[Mesa-dev] [PATCH v2 1/4] nir: set default lod to texture opcodes that needed it but don't provide it

[Eric Anholt]

Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:

> [ Unknown signature status ]
> On Tuesday, October 10, 2017 11:53:27 AM CEST Eric Anholt wrote:
>> Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:
>> > Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
>> > ---
>> > 
>> >  src/compiler/nir/nir_lower_tex.c | 68
>> >  ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68
>> >  insertions(+)
>> > 
>> > diff --git a/src/compiler/nir/nir_lower_tex.c
>> > b/src/compiler/nir/nir_lower_tex.c index 65681decb1c..d3380710405 100644
>> > --- a/src/compiler/nir/nir_lower_tex.c
>> > +++ b/src/compiler/nir/nir_lower_tex.c
>> > @@ -717,6 +717,52 @@ linearize_srgb_result(nir_builder *b, nir_tex_instr
>> > *tex)> 
>> >                                    result->parent_instr);
>> >  
>> >  }
>> > 
>> > +static void
>> > +set_default_lod(nir_builder *b, nir_tex_instr *tex)
>> > +{
>> > +   b->cursor = nir_before_instr(&tex->instr);
>> > +
>> > +   /* We are going to emit the same texture but adding a default LOD.
>> > +    */
>> > +   int num_srcs = tex->num_srcs + 1;
>> > +   nir_tex_instr *new = nir_tex_instr_create(b->shader, num_srcs);
>> > +
>> > +   new->op = tex->op;
>> > +   new->sampler_dim = tex->sampler_dim;
>> > +   new->texture_index = tex->texture_index;
>> > +   new->dest_type = tex->dest_type;
>> > +   new->is_array = tex->is_array;
>> > +   new->is_shadow = tex->is_shadow;
>> > +   new->is_new_style_shadow = tex->is_new_style_shadow;
>> > +   new->sampler_index = tex->sampler_index;
>> > +   new->texture = nir_deref_var_clone(tex->texture, new);
>> > +   new->sampler = nir_deref_var_clone(tex->sampler, new);
>> > +   new->coord_components = tex->coord_components;
>> 
>> Couldn't we just make a new srcs array of num_srcs+1, memcpy the old
>> srcs/types over, add our new use of the immediate 0 lod to it by
>> manipulating the immediate's uses list
>
> This is an interesting approach.  I have done the following:
>
>    b->cursor = nir_before_instr(&tex->instr);
>
>    nir_tex_src *srcs = ralloc_array(tex, nir_tex_src, tex->num_srcs + 1);
>    memcpy(srcs, tex->src, sizeof(nir_tex_src) * tex->num_srcs);
>
>    srcs[tex->num_srcs + 1].src = nir_src_for_ssa(nir_imm_int(b, 0));
>    srcs[tex->num_srcs + 1].src_type = nir_tex_src_lod;
>    tex->num_srcs++;
>    ralloc_free(tex->src);
>    tex->src = srcs;
>
> However, it crashes when validating ssa def. I also tried calling 
> nir_ssa_def_rewrite_uses() but I am not sure how to do it for this case, 
> probably I am missing something.
>
> How can I manipulate the immediate's uses list for this case? Can you provide 
> an example?

When you nir_instr_insert() in your original code, add_defs_uses() will
call add_use_cb() on this src.  I was thinking that you could just
open-code that bit (or maybe we want to make the body of that function
public?)

Oh, wait, reallocating the srcs array would break the uses entries of
all the other srcs, so you'd need to remove uses from the old list and
add all of the new list.  It's less clear to me now whether this is a
good way to go.
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