From: Jason Ekstrand Date: Wed, 6 Nov 2019 18:09:56 +0000 (-0600) Subject: nir/builder: Add a nir_extract_bits helper X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=d0bbf98c968179c4d23c88d1d1748e45afead78f;p=mesa.git nir/builder: Add a nir_extract_bits helper This new helper is better than nir_bitcast_vector because it's able to take a (mostly) arbitrary range from the source vector. The only requirement is that first_bit has to be aligned to the smaller of the two bit sizes. It wouldn't be hard to lift that requirement but it's reasonable for now. Reviewed-by: Caio Marcelo de Oliveira Filho --- diff --git a/src/compiler/nir/nir_builder.h b/src/compiler/nir/nir_builder.h index 5714ea08ed2..de00fe7e389 100644 --- a/src/compiler/nir/nir_builder.h +++ b/src/compiler/nir/nir_builder.h @@ -757,6 +757,85 @@ nir_unpack_bits(nir_builder *b, nir_ssa_def *src, unsigned dest_bit_size) return nir_vec(b, dest_comps, dest_num_components); } +/** + * Treats srcs as if it's one big blob of bits and extracts the range of bits + * given by + * + * [first_bit, first_bit + dest_num_components * dest_bit_size) + * + * The range can have any alignment or size as long as it's an integer number + * of destination components and fits inside the concatenated sources. + * + * TODO: The one caveat here is that we can't handle byte alignment if 64-bit + * values are involved because that would require pack/unpack to/from a vec8 + * which NIR currently does not support. + */ +static inline nir_ssa_def * +nir_extract_bits(nir_builder *b, nir_ssa_def **srcs, unsigned num_srcs, + unsigned first_bit, + unsigned dest_num_components, unsigned dest_bit_size) +{ + const unsigned num_bits = dest_num_components * dest_bit_size; + + /* Figure out the common bit size */ + unsigned common_bit_size = dest_bit_size; + for (unsigned i = 0; i < num_srcs; i++) + common_bit_size = MIN2(common_bit_size, srcs[i]->bit_size); + if (first_bit > 0) + common_bit_size = MIN2(common_bit_size, (1 << (ffs(first_bit) - 1))); + + /* We don't want to have to deal with 1-bit values */ + assert(common_bit_size >= 8); + + nir_ssa_def *common_comps[NIR_MAX_VEC_COMPONENTS * sizeof(uint64_t)]; + assert(num_bits / common_bit_size <= ARRAY_SIZE(common_comps)); + + /* First, unpack to the common bit size and select the components from the + * source. + */ + int src_idx = -1; + unsigned src_start_bit = 0; + unsigned src_end_bit = 0; + for (unsigned i = 0; i < num_bits / common_bit_size; i++) { + const unsigned bit = first_bit + (i * common_bit_size); + while (bit >= src_end_bit) { + src_idx++; + assert(src_idx < num_srcs); + src_start_bit = src_end_bit; + src_end_bit += srcs[src_idx]->bit_size * + srcs[src_idx]->num_components; + } + assert(bit >= src_start_bit); + assert(bit + common_bit_size <= src_end_bit); + const unsigned rel_bit = bit - src_start_bit; + const unsigned src_bit_size = srcs[src_idx]->bit_size; + + nir_ssa_def *comp = nir_channel(b, srcs[src_idx], + rel_bit / src_bit_size); + if (srcs[src_idx]->bit_size > common_bit_size) { + nir_ssa_def *unpacked = nir_unpack_bits(b, comp, common_bit_size); + comp = nir_channel(b, unpacked, (rel_bit % src_bit_size) / + common_bit_size); + } + common_comps[i] = comp; + } + + /* Now, re-pack the destination if we have to */ + if (dest_bit_size > common_bit_size) { + unsigned common_per_dest = dest_bit_size / common_bit_size; + nir_ssa_def *dest_comps[NIR_MAX_VEC_COMPONENTS]; + for (unsigned i = 0; i < dest_num_components; i++) { + nir_ssa_def *unpacked = nir_vec(b, common_comps + i * common_per_dest, + common_per_dest); + dest_comps[i] = nir_pack_bits(b, unpacked, dest_bit_size); + } + return nir_vec(b, dest_comps, dest_num_components); + } else { + assert(dest_bit_size == common_bit_size); + return nir_vec(b, common_comps, dest_num_components); + } +} + static inline nir_ssa_def * nir_bitcast_vector(nir_builder *b, nir_ssa_def *src, unsigned dest_bit_size) { @@ -765,43 +844,7 @@ nir_bitcast_vector(nir_builder *b, nir_ssa_def *src, unsigned dest_bit_size) (src->bit_size * src->num_components) / dest_bit_size; assert(dest_num_components <= NIR_MAX_VEC_COMPONENTS); - if (src->bit_size > dest_bit_size) { - assert(src->bit_size % dest_bit_size == 0); - if (src->num_components == 1) { - return nir_unpack_bits(b, src, dest_bit_size); - } else { - const unsigned divisor = src->bit_size / dest_bit_size; - assert(src->num_components * divisor == dest_num_components); - nir_ssa_def *dest[NIR_MAX_VEC_COMPONENTS]; - for (unsigned i = 0; i < src->num_components; i++) { - nir_ssa_def *unpacked = - nir_unpack_bits(b, nir_channel(b, src, i), dest_bit_size); - assert(unpacked->num_components == divisor); - for (unsigned j = 0; j < divisor; j++) - dest[i * divisor + j] = nir_channel(b, unpacked, j); - } - return nir_vec(b, dest, dest_num_components); - } - } else if (src->bit_size < dest_bit_size) { - assert(dest_bit_size % src->bit_size == 0); - if (dest_num_components == 1) { - return nir_pack_bits(b, src, dest_bit_size); - } else { - const unsigned divisor = dest_bit_size / src->bit_size; - assert(src->num_components == dest_num_components * divisor); - nir_ssa_def *dest[NIR_MAX_VEC_COMPONENTS]; - for (unsigned i = 0; i < dest_num_components; i++) { - nir_component_mask_t src_mask = - ((1 << divisor) - 1) << (i * divisor); - dest[i] = nir_pack_bits(b, nir_channels(b, src, src_mask), - dest_bit_size); - } - return nir_vec(b, dest, dest_num_components); - } - } else { - assert(src->bit_size == dest_bit_size); - return src; - } + return nir_extract_bits(b, &src, 1, 0, dest_num_components, dest_bit_size); } /**