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

[Francisco Jerez]

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

> On Wed, 2016-05-11 at 17:12 +0200, Samuel Iglesias Gonsálvez wrote:
>> 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);
>> 
>
> Looking at patch 13, offset(dest, bld, i) needs to be adjusted to save
> the remaining components, so I think the MOV is clearer as it is now
> than the proposed change.
>
I won't pretend I understand everything going on in PATCH 13 :P, but
feel free to keep the induction on the destination register if it turns
out to be convenient later on.

> Sam
>
>> 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.
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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