On Mon, 2015-10-19 at 23:11 -0700, Matt Turner wrote:
> On Mon, Oct 19, 2015 at 9:09 PM, Matt Turner <matts...@gmail.com> wrote:
> > We implement textureQueryLevels (which takes no arguments, save the
> > sampler) using the resinfo message (which takes an argument of LOD).
> > Without initializing it, we'd generate a MOV from the null register to
> > load the LOD argument.
> > ---
> > src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
> > b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
> > index ea1e3e7..c942c80 100644
> > --- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
> > @@ -1579,7 +1579,7 @@ vec4_visitor::nir_emit_texture(nir_tex_instr *instr)
> > const glsl_type *coord_type = NULL;
> > src_reg shadow_comparitor;
> > src_reg offset_value;
> > - src_reg lod, lod2;
> > + src_reg lod(0.0f), lod2;
> > src_reg sample_index;
> > src_reg mcs;
>
> The fs backend handles this differently --
>
> if (op == ir_query_levels) {
> /* textureQueryLevels() is implemented in terms of TXS so we need to
> * pass a valid LOD argument.
> */
> assert(lod.file == BAD_FILE);
> lod = fs_reg(0u);
> }
>
> That kinda seems worse -- but it does indicate that I should probably
> initialize lod with 0u instead, though it doesn't seem to matter...
I don't care much either way, the good thing about the code in the fs
backend is that it makes things more explicit. I think I kind of like
that a bit better but works for me either way. Whatever we do, we should
probably use the same solution in both backends though.
> mov(8) g10<1>F [0F, 0F, 0F, 0F]VF
> send(8) g3<1>UW g10<8,8,1>F
> sampler resinfo SIMD8 Surface = 1 Sampler = 0 mlen 1 rlen 4
>
> Opinions?
isn't LOD a float value by definition? Also, there are other parts of
the FS code that initialize it to 0.0, like this (from
lower_sampler_logical_send_gen7):
if (bld.shader->stage != MESA_SHADER_FRAGMENT &&
op == SHADER_OPCODE_TEX) {
op = SHADER_OPCODE_TXL;
lod = fs_reg(0.0f);
}
In any case, in that same function we do:
for (unsigned i = 0; i < ARRAY_SIZE(sources); i++)
sources[i] = bld.vgrf(BRW_REGISTER_TYPE_F);
and then later we do:
bld.MOV(sources[length], lod)
so even if we initialize lod to 0u it is going to end up as a float,
which explains the result you obtained, so I think float is probably
what we want.
Iago
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