--- /dev/null
+/*
+ * 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);
+ if (intrin->intrinsic == nir_intrinsic_load_uniform)
+ state->uses_regular_uniforms = true;
+
+ if (intrin->intrinsic != nir_intrinsic_load_ubo)
+ continue;
+
+ 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;
+
+ /* Won't fit in our bitfield */
+ if (offset >= 64)
+ continue;
+
+ /* TODO: should we count uses in loops as higher benefit? */
+
+ struct ubo_block_info *info = get_block_info(state, block);
+ info->offsets |= 1ull << 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 = %zx, "
+ "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,
+ 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->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),
+ };
+
+ /* 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);
+}
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