/* * Copyright © 2015 Intel Corporation * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice (including the next * paragraph) shall be included in all copies or substantial portions of the * Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS * IN THE SOFTWARE. */ #include "brw_nir.h" #include "compiler/nir/nir.h" #include "util/u_dynarray.h" /** * \file brw_nir_analyze_ubo_ranges.c * * This pass decides which portions of UBOs to upload as push constants, * so shaders can access them as part of the thread payload, rather than * having to issue expensive memory reads to pull the data. * * The 3DSTATE_CONSTANT_* mechanism can push data from up to 4 different * buffers, in GRF (256-bit/32-byte) units. * * To do this, we examine NIR load_ubo intrinsics, recording the number of * loads at each offset. We track offsets at a 32-byte granularity, so even * fields with a bit of padding between them tend to fall into contiguous * ranges. We build a list of these ranges, tracking their "cost" (number * of registers required) and "benefit" (number of pull loads eliminated * by pushing the range). We then sort the list to obtain the four best * ranges (most benefit for the least cost). */ struct ubo_range_entry { struct brw_ubo_range range; int benefit; }; static int score(const struct ubo_range_entry *entry) { return 2 * entry->benefit - entry->range.length; } /** * Compares score for two UBO range entries. * * For a descending qsort(). */ static int cmp_ubo_range_entry(const void *va, const void *vb) { const struct ubo_range_entry *a = va; const struct ubo_range_entry *b = vb; /* Rank based on scores */ int delta = score(b) - score(a); /* Then use the UBO block index as a tie-breaker */ if (delta == 0) delta = b->range.block - a->range.block; /* Finally use the UBO offset as a second tie-breaker */ if (delta == 0) delta = b->range.block - a->range.block; return delta; } struct ubo_block_info { /* Each bit in the offsets bitfield represents a 32-byte section of data. * If it's set to one, there is interesting UBO data at that offset. If * not, there's a "hole" - padding between data - or just nothing at all. */ uint64_t offsets; uint8_t uses[64]; }; struct ubo_analysis_state { struct hash_table *blocks; bool uses_regular_uniforms; }; static struct ubo_block_info * get_block_info(struct ubo_analysis_state *state, int block) { uint32_t hash = block + 1; void *key = (void *) (uintptr_t) hash; struct hash_entry *entry = _mesa_hash_table_search_pre_hashed(state->blocks, hash, key); if (entry) return (struct ubo_block_info *) entry->data; struct ubo_block_info *info = rzalloc(state->blocks, struct ubo_block_info); _mesa_hash_table_insert_pre_hashed(state->blocks, hash, key, info); return info; } static void analyze_ubos_block(struct ubo_analysis_state *state, nir_block *block) { nir_foreach_instr(instr, block) { if (instr->type != nir_instr_type_intrinsic) continue; nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); switch (intrin->intrinsic) { case nir_intrinsic_load_uniform: case nir_intrinsic_image_deref_load: case nir_intrinsic_image_deref_store: case nir_intrinsic_image_deref_atomic_add: case nir_intrinsic_image_deref_atomic_min: case nir_intrinsic_image_deref_atomic_max: case nir_intrinsic_image_deref_atomic_and: case nir_intrinsic_image_deref_atomic_or: case nir_intrinsic_image_deref_atomic_xor: case nir_intrinsic_image_deref_atomic_exchange: case nir_intrinsic_image_deref_atomic_comp_swap: case nir_intrinsic_image_deref_size: state->uses_regular_uniforms = true; continue; case nir_intrinsic_load_ubo: break; /* Fall through to the analysis below */ default: continue; /* Not a uniform or UBO intrinsic */ } nir_const_value *block_const = nir_src_as_const_value(intrin->src[0]); nir_const_value *offset_const = nir_src_as_const_value(intrin->src[1]); if (block_const && offset_const) { const int block = block_const->u32[0]; const int offset = offset_const->u32[0] / 32; /* Avoid shifting by larger than the width of our bitfield, as this * is undefined in C. Even if we require multiple bits to represent * the entire value, it's OK to record a partial value - the backend * is capable of falling back to pull loads for later components of * vectors, as it has to shrink ranges for other reasons anyway. */ if (offset >= 64) continue; /* The value might span multiple 32-byte chunks. */ const int bytes = nir_intrinsic_dest_components(intrin) * (nir_dest_bit_size(intrin->dest) / 8); const int start = ROUND_DOWN_TO(offset_const->u32[0], 32); const int end = ALIGN(offset_const->u32[0] + bytes, 32); const int chunks = (end - start) / 32; /* TODO: should we count uses in loops as higher benefit? */ struct ubo_block_info *info = get_block_info(state, block); info->offsets |= ((1ull << chunks) - 1) << offset; info->uses[offset]++; } } } static void print_ubo_entry(FILE *file, const struct ubo_range_entry *entry, struct ubo_analysis_state *state) { struct ubo_block_info *info = get_block_info(state, entry->range.block); fprintf(file, "block %2d, start %2d, length %2d, bits = %"PRIx64", " "benefit %2d, cost %2d, score = %2d\n", entry->range.block, entry->range.start, entry->range.length, info->offsets, entry->benefit, entry->range.length, score(entry)); } void brw_nir_analyze_ubo_ranges(const struct brw_compiler *compiler, nir_shader *nir, const struct brw_vs_prog_key *vs_key, struct brw_ubo_range out_ranges[4]) { const struct gen_device_info *devinfo = compiler->devinfo; if ((devinfo->gen <= 7 && !devinfo->is_haswell) || !compiler->scalar_stage[nir->info.stage]) { memset(out_ranges, 0, 4 * sizeof(struct brw_ubo_range)); return; } void *mem_ctx = ralloc_context(NULL); struct ubo_analysis_state state = { .uses_regular_uniforms = false, .blocks = _mesa_hash_table_create(mem_ctx, NULL, _mesa_key_pointer_equal), }; switch (nir->info.stage) { case MESA_SHADER_VERTEX: if (vs_key && vs_key->nr_userclip_plane_consts > 0) state.uses_regular_uniforms = true; break; case MESA_SHADER_COMPUTE: /* Compute shaders use push constants to get the subgroup ID so it's * best to just assume some system values are pushed. */ state.uses_regular_uniforms = true; break; default: break; } /* Walk the IR, recording how many times each UBO block/offset is used. */ nir_foreach_function(function, nir) { if (function->impl) { nir_foreach_block(block, function->impl) { analyze_ubos_block(&state, block); } } } /* Find ranges: a block, starting 32-byte offset, and length. */ struct util_dynarray ranges; util_dynarray_init(&ranges, mem_ctx); struct hash_entry *entry; hash_table_foreach(state.blocks, entry) { const int b = entry->hash - 1; const struct ubo_block_info *info = entry->data; uint64_t offsets = info->offsets; /* Walk through the offsets bitfield, finding contiguous regions of * set bits: * * 0000000001111111111111000000000000111111111111110000000011111100 * ^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^ * * Each of these will become a UBO range. */ while (offsets != 0) { /* Find the first 1 in the offsets bitfield. This represents the * start of a range of interesting UBO data. Make it zero-indexed. */ int first_bit = ffsll(offsets) - 1; /* Find the first 0 bit in offsets beyond first_bit. To find the * first zero bit, we find the first 1 bit in the complement. In * order to ignore bits before first_bit, we mask off those bits. */ int first_hole = ffsll(~offsets & ~((1ull << first_bit) - 1)) - 1; if (first_hole == -1) { /* If we didn't find a hole, then set it to the end of the * bitfield. There are no more ranges to process. */ first_hole = 64; offsets = 0; } else { /* We've processed all bits before first_hole. Mask them off. */ offsets &= ~((1ull << first_hole) - 1); } struct ubo_range_entry *entry = util_dynarray_grow(&ranges, sizeof(struct ubo_range_entry)); entry->range.block = b; entry->range.start = first_bit; /* first_hole is one beyond the end, so we don't need to add 1 */ entry->range.length = first_hole - first_bit; entry->benefit = 0; for (int i = 0; i < entry->range.length; i++) entry->benefit += info->uses[first_bit + i]; } } int nr_entries = ranges.size / sizeof(struct ubo_range_entry); if (0) { util_dynarray_foreach(&ranges, struct ubo_range_entry, entry) { print_ubo_entry(stderr, entry, &state); } } /* TODO: Consider combining ranges. * * We can only push 3-4 ranges via 3DSTATE_CONSTANT_XS. If there are * more ranges, and two are close by with only a small hole, it may be * worth combining them. The holes will waste register space, but the * benefit of removing pulls may outweigh that cost. */ /* Sort the list so the most beneficial ranges are at the front. */ qsort(ranges.data, nr_entries, sizeof(struct ubo_range_entry), cmp_ubo_range_entry); struct ubo_range_entry *entries = ranges.data; /* Return the top 4 or so. We drop by one if regular uniforms are in * use, assuming one push buffer will be dedicated to those. We may * also only get 3 on Haswell if we can't write INSTPM. * * The backend may need to shrink these ranges to ensure that they * don't exceed the maximum push constant limits. It can simply drop * the tail of the list, as that's the least valuable portion. We * unfortunately can't truncate it here, because we don't know what * the backend is planning to do with regular uniforms. */ const int max_ubos = (compiler->constant_buffer_0_is_relative ? 3 : 4) - state.uses_regular_uniforms; nr_entries = MIN2(nr_entries, max_ubos); for (int i = 0; i < nr_entries; i++) { out_ranges[i] = entries[i].range; } for (int i = nr_entries; i < 4; i++) { out_ranges[i].block = 0; out_ranges[i].start = 0; out_ranges[i].length = 0; } ralloc_free(ranges.mem_ctx); }