[Mesa-dev] [PATCH 12/23] i965/fs: fix pull constant load component selection for doubles

[Samuel Iglesias Gonsálvez]

On Tue, 2016-05-10 at 21:06 -0700, Francisco Jerez wrote:
> Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:
> 
> > 
> > From: Iago Toral Quiroga <itoral at igalia.com>
> > 
> > UNIFORM_PULL_CONSTANT_LOAD is used to load a contiguous vec4
> > starting at a
> > constant offset that is 16-byte aligned. If we need to access an
> > unaligned
> > offset we emit a load with an aligned offset and use the remaining
> > constant
> > offset to select the component into the vec4 result that we are
> > interested
> > in. This component must be computed in units of the type size,
> > since that
> > is what fs_reg::set_smear expects.
> > 
> > This patch does this change in the two places where we use this
> > message:
> > In demote_pull_constants when we lower uniform access with constant
> > offset
> > into the pull constant buffer and in UBO loads with constant
> > offset.
> > ---
> >  src/mesa/drivers/dri/i965/brw_fs.cpp     | 3 ++-
> >  src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 4 +++-
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > index 0e69be8..dff13ea 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > @@ -2268,7 +2268,8 @@ fs_visitor::lower_constant_loads()
> >           inst->src[i].file = VGRF;
> >           inst->src[i].nr = dst.nr;
> >           inst->src[i].reg_offset = 0;
> > -         inst->src[i].set_smear(pull_index & 3);
> > +         unsigned type_slots = MAX2(1, type_sz(inst->dst.type) /
> > 4);
> > +         inst->src[i].set_smear((pull_index & 3) / type_slots);
> >  
> This cannot be right, why should we care what the destination type of
> the instruction is while lowering a uniform source?  Also I don't
> think
> the MAX2 call is correct because *if* type_sz(inst->dst.type) / 4 < 1
> you'll force type_slots to 1 and end up interpreting the pull_index
> in
> the wrong units.  How about:
> 
> > 
> >           inst->src[i].set_smear((pull_index & 3) * 4 /
> >                                  type_sz(inst->src[i].type));
> > 

OK

> >           brw_mark_surface_used(prog_data, index);
> >        }
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > index 4cd219a..532ca65 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
> > @@ -2980,8 +2980,10 @@ fs_visitor::nir_emit_intrinsic(const
> > fs_builder &bld, nir_intrinsic_instr *instr
> >           bld.emit(FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD,
> > packed_consts,
> >                    surf_index, const_offset_reg);
> >  
> > +         unsigned component_base =
> > +            (const_offset->u32[0] % 16) / MAX2(1,
> > type_sz(dest.type));
> Rather than dividing by the type size only to let set_smear multiply
> by
> the type size again, I think it would be cleaner to do something
> like:
> 
> > 
> >           const fs_reg consts = byte_offset(packed_consts,
> > const_offset->u32[0] % 16);
> > 
> >           for (unsigned i = 0; i < instr->num_components; i++) {
> then here:
> 
> > 
> >              bld.MOV(offset(dest, bld, i), component(consts, i));
> and then remove the rest of the loop.
> 

I am having troubles with adapting patch 13/23 to this way because the
following assert in component() is failing for some tests:
    
    assert(reg.subreg_offset == 0);

consts.subreg is not zero thanks to byte_offset() call.

So I prefer to go to a mixed solution: keep set_smear() usage, then:

   bld.MOV(offset(dest, bld, i), packed_consts);

and remove the rest of the loop.

Sam

> > 
> > -            packed_consts.set_smear(const_offset->u32[0] % 16 / 4
> > + i);
> > +            packed_consts.set_smear(component_base + i);
> >  
> >              /* The std140 packing rules don't allow vectors to
> > cross 16-byte
> >               * boundaries, and a reg is 32 bytes.