On Tue, Feb 27, 2018 at 5:27 AM, Jose Maria Casanova Crespo <
jmcasan...@igalia.com> wrote:
> 16-bit load_ubo/ssbo operations that call do_untyped_read_vector don't
> guarantee that offsets are multiple of 4-bytes as required by untyped_read
> message. This happens for example in the case of f16mat3x3 when then
> VK_KHR_relaxed_block_layout is enabled.
>
> Vectors reads when we have non-constant offsets are implemented with
> multiple byte_scattered_read messages that not require 32-bit aligned
> offsets.
>
> Now for all constant offsets we can use the untyped_read_surface message.
> In the case of constant offsets not aligned to 32-bits, we calculate a
> start offset 32-bit aligned and use the shuffle_32bit_load_result_to_
> 16bit_data
> function and the first_component parameter to skip the copy of the unneeded
> component.
>
> v2: Use untyped_read_surface messages always we have constant offsets.
> (Jason Ekstrand)
> ---
> src/intel/compiler/brw_fs_nir.cpp | 54 +++++++++++++++++++++++++++++-
> ---------
> 1 file changed, 40 insertions(+), 14 deletions(-)
>
> diff --git a/src/intel/compiler/brw_fs_nir.cpp
> b/src/intel/compiler/brw_fs_nir.cpp
> index 5567433a19e..affb242668a 100644
> --- a/src/intel/compiler/brw_fs_nir.cpp
> +++ b/src/intel/compiler/brw_fs_nir.cpp
> @@ -2304,28 +2304,54 @@ do_untyped_vector_read(const fs_builder &bld,
> {
> if (type_sz(dest.type) <= 2) {
> assert(dest.stride == 1);
> + boolean is_const_offset = offset_reg.file == BRW_IMMEDIATE_VALUE;
>
> - if (num_components > 1) {
> - /* Pairs of 16-bit components can be read with untyped read, for
> 16-bit
> - * vec3 4th component is ignored.
> + if (is_const_offset) {
> + uint32_t start = offset_reg.ud & ~3;
> + uint32_t end = offset_reg.ud + num_components *
> type_sz(dest.type);
> + end = ALIGN(end, 4);
> + assert (end - start <= 16);
> +
> + /* At this point we have 16-bit component/s that have constant
> + * offset aligned to 4-bytes that can be read with untyped_reads.
> + * untyped_read message requires 32-bit aligned offsets.
> */
> + unsigned first_component = (offset_reg.ud & 3) /
> type_sz(dest.type);
> + unsigned num_components_32bit =
> + DIV_ROUND_UP(first_component + num_components, 4 /
> type_sz(dest.type));
>
This could also be (end - start) / 4. You don't even need DIV_ROUND_UP
since both start and end are 4-aligned.
> +
> fs_reg read_result =
> - emit_untyped_read(bld, surf_index, offset_reg,
> - 1 /* dims */, DIV_ROUND_UP(num_components,
> 2),
> + emit_untyped_read(bld, surf_index, brw_imm_ud(start),
> + 1 /* dims */,
> + num_components_32bit,
> BRW_PREDICATE_NONE);
> shuffle_32bit_load_result_to_16bit_data(bld,
> retype(dest, BRW_REGISTER_TYPE_W),
> retype(read_result, BRW_REGISTER_TYPE_D),
> - num_components, 0);
> + num_components, first_component);
> } else {
> - assert(num_components == 1);
> - /* scalar 16-bit are read using one byte_scattered_read message
> */
> - fs_reg read_result =
> - emit_byte_scattered_read(bld, surf_index, offset_reg,
> - 1 /* dims */, 1,
> - type_sz(dest.type) * 8 /* bit_size
> */,
> - BRW_PREDICATE_NONE);
> - bld.MOV(dest, subscript(read_result, dest.type, 0));
> + fs_reg read_offset = bld.vgrf(BRW_REGISTER_TYPE_UD);
> + bld.MOV(read_offset, offset_reg);
> + unsigned first_component = 0;
> + unsigned pending_components = num_components;
> + while (pending_components > 0) {
>
Now that we're not doing anything crazy, this can be a simple for loop:
for (unsigned i = 0; i < num_components; i++) {
if (i == 0)
bld.MOV(read_offset, offset_reg);
else
bld.ADD(read_offset, offset_reg, brw_imm_ud(i * type_sz(dst.type)));
fs_reg read_result =
emit_byte_scattered_read(...);
bld.MOV(offset(dest, bld, i), subscript(read_result, dst.type, 0));
}
> + /* Non constant offsets are not guaranteed to be aligned
> 32-bits
> + * so they are read using one byte_scattered_read message
> + * for each component.
> + */
> + fs_reg read_result =
> + emit_byte_scattered_read(bld, surf_index, read_offset,
> + 1 /* dims */, 1,
> + type_sz(dest.type) * 8 /*
> bit_size */,
> + BRW_PREDICATE_NONE);
> + shuffle_32bit_load_result_to_16bit_data(bld,
> + retype(offset(dest, bld, first_component),
> BRW_REGISTER_TYPE_W),
> + retype(read_result, BRW_REGISTER_TYPE_D),
> + 1, 0);
> + pending_components--;
> + first_component ++;
> + bld.ADD(read_offset, offset_reg, brw_imm_ud(2 *
> first_component));
> + }
> }
> } else if (type_sz(dest.type) == 4) {
> fs_reg read_result = emit_untyped_read(bld, surf_index, offset_reg,
> --
> 2.14.3
>
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