/* * Copyright © 2016 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 "nir.h" #include "nir_builder.h" #include "nir_control_flow.h" #include "nir_loop_analyze.h" /* This limit is chosen fairly arbitrarily. GLSL IR max iteration is 32 * instructions. (Multiply counting nodes and magic number 5.) But there is * no 1:1 mapping between GLSL IR and NIR so 25 was picked because it seemed * to give about the same results. Around 5 instructions per node. But some * loops that would unroll with GLSL IR fail to unroll if we set this to 25 so * we set it to 26. */ #define LOOP_UNROLL_LIMIT 26 /* Prepare this loop for unrolling by first converting to lcssa and then * converting the phis from the top level of the loop body to regs. * Partially converting out of SSA allows us to unroll the loop without having * to keep track of and update phis along the way which gets tricky and * doesn't add much value over converting to regs. * * The loop may have a continue instruction at the end of the loop which does * nothing. Once we're out of SSA, we can safely delete it so we don't have * to deal with it later. */ static void loop_prepare_for_unroll(nir_loop *loop) { nir_rematerialize_derefs_in_use_blocks_impl( nir_cf_node_get_function(&loop->cf_node)); nir_convert_loop_to_lcssa(loop); /* Lower phis at the top level of the loop body */ foreach_list_typed_safe(nir_cf_node, node, node, &loop->body) { if (nir_cf_node_block == node->type) { nir_lower_phis_to_regs_block(nir_cf_node_as_block(node)); } } /* Lower phis after the loop */ nir_block *block_after_loop = nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node)); nir_lower_phis_to_regs_block(block_after_loop); /* Remove continue if its the last instruction in the loop */ nir_instr *last_instr = nir_block_last_instr(nir_loop_last_block(loop)); if (last_instr && last_instr->type == nir_instr_type_jump) { nir_instr_remove(last_instr); } } static void get_first_blocks_in_terminator(nir_loop_terminator *term, nir_block **first_break_block, nir_block **first_continue_block) { if (term->continue_from_then) { *first_continue_block = nir_if_first_then_block(term->nif); *first_break_block = nir_if_first_else_block(term->nif); } else { *first_continue_block = nir_if_first_else_block(term->nif); *first_break_block = nir_if_first_then_block(term->nif); } } /** * Unroll a loop where we know exactly how many iterations there are and there * is only a single exit point. Note here we can unroll loops with multiple * theoretical exits that only have a single terminating exit that we always * know is the "real" exit. * * loop { * ...instrs... * } * * And the iteration count is 3, the output will be: * * ...instrs... ...instrs... ...instrs... */ static void simple_unroll(nir_loop *loop) { nir_loop_terminator *limiting_term = loop->info->limiting_terminator; assert(nir_is_trivial_loop_if(limiting_term->nif, limiting_term->break_block)); loop_prepare_for_unroll(loop); /* Skip over loop terminator and get the loop body. */ list_for_each_entry(nir_loop_terminator, terminator, &loop->info->loop_terminator_list, loop_terminator_link) { /* Remove all but the limiting terminator as we know the other exit * conditions can never be met. Note we need to extract any instructions * in the continue from branch and insert then into the loop body before * removing it. */ if (terminator->nif != limiting_term->nif) { nir_block *first_break_block; nir_block *first_continue_block; get_first_blocks_in_terminator(terminator, &first_break_block, &first_continue_block); assert(nir_is_trivial_loop_if(terminator->nif, terminator->break_block)); nir_cf_list continue_from_lst; nir_cf_extract(&continue_from_lst, nir_before_block(first_continue_block), nir_after_block(terminator->continue_from_block)); nir_cf_reinsert(&continue_from_lst, nir_after_cf_node(&terminator->nif->cf_node)); nir_cf_node_remove(&terminator->nif->cf_node); } } nir_block *first_break_block; nir_block *first_continue_block; get_first_blocks_in_terminator(limiting_term, &first_break_block, &first_continue_block); /* Pluck out the loop header */ nir_block *header_blk = nir_loop_first_block(loop); nir_cf_list lp_header; nir_cf_extract(&lp_header, nir_before_block(header_blk), nir_before_cf_node(&limiting_term->nif->cf_node)); /* Add the continue from block of the limiting terminator to the loop body */ nir_cf_list continue_from_lst; nir_cf_extract(&continue_from_lst, nir_before_block(first_continue_block), nir_after_block(limiting_term->continue_from_block)); nir_cf_reinsert(&continue_from_lst, nir_after_cf_node(&limiting_term->nif->cf_node)); /* Pluck out the loop body */ nir_cf_list loop_body; nir_cf_extract(&loop_body, nir_after_cf_node(&limiting_term->nif->cf_node), nir_after_block(nir_loop_last_block(loop))); struct hash_table *remap_table = _mesa_pointer_hash_table_create(NULL); /* Clone the loop header and insert before the loop */ nir_cf_list_clone_and_reinsert(&lp_header, loop->cf_node.parent, nir_before_cf_node(&loop->cf_node), remap_table); for (unsigned i = 0; i < loop->info->max_trip_count; i++) { /* Clone loop body and insert before the loop */ nir_cf_list_clone_and_reinsert(&loop_body, loop->cf_node.parent, nir_before_cf_node(&loop->cf_node), remap_table); /* Clone loop header and insert after loop body */ nir_cf_list_clone_and_reinsert(&lp_header, loop->cf_node.parent, nir_before_cf_node(&loop->cf_node), remap_table); } /* Remove the break from the loop terminator and add instructions from * the break block after the unrolled loop. */ nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block); nir_instr_remove(break_instr); nir_cf_list break_list; nir_cf_extract(&break_list, nir_before_block(first_break_block), nir_after_block(limiting_term->break_block)); /* Clone so things get properly remapped */ nir_cf_list_clone_and_reinsert(&break_list, loop->cf_node.parent, nir_before_cf_node(&loop->cf_node), remap_table); /* Remove the loop */ nir_cf_node_remove(&loop->cf_node); /* Delete the original loop body, break block & header */ nir_cf_delete(&lp_header); nir_cf_delete(&loop_body); nir_cf_delete(&break_list); _mesa_hash_table_destroy(remap_table, NULL); } static void move_cf_list_into_loop_term(nir_cf_list *lst, nir_loop_terminator *term) { /* Move the rest of the loop inside the continue-from-block */ nir_cf_reinsert(lst, nir_after_block(term->continue_from_block)); /* Remove the break */ nir_instr_remove(nir_block_last_instr(term->break_block)); } static nir_cursor get_complex_unroll_insert_location(nir_cf_node *node, bool continue_from_then) { if (node->type == nir_cf_node_loop) { return nir_before_cf_node(node); } else { nir_if *if_stmt = nir_cf_node_as_if(node); if (continue_from_then) { return nir_after_block(nir_if_last_then_block(if_stmt)); } else { return nir_after_block(nir_if_last_else_block(if_stmt)); } } } static nir_cf_node * complex_unroll_loop_body(nir_loop *loop, nir_loop_terminator *unlimit_term, nir_cf_list *lp_header, nir_cf_list *lp_body, struct hash_table *remap_table, unsigned num_times_to_clone) { /* In the terminator that we have no trip count for move everything after * the terminator into the continue from branch. */ nir_cf_list loop_end; nir_cf_extract(&loop_end, nir_after_cf_node(&unlimit_term->nif->cf_node), nir_after_block(nir_loop_last_block(loop))); move_cf_list_into_loop_term(&loop_end, unlimit_term); /* Pluck out the loop body. */ nir_cf_extract(lp_body, nir_before_block(nir_loop_first_block(loop)), nir_after_block(nir_loop_last_block(loop))); /* Set unroll_loc to the loop as we will insert the unrolled loop before it */ nir_cf_node *unroll_loc = &loop->cf_node; /* Temp list to store the cloned loop as we unroll */ nir_cf_list unrolled_lp_body; for (unsigned i = 0; i < num_times_to_clone; i++) { nir_cursor cursor = get_complex_unroll_insert_location(unroll_loc, unlimit_term->continue_from_then); /* Clone loop header and insert in if branch */ nir_cf_list_clone_and_reinsert(lp_header, loop->cf_node.parent, cursor, remap_table); cursor = get_complex_unroll_insert_location(unroll_loc, unlimit_term->continue_from_then); /* Clone loop body */ nir_cf_list_clone(&unrolled_lp_body, lp_body, loop->cf_node.parent, remap_table); unroll_loc = exec_node_data(nir_cf_node, exec_list_get_tail(&unrolled_lp_body.list), node); assert(unroll_loc->type == nir_cf_node_block && exec_list_is_empty(&nir_cf_node_as_block(unroll_loc)->instr_list)); /* Get the unrolled if node */ unroll_loc = nir_cf_node_prev(unroll_loc); /* Insert unrolled loop body */ nir_cf_reinsert(&unrolled_lp_body, cursor); } return unroll_loc; } /** * Unroll a loop with two exists when the trip count of one of the exits is * unknown. If continue_from_then is true, the loop is repeated only when the * "then" branch of the if is taken; otherwise it is repeated only * when the "else" branch of the if is taken. * * For example, if the input is: * * loop { * ...phis/condition... * if condition { * ...then instructions... * } else { * ...continue instructions... * break * } * ...body... * } * * And the iteration count is 3, and unlimit_term->continue_from_then is true, * then the output will be: * * ...condition... * if condition { * ...then instructions... * ...body... * if condition { * ...then instructions... * ...body... * if condition { * ...then instructions... * ...body... * } else { * ...continue instructions... * } * } else { * ...continue instructions... * } * } else { * ...continue instructions... * } */ static void complex_unroll(nir_loop *loop, nir_loop_terminator *unlimit_term, bool limiting_term_second) { assert(nir_is_trivial_loop_if(unlimit_term->nif, unlimit_term->break_block)); nir_loop_terminator *limiting_term = loop->info->limiting_terminator; assert(nir_is_trivial_loop_if(limiting_term->nif, limiting_term->break_block)); loop_prepare_for_unroll(loop); nir_block *header_blk = nir_loop_first_block(loop); nir_cf_list lp_header; nir_cf_list limit_break_list; unsigned num_times_to_clone; if (limiting_term_second) { /* Pluck out the loop header */ nir_cf_extract(&lp_header, nir_before_block(header_blk), nir_before_cf_node(&unlimit_term->nif->cf_node)); /* We need some special handling when its the second terminator causing * us to exit the loop for example: * * for (int i = 0; i < uniform_lp_count; i++) { * colour = vec4(0.0, 1.0, 0.0, 1.0); * * if (i == 1) { * break; * } * ... any further code is unreachable after i == 1 ... * } */ nir_cf_list after_lt; nir_if *limit_if = limiting_term->nif; nir_cf_extract(&after_lt, nir_after_cf_node(&limit_if->cf_node), nir_after_block(nir_loop_last_block(loop))); move_cf_list_into_loop_term(&after_lt, limiting_term); /* Because the trip count is the number of times we pass over the entire * loop before hitting a break when the second terminator is the * limiting terminator we can actually execute code inside the loop when * trip count == 0 e.g. the code above the break. So we need to bump * the trip_count in order for the code below to clone anything. When * trip count == 1 we execute the code above the break twice and the * code below it once so we need clone things twice and so on. */ num_times_to_clone = loop->info->max_trip_count + 1; } else { /* Pluck out the loop header */ nir_cf_extract(&lp_header, nir_before_block(header_blk), nir_before_cf_node(&limiting_term->nif->cf_node)); nir_block *first_break_block; nir_block *first_continue_block; get_first_blocks_in_terminator(limiting_term, &first_break_block, &first_continue_block); /* Remove the break then extract instructions from the break block so we * can insert them in the innermost else of the unrolled loop. */ nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block); nir_instr_remove(break_instr); nir_cf_extract(&limit_break_list, nir_before_block(first_break_block), nir_after_block(limiting_term->break_block)); nir_cf_list continue_list; nir_cf_extract(&continue_list, nir_before_block(first_continue_block), nir_after_block(limiting_term->continue_from_block)); nir_cf_reinsert(&continue_list, nir_after_cf_node(&limiting_term->nif->cf_node)); nir_cf_node_remove(&limiting_term->nif->cf_node); num_times_to_clone = loop->info->max_trip_count; } struct hash_table *remap_table = _mesa_pointer_hash_table_create(NULL); nir_cf_list lp_body; nir_cf_node *unroll_loc = complex_unroll_loop_body(loop, unlimit_term, &lp_header, &lp_body, remap_table, num_times_to_clone); if (!limiting_term_second) { assert(unroll_loc->type == nir_cf_node_if); nir_cursor cursor = get_complex_unroll_insert_location(unroll_loc, unlimit_term->continue_from_then); /* Clone loop header and insert in if branch */ nir_cf_list_clone_and_reinsert(&lp_header, loop->cf_node.parent, cursor, remap_table); cursor = get_complex_unroll_insert_location(unroll_loc, unlimit_term->continue_from_then); /* Clone so things get properly remapped, and insert break block from * the limiting terminator. */ nir_cf_list_clone_and_reinsert(&limit_break_list, loop->cf_node.parent, cursor, remap_table); nir_cf_delete(&limit_break_list); } /* The loop has been unrolled so remove it. */ nir_cf_node_remove(&loop->cf_node); /* Delete the original loop header and body */ nir_cf_delete(&lp_header); nir_cf_delete(&lp_body); _mesa_hash_table_destroy(remap_table, NULL); } /* Unrolls the classic wrapper loops e.g * * do { * // ... * } while (false) */ static bool wrapper_unroll(nir_loop *loop) { if (!list_empty(&loop->info->loop_terminator_list)) { /* Unrolling a loop with a large number of exits can result in a * large inrease in register pressure. For now we just skip * unrolling if we have more than 3 exits (not including the break * at the end of the loop). * * TODO: Most loops that fit this pattern are simply switch * statements that are converted to a loop to take advantage of * exiting jump instruction handling. In this case we could make * use of a binary seach pattern like we do in * nir_lower_indirect_derefs(), this should allow us to unroll the * loops in an optimal way and should also avoid some of the * register pressure that comes from simply nesting the * terminators one after the other. */ if (list_length(&loop->info->loop_terminator_list) > 3) return false; loop_prepare_for_unroll(loop); nir_cursor loop_end = nir_after_block(nir_loop_last_block(loop)); list_for_each_entry(nir_loop_terminator, terminator, &loop->info->loop_terminator_list, loop_terminator_link) { /* Remove break from the terminator */ nir_instr *break_instr = nir_block_last_instr(terminator->break_block); nir_instr_remove(break_instr); /* Pluck out the loop body. */ nir_cf_list loop_body; nir_cf_extract(&loop_body, nir_after_cf_node(&terminator->nif->cf_node), loop_end); /* Reinsert loop body into continue from block */ nir_cf_reinsert(&loop_body, nir_after_block(terminator->continue_from_block)); loop_end = terminator->continue_from_then ? nir_after_block(nir_if_last_then_block(terminator->nif)) : nir_after_block(nir_if_last_else_block(terminator->nif)); } } else { nir_block *blk_after_loop = nir_cursor_current_block(nir_after_cf_node(&loop->cf_node)); /* There may still be some single src phis following the loop that * have not yet been cleaned up by another pass. Tidy those up * before unrolling the loop. */ nir_foreach_instr_safe(instr, blk_after_loop) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); assert(exec_list_length(&phi->srcs) == 1); nir_phi_src *phi_src = exec_node_data(nir_phi_src, exec_list_get_head(&phi->srcs), node); nir_ssa_def_rewrite_uses(&phi->dest.ssa, phi_src->src); nir_instr_remove(instr); } /* Remove break at end of the loop */ nir_block *last_loop_blk = nir_loop_last_block(loop); nir_instr *break_instr = nir_block_last_instr(last_loop_blk); nir_instr_remove(break_instr); } /* Pluck out the loop body. */ nir_cf_list loop_body; nir_cf_extract(&loop_body, nir_before_block(nir_loop_first_block(loop)), nir_after_block(nir_loop_last_block(loop))); /* Reinsert loop body after the loop */ nir_cf_reinsert(&loop_body, nir_after_cf_node(&loop->cf_node)); /* The loop has been unrolled so remove it. */ nir_cf_node_remove(&loop->cf_node); return true; } static bool is_loop_small_enough_to_unroll(nir_shader *shader, nir_loop_info *li) { unsigned max_iter = shader->options->max_unroll_iterations; if (li->max_trip_count > max_iter) return false; if (li->force_unroll) return true; bool loop_not_too_large = li->instr_cost * li->max_trip_count <= max_iter * LOOP_UNROLL_LIMIT; return loop_not_too_large; } static bool process_loops(nir_shader *sh, nir_cf_node *cf_node, bool *has_nested_loop_out) { bool progress = false; bool has_nested_loop = false; nir_loop *loop; switch (cf_node->type) { case nir_cf_node_block: return progress; case nir_cf_node_if: { nir_if *if_stmt = nir_cf_node_as_if(cf_node); foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->then_list) progress |= process_loops(sh, nested_node, has_nested_loop_out); foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->else_list) progress |= process_loops(sh, nested_node, has_nested_loop_out); return progress; } case nir_cf_node_loop: { loop = nir_cf_node_as_loop(cf_node); foreach_list_typed_safe(nir_cf_node, nested_node, node, &loop->body) progress |= process_loops(sh, nested_node, &has_nested_loop); break; } default: unreachable("unknown cf node type"); } /* Don't attempt to unroll a second inner loop in this pass, wait until the * next pass as we have altered the cf. */ if (!progress) { /* Check for the classic * * do { * // ... * } while (false) * * that is used to wrap multi-line macros. GLSL IR also wraps switch * statements in a loop like this. */ if (loop->info->limiting_terminator == NULL && !loop->info->complex_loop) { nir_block *last_loop_blk = nir_loop_last_block(loop); if (!nir_block_ends_in_break(last_loop_blk)) goto exit; progress = wrapper_unroll(loop); goto exit; } if (has_nested_loop || loop->info->limiting_terminator == NULL) goto exit; if (!is_loop_small_enough_to_unroll(sh, loop->info)) goto exit; if (loop->info->exact_trip_count_known) { simple_unroll(loop); progress = true; } else { /* Attempt to unroll loops with two terminators. */ unsigned num_lt = list_length(&loop->info->loop_terminator_list); if (num_lt == 2) { bool limiting_term_second = true; nir_loop_terminator *terminator = list_first_entry(&loop->info->loop_terminator_list, nir_loop_terminator, loop_terminator_link); if (terminator->nif == loop->info->limiting_terminator->nif) { limiting_term_second = false; terminator = list_last_entry(&loop->info->loop_terminator_list, nir_loop_terminator, loop_terminator_link); } /* If the first terminator has a trip count of zero and is the * limiting terminator just do a simple unroll as the second * terminator can never be reached. */ if (loop->info->max_trip_count == 0 && !limiting_term_second) { simple_unroll(loop); } else { complex_unroll(loop, terminator, limiting_term_second); } progress = true; } } } exit: *has_nested_loop_out = true; return progress; } static bool nir_opt_loop_unroll_impl(nir_function_impl *impl, nir_variable_mode indirect_mask) { bool progress = false; nir_metadata_require(impl, nir_metadata_loop_analysis, indirect_mask); nir_metadata_require(impl, nir_metadata_block_index); foreach_list_typed_safe(nir_cf_node, node, node, &impl->body) { bool has_nested_loop = false; progress |= process_loops(impl->function->shader, node, &has_nested_loop); } if (progress) nir_lower_regs_to_ssa_impl(impl); return progress; } /** * indirect_mask specifies which type of indirectly accessed variables * should force loop unrolling. */ bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask) { bool progress = false; nir_foreach_function(function, shader) { if (function->impl) { progress |= nir_opt_loop_unroll_impl(function->impl, indirect_mask); } } return progress; }