, Jason Ekstrand <jason at jlekstrand.net>
wrote:

> On Fri, Apr 6, 2018 at 2:47 PM, Caio Marcelo de Oliveira Filho <
> caio.oliveira at intel.com> wrote:
>
>> On Tue, Apr 03, 2018 at 11:32:51AM -0700, Jason Ekstrand wrote:
>> > ---
>> >  src/compiler/nir/nir_lower_system_values.c | 13 ++++++++++---
>> >  1 file changed, 10 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/src/compiler/nir/nir_lower_system_values.c
>> b/src/compiler/nir/nir_lower_system_values.c
>> > index fb560ee..104df51 100644
>> > --- a/src/compiler/nir/nir_lower_system_values.c
>> > +++ b/src/compiler/nir/nir_lower_system_values.c
>> > @@ -39,10 +39,15 @@ convert_block(nir_block *block, nir_builder *b)
>> >
>> >        nir_intrinsic_instr *load_var = nir_instr_as_intrinsic(instr);
>> >
>> > -      if (load_var->intrinsic != nir_intrinsic_load_var)
>> > -         continue;
>> > +      nir_variable *var;
>> > +      if (load_var->intrinsic == nir_intrinsic_load_var) {
>> > +         var = load_var->variables[0]->var;
>> > +      } else if (load_var->intrinsic == nir_intrinsic_load_deref) {
>> > +         var = nir_deref_instr_get_variable(n
>> ir_src_as_deref(load_var->src[0]));
>>
>> Question: nir_deref_instr_get_variable will walk the deref instr
>> chain, but does it even make sense if there's a array or struct in
>> this deref chain? Should this be asserted?
>>
>
> That's an interesting question.  Certainly, at this point in the patch
> series, we can't make that assumption.  This is because we haven't checked
> the mode yet.  However, once we can assume deref instructions, we can check
> the mode and then go on to find the var.  Maybe something like this
> (untested):
>
> https://gitlab.freedesktop.org/jekstrand/mesa/commit/
> 33aee39955eff842d6ea263da2f36e60287e62ee
>

It turns out that there is one system value which is an array:
gl_SampleMask.  However, due to details, we only ever load element 0 so we
can ignore the array deref in that case.  Unfortunately, this means that we
can't do any better than what we have here. :-(
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