/* * Copyright © 2015 Thomas Helland * * 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_constant_expressions.h" #include "nir_loop_analyze.h" typedef enum { undefined, invariant, not_invariant, basic_induction } nir_loop_variable_type; struct nir_basic_induction_var; typedef struct { /* A link for the work list */ struct list_head process_link; bool in_loop; /* The ssa_def associated with this info */ nir_ssa_def *def; /* The type of this ssa_def */ nir_loop_variable_type type; /* If this is of type basic_induction */ struct nir_basic_induction_var *ind; /* True if variable is in an if branch or a nested loop */ bool in_control_flow; } nir_loop_variable; typedef struct nir_basic_induction_var { nir_op alu_op; /* The type of alu-operation */ nir_loop_variable *alu_def; /* The def of the alu-operation */ nir_loop_variable *invariant; /* The invariant alu-operand */ nir_loop_variable *def_outside_loop; /* The phi-src outside the loop */ } nir_basic_induction_var; typedef struct { /* The loop we store information for */ nir_loop *loop; /* Loop_variable for all ssa_defs in function */ nir_loop_variable *loop_vars; /* A list of the loop_vars to analyze */ struct list_head process_list; nir_variable_mode indirect_mask; } loop_info_state; static nir_loop_variable * get_loop_var(nir_ssa_def *value, loop_info_state *state) { return &(state->loop_vars[value->index]); } typedef struct { loop_info_state *state; bool in_control_flow; } init_loop_state; static bool init_loop_def(nir_ssa_def *def, void *void_init_loop_state) { init_loop_state *loop_init_state = void_init_loop_state; nir_loop_variable *var = get_loop_var(def, loop_init_state->state); if (loop_init_state->in_control_flow) { var->in_control_flow = true; } else { /* Add to the tail of the list. That way we start at the beginning of * the defs in the loop instead of the end when walking the list. This * means less recursive calls. Only add defs that are not in nested * loops or conditional blocks. */ list_addtail(&var->process_link, &loop_init_state->state->process_list); } var->in_loop = true; return true; } static bool init_loop_block(nir_block *block, loop_info_state *state, bool in_control_flow) { init_loop_state init_state = {.in_control_flow = in_control_flow, .state = state }; nir_foreach_instr(instr, block) { if (instr->type == nir_instr_type_intrinsic || instr->type == nir_instr_type_alu || instr->type == nir_instr_type_tex) { state->loop->info->num_instructions++; } nir_foreach_ssa_def(instr, init_loop_def, &init_state); } return true; } static inline bool is_var_alu(nir_loop_variable *var) { return var->def->parent_instr->type == nir_instr_type_alu; } static inline bool is_var_constant(nir_loop_variable *var) { return var->def->parent_instr->type == nir_instr_type_load_const; } static inline bool is_var_phi(nir_loop_variable *var) { return var->def->parent_instr->type == nir_instr_type_phi; } static inline bool mark_invariant(nir_ssa_def *def, loop_info_state *state) { nir_loop_variable *var = get_loop_var(def, state); if (var->type == invariant) return true; if (!var->in_loop) { var->type = invariant; return true; } if (var->type == not_invariant) return false; if (is_var_alu(var)) { nir_alu_instr *alu = nir_instr_as_alu(def->parent_instr); for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) { if (!mark_invariant(alu->src[i].src.ssa, state)) { var->type = not_invariant; return false; } } var->type = invariant; return true; } /* Phis shouldn't be invariant except if one operand is invariant, and the * other is the phi itself. These should be removed by opt_remove_phis. * load_consts are already set to invariant and constant during init, * and so should return earlier. Remaining op_codes are set undefined. */ var->type = not_invariant; return false; } static void compute_invariance_information(loop_info_state *state) { /* An expression is invariant in a loop L if: * (base cases) * – it’s a constant * – it’s a variable use, all of whose single defs are outside of L * (inductive cases) * – it’s a pure computation all of whose args are loop invariant * – it’s a variable use whose single reaching def, and the * rhs of that def is loop-invariant */ list_for_each_entry_safe(nir_loop_variable, var, &state->process_list, process_link) { assert(!var->in_control_flow); if (mark_invariant(var->def, state)) list_del(&var->process_link); } } static bool compute_induction_information(loop_info_state *state) { bool found_induction_var = false; list_for_each_entry_safe(nir_loop_variable, var, &state->process_list, process_link) { /* It can't be an induction variable if it is invariant. Invariants and * things in nested loops or conditionals should have been removed from * the list by compute_invariance_information(). */ assert(!var->in_control_flow && var->type != invariant); /* We are only interested in checking phi's for the basic induction * variable case as its simple to detect. All basic induction variables * have a phi node */ if (!is_var_phi(var)) continue; nir_phi_instr *phi = nir_instr_as_phi(var->def->parent_instr); nir_basic_induction_var *biv = rzalloc(state, nir_basic_induction_var); nir_foreach_phi_src(src, phi) { nir_loop_variable *src_var = get_loop_var(src->src.ssa, state); /* If one of the sources is in a conditional or nested block then * panic. */ if (src_var->in_control_flow) break; if (!src_var->in_loop) { biv->def_outside_loop = src_var; } else if (is_var_alu(src_var)) { nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr); if (nir_op_infos[alu->op].num_inputs == 2) { biv->alu_def = src_var; biv->alu_op = alu->op; for (unsigned i = 0; i < 2; i++) { /* Is one of the operands const, and the other the phi */ if (alu->src[i].src.ssa->parent_instr->type == nir_instr_type_load_const && alu->src[1-i].src.ssa == &phi->dest.ssa) biv->invariant = get_loop_var(alu->src[i].src.ssa, state); } } } } if (biv->alu_def && biv->def_outside_loop && biv->invariant && is_var_constant(biv->def_outside_loop)) { assert(is_var_constant(biv->invariant)); biv->alu_def->type = basic_induction; biv->alu_def->ind = biv; var->type = basic_induction; var->ind = biv; found_induction_var = true; } else { ralloc_free(biv); } } return found_induction_var; } static bool initialize_ssa_def(nir_ssa_def *def, void *void_state) { loop_info_state *state = void_state; nir_loop_variable *var = get_loop_var(def, state); var->in_loop = false; var->def = def; if (def->parent_instr->type == nir_instr_type_load_const) { var->type = invariant; } else { var->type = undefined; } return true; } static inline bool ends_in_break(nir_block *block) { if (exec_list_is_empty(&block->instr_list)) return false; nir_instr *instr = nir_block_last_instr(block); return instr->type == nir_instr_type_jump && nir_instr_as_jump(instr)->type == nir_jump_break; } static bool find_loop_terminators(loop_info_state *state) { bool success = false; foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) { if (node->type == nir_cf_node_if) { nir_if *nif = nir_cf_node_as_if(node); nir_block *break_blk = NULL; nir_block *continue_from_blk = NULL; bool continue_from_then = true; nir_block *last_then = nir_if_last_then_block(nif); nir_block *last_else = nir_if_last_else_block(nif); if (ends_in_break(last_then)) { break_blk = last_then; continue_from_blk = last_else; continue_from_then = false; } else if (ends_in_break(last_else)) { break_blk = last_else; continue_from_blk = last_then; } /* If there is a break then we should find a terminator. If we can * not find a loop terminator, but there is a break-statement then * we should return false so that we do not try to find trip-count */ if (!nir_is_trivial_loop_if(nif, break_blk)) return false; /* Continue if the if contained no jumps at all */ if (!break_blk) continue; if (nif->condition.ssa->parent_instr->type == nir_instr_type_phi) return false; nir_loop_terminator *terminator = rzalloc(state->loop->info, nir_loop_terminator); list_add(&terminator->loop_terminator_link, &state->loop->info->loop_terminator_list); terminator->nif = nif; terminator->break_block = break_blk; terminator->continue_from_block = continue_from_blk; terminator->continue_from_then = continue_from_then; terminator->conditional_instr = nif->condition.ssa->parent_instr; success = true; } } return success; } static int32_t get_iteration(nir_op cond_op, nir_const_value *initial, nir_const_value *step, nir_const_value *limit, nir_alu_instr *alu) { int32_t iter; switch (cond_op) { case nir_op_ige: case nir_op_ilt: case nir_op_ieq: case nir_op_ine: { int32_t initial_val = initial->i32[0]; int32_t span = limit->i32[0] - initial_val; iter = span / step->i32[0]; break; } case nir_op_uge: case nir_op_ult: { uint32_t initial_val = initial->u32[0]; uint32_t span = limit->u32[0] - initial_val; iter = span / step->u32[0]; break; } case nir_op_fge: case nir_op_flt: case nir_op_feq: case nir_op_fne: { float initial_val = initial->f32[0]; float span = limit->f32[0] - initial_val; iter = span / step->f32[0]; break; } default: return -1; } return iter; } static bool test_iterations(int32_t iter_int, nir_const_value *step, nir_const_value *limit, nir_op cond_op, unsigned bit_size, nir_alu_type induction_base_type, nir_const_value *initial, bool limit_rhs, bool invert_cond) { assert(nir_op_infos[cond_op].num_inputs == 2); nir_const_value iter_src = { {0, } }; nir_op mul_op; nir_op add_op; switch (induction_base_type) { case nir_type_float: iter_src.f32[0] = (float) iter_int; mul_op = nir_op_fmul; add_op = nir_op_fadd; break; case nir_type_int: case nir_type_uint: iter_src.i32[0] = iter_int; mul_op = nir_op_imul; add_op = nir_op_iadd; break; default: unreachable("Unhandled induction variable base type!"); } /* Multiple the iteration count we are testing by the number of times we * step the induction variable each iteration. */ nir_const_value mul_src[2] = { iter_src, *step }; nir_const_value mul_result = nir_eval_const_opcode(mul_op, 1, bit_size, mul_src); /* Add the initial value to the accumulated induction variable total */ nir_const_value add_src[2] = { mul_result, *initial }; nir_const_value add_result = nir_eval_const_opcode(add_op, 1, bit_size, add_src); nir_const_value src[2] = { { {0, } }, { {0, } } }; src[limit_rhs ? 0 : 1] = add_result; src[limit_rhs ? 1 : 0] = *limit; /* Evaluate the loop exit condition */ nir_const_value result = nir_eval_const_opcode(cond_op, 1, bit_size, src); return invert_cond ? (result.u32[0] == 0) : (result.u32[0] != 0); } static int calculate_iterations(nir_const_value *initial, nir_const_value *step, nir_const_value *limit, nir_loop_variable *alu_def, nir_alu_instr *cond_alu, bool limit_rhs, bool invert_cond) { assert(initial != NULL && step != NULL && limit != NULL); nir_alu_instr *alu = nir_instr_as_alu(alu_def->def->parent_instr); /* nir_op_isub should have been lowered away by this point */ assert(alu->op != nir_op_isub); /* Make sure the alu type for our induction variable is compatible with the * conditional alus input type. If its not something has gone really wrong. */ nir_alu_type induction_base_type = nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type); if (induction_base_type == nir_type_int || induction_base_type == nir_type_uint) { assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_int || nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_uint); } else { assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[0]) == induction_base_type); } /* Check for nsupported alu operations */ if (alu->op != nir_op_iadd && alu->op != nir_op_fadd) return -1; /* do-while loops can increment the starting value before the condition is * checked. e.g. * * do { * ndx++; * } while (ndx < 3); * * Here we check if the induction variable is used directly by the loop * condition and if so we assume we need to step the initial value. */ unsigned trip_offset = 0; if (cond_alu->src[0].src.ssa == alu_def->def || cond_alu->src[1].src.ssa == alu_def->def) { trip_offset = 1; } int iter_int = get_iteration(cond_alu->op, initial, step, limit, alu); /* If iter_int is negative the loop is ill-formed or is the conditional is * unsigned with a huge iteration count so don't bother going any further. */ if (iter_int < 0) return -1; /* An explanation from the GLSL unrolling pass: * * Make sure that the calculated number of iterations satisfies the exit * condition. This is needed to catch off-by-one errors and some types of * ill-formed loops. For example, we need to detect that the following * loop does not have a maximum iteration count. * * for (float x = 0.0; x != 0.9; x += 0.2); */ assert(nir_src_bit_size(alu->src[0].src) == nir_src_bit_size(alu->src[1].src)); unsigned bit_size = nir_src_bit_size(alu->src[0].src); for (int bias = -1; bias <= 1; bias++) { const int iter_bias = iter_int + bias; if (test_iterations(iter_bias, step, limit, cond_alu->op, bit_size, induction_base_type, initial, limit_rhs, invert_cond)) { return iter_bias > 0 ? iter_bias - trip_offset : iter_bias; } } return -1; } /* Run through each of the terminators of the loop and try to infer a possible * trip-count. We need to check them all, and set the lowest trip-count as the * trip-count of our loop. If one of the terminators has an undecidable * trip-count we can not safely assume anything about the duration of the * loop. */ static void find_trip_count(loop_info_state *state) { bool trip_count_known = true; nir_loop_terminator *limiting_terminator = NULL; int min_trip_count = -1; list_for_each_entry(nir_loop_terminator, terminator, &state->loop->info->loop_terminator_list, loop_terminator_link) { if (terminator->conditional_instr->type != nir_instr_type_alu) { /* If we get here the loop is dead and will get cleaned up by the * nir_opt_dead_cf pass. */ trip_count_known = false; continue; } nir_alu_instr *alu = nir_instr_as_alu(terminator->conditional_instr); nir_loop_variable *basic_ind = NULL; nir_loop_variable *limit = NULL; bool limit_rhs = true; switch (alu->op) { case nir_op_fge: case nir_op_ige: case nir_op_uge: case nir_op_flt: case nir_op_ilt: case nir_op_ult: case nir_op_feq: case nir_op_ieq: case nir_op_fne: case nir_op_ine: /* We assume that the limit is the "right" operand */ basic_ind = get_loop_var(alu->src[0].src.ssa, state); limit = get_loop_var(alu->src[1].src.ssa, state); if (basic_ind->type != basic_induction) { /* We had it the wrong way, flip things around */ basic_ind = get_loop_var(alu->src[1].src.ssa, state); limit = get_loop_var(alu->src[0].src.ssa, state); limit_rhs = false; } /* The comparison has to have a basic induction variable * and a constant for us to be able to find trip counts */ if (basic_ind->type != basic_induction || !is_var_constant(limit)) { trip_count_known = false; continue; } /* We have determined that we have the following constants: * (With the typical int i = 0; i < x; i++; as an example) * - Upper limit. * - Starting value * - Step / iteration size * Thats all thats needed to calculate the trip-count */ nir_const_value initial_val = nir_instr_as_load_const(basic_ind->ind->def_outside_loop-> def->parent_instr)->value; nir_const_value step_val = nir_instr_as_load_const(basic_ind->ind->invariant->def-> parent_instr)->value; nir_const_value limit_val = nir_instr_as_load_const(limit->def->parent_instr)->value; int iterations = calculate_iterations(&initial_val, &step_val, &limit_val, basic_ind->ind->alu_def, alu, limit_rhs, terminator->continue_from_then); /* Where we not able to calculate the iteration count */ if (iterations == -1) { trip_count_known = false; continue; } /* If this is the first run or we have found a smaller amount of * iterations than previously (we have identified a more limiting * terminator) set the trip count and limiting terminator. */ if (min_trip_count == -1 || iterations < min_trip_count) { min_trip_count = iterations; limiting_terminator = terminator; } break; default: trip_count_known = false; } } state->loop->info->is_trip_count_known = trip_count_known; if (min_trip_count > -1) state->loop->info->trip_count = min_trip_count; state->loop->info->limiting_terminator = limiting_terminator; } /* Checks if we should force the loop to be unrolled regardless of size * due to array access heuristics. */ static bool force_unroll_array_access(loop_info_state *state, nir_shader *ns, nir_deref_var *variable) { nir_deref *tail = &variable->deref; while (tail->child != NULL) { tail = tail->child; if (tail->deref_type == nir_deref_type_array) { nir_deref_array *deref_array = nir_deref_as_array(tail); if (deref_array->deref_array_type != nir_deref_array_type_indirect) continue; nir_loop_variable *array_index = get_loop_var(deref_array->indirect.ssa, state); if (array_index->type != basic_induction) continue; /* If an array is indexed by a loop induction variable, and the * array size is exactly the number of loop iterations, this is * probably a simple for-loop trying to access each element in * turn; the application may expect it to be unrolled. */ if (glsl_get_length(variable->deref.type) == state->loop->info->trip_count) { state->loop->info->force_unroll = true; return state->loop->info->force_unroll; } if (variable->var->data.mode & state->indirect_mask) { state->loop->info->force_unroll = true; return state->loop->info->force_unroll; } } } return false; } static bool force_unroll_heuristics(loop_info_state *state, nir_shader *ns, 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); /* Check for arrays variably-indexed by a loop induction variable. * Unrolling the loop may convert that access into constant-indexing. */ if (intrin->intrinsic == nir_intrinsic_load_var || intrin->intrinsic == nir_intrinsic_store_var || intrin->intrinsic == nir_intrinsic_copy_var) { unsigned num_vars = nir_intrinsic_infos[intrin->intrinsic].num_variables; for (unsigned i = 0; i < num_vars; i++) { if (force_unroll_array_access(state, ns, intrin->variables[i])) return true; } } } return false; } static void get_loop_info(loop_info_state *state, nir_function_impl *impl) { /* Initialize all variables to "outside_loop". This also marks defs * invariant and constant if they are nir_instr_type_load_const's */ nir_foreach_block(block, impl) { nir_foreach_instr(instr, block) nir_foreach_ssa_def(instr, initialize_ssa_def, state); } /* Add all entries in the outermost part of the loop to the processing list * Mark the entries in conditionals or in nested loops accordingly */ foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) { switch (node->type) { case nir_cf_node_block: init_loop_block(nir_cf_node_as_block(node), state, false); break; case nir_cf_node_if: nir_foreach_block_in_cf_node(block, node) init_loop_block(block, state, true); break; case nir_cf_node_loop: nir_foreach_block_in_cf_node(block, node) { init_loop_block(block, state, true); } break; case nir_cf_node_function: break; } } /* Induction analysis needs invariance information so get that first */ compute_invariance_information(state); /* We have invariance information so try to find induction variables */ if (!compute_induction_information(state)) return; /* Try to find all simple terminators of the loop. If we can't find any, * or we find possible terminators that have side effects then bail. */ if (!find_loop_terminators(state)) { list_for_each_entry_safe(nir_loop_terminator, terminator, &state->loop->info->loop_terminator_list, loop_terminator_link) { list_del(&terminator->loop_terminator_link); ralloc_free(terminator); } return; } /* Run through each of the terminators and try to compute a trip-count */ find_trip_count(state); nir_shader *ns = impl->function->shader; foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) { if (node->type == nir_cf_node_block) { if (force_unroll_heuristics(state, ns, nir_cf_node_as_block(node))) break; } else { nir_foreach_block_in_cf_node(block, node) { if (force_unroll_heuristics(state, ns, block)) break; } } } } static loop_info_state * initialize_loop_info_state(nir_loop *loop, void *mem_ctx, nir_function_impl *impl) { loop_info_state *state = rzalloc(mem_ctx, loop_info_state); state->loop_vars = rzalloc_array(mem_ctx, nir_loop_variable, impl->ssa_alloc); state->loop = loop; list_inithead(&state->process_list); if (loop->info) ralloc_free(loop->info); loop->info = rzalloc(loop, nir_loop_info); list_inithead(&loop->info->loop_terminator_list); return state; } static void process_loops(nir_cf_node *cf_node, nir_variable_mode indirect_mask) { switch (cf_node->type) { case nir_cf_node_block: return; case nir_cf_node_if: { nir_if *if_stmt = nir_cf_node_as_if(cf_node); foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->then_list) process_loops(nested_node, indirect_mask); foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list) process_loops(nested_node, indirect_mask); return; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(cf_node); foreach_list_typed(nir_cf_node, nested_node, node, &loop->body) process_loops(nested_node, indirect_mask); break; } default: unreachable("unknown cf node type"); } nir_loop *loop = nir_cf_node_as_loop(cf_node); nir_function_impl *impl = nir_cf_node_get_function(cf_node); void *mem_ctx = ralloc_context(NULL); loop_info_state *state = initialize_loop_info_state(loop, mem_ctx, impl); state->indirect_mask = indirect_mask; get_loop_info(state, impl); ralloc_free(mem_ctx); } void nir_loop_analyze_impl(nir_function_impl *impl, nir_variable_mode indirect_mask) { nir_index_ssa_defs(impl); foreach_list_typed(nir_cf_node, node, node, &impl->body) process_loops(node, indirect_mask); }