[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:

> 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));

>           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.

> -            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.
> -- 
> 2.5.0
>
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