/* * Copyright (C) 2019 Collabora, Ltd. * * 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. * * Authors (Collabora): * Alyssa Rosenzweig */ #include "compiler.h" #include "util/u_math.h" #include "util/u_memory.h" /* This pass promotes reads from uniforms from load/store ops to uniform * registers if it is beneficial to do so. Normally, this saves both * instructions and total register pressure, but it does take a toll on the * number of work registers that are available, so this is a balance. * * We use a heuristic to determine the ideal count, implemented by * mir_work_heuristic, which returns the ideal number of work registers. */ static bool mir_is_promoteable_ubo(midgard_instruction *ins) { /* TODO: promote unaligned access via swizzle? */ return (ins->type == TAG_LOAD_STORE_4) && (OP_IS_UBO_READ(ins->load_store.op)) && !(ins->constants.u32[0] & 0xF) && !(ins->load_store.arg_1) && (ins->load_store.arg_2 == 0x1E) && ((ins->constants.u32[0] / 16) < 16); } static unsigned mir_promoteable_uniform_count(compiler_context *ctx) { unsigned count = 0; mir_foreach_instr_global(ctx, ins) { if (mir_is_promoteable_ubo(ins)) count = MAX2(count, ins->constants.u32[0] / 16); } return count; } static unsigned mir_count_live(uint16_t *live, unsigned temp_count) { unsigned count = 0; for (unsigned i = 0; i < temp_count; ++i) count += util_bitcount(live[i]); return count; } static unsigned mir_estimate_pressure(compiler_context *ctx) { mir_invalidate_liveness(ctx); mir_compute_liveness(ctx); unsigned max_live = 0; mir_foreach_block(ctx, _block) { midgard_block *block = (midgard_block *) _block; uint16_t *live = mem_dup(block->base.live_out, ctx->temp_count * sizeof(uint16_t)); mir_foreach_instr_in_block_rev(block, ins) { unsigned count = mir_count_live(live, ctx->temp_count); max_live = MAX2(max_live, count); mir_liveness_ins_update(live, ins, ctx->temp_count); } free(live); } return DIV_ROUND_UP(max_live, 16); } static unsigned mir_work_heuristic(compiler_context *ctx) { unsigned uniform_count = mir_promoteable_uniform_count(ctx); /* If there are 8 or fewer uniforms, it doesn't matter what we do, so * allow as many work registers as needed */ if (uniform_count <= 8) return 16; /* Otherwise, estimate the register pressure */ unsigned pressure = mir_estimate_pressure(ctx); /* Prioritize not spilling above all else. The relation between the * pressure estimate and the actual register pressure is a little * murkier than we might like (due to scheduling, pipeline registers, * failure to pack vector registers, load/store registers, texture * registers...), hence why this is a heuristic parameter */ if (pressure > 6) return 16; /* If there's no chance of spilling, prioritize UBOs and thread count */ return 8; } /* Bitset of indices that will be used as a special register -- inputs to a * non-ALU op. We precompute this set so that testing is efficient, otherwise * we end up O(mn) behaviour for n instructions and m uniform reads */ static BITSET_WORD * mir_special_indices(compiler_context *ctx) { mir_compute_temp_count(ctx); BITSET_WORD *bset = calloc(BITSET_WORDS(ctx->temp_count), sizeof(BITSET_WORD)); mir_foreach_instr_global(ctx, ins) { /* Look for special instructions */ bool is_ldst = ins->type == TAG_LOAD_STORE_4; bool is_tex = ins->type == TAG_TEXTURE_4; bool is_writeout = ins->compact_branch && ins->writeout; if (!(is_ldst || is_tex || is_writeout)) continue; /* Anything read by a special instruction is itself special */ mir_foreach_src(ins, i) { unsigned idx = ins->src[i]; if (idx < ctx->temp_count) BITSET_SET(bset, idx); } } return bset; } void midgard_promote_uniforms(compiler_context *ctx) { unsigned work_count = mir_work_heuristic(ctx); unsigned promoted_count = 24 - work_count; /* First, figure out special indices a priori so we don't recompute a lot */ BITSET_WORD *special = mir_special_indices(ctx); mir_foreach_instr_global_safe(ctx, ins) { if (!mir_is_promoteable_ubo(ins)) continue; unsigned off = ins->constants.u32[0]; unsigned address = off / 16; /* Check if it's a promotable range */ unsigned uniform_reg = 23 - address; if (address >= promoted_count) continue; /* It is, great! Let's promote */ ctx->uniform_cutoff = MAX2(ctx->uniform_cutoff, address + 1); unsigned promoted = SSA_FIXED_REGISTER(uniform_reg); /* We do need the move for safety for a non-SSA dest, or if * we're being fed into a special class */ bool needs_move = ins->dest & PAN_IS_REG; if (ins->dest < ctx->temp_count) needs_move |= BITSET_TEST(special, ins->dest); if (needs_move) { unsigned type_size = nir_alu_type_get_type_size(ins->dest_type); midgard_instruction mov = v_mov(promoted, ins->dest); if (type_size == 64) mov.alu.reg_mode = midgard_reg_mode_64; uint16_t rounded = mir_round_bytemask_up(mir_bytemask(ins), type_size); mir_set_bytemask(&mov, rounded); mir_insert_instruction_before(ctx, ins, mov); } else { mir_rewrite_index_src(ctx, ins->dest, promoted); } mir_remove_instruction(ins); } free(special); }