/* * 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; typedef struct nir_basic_induction_var { nir_alu_instr *alu; /* The def of the alu-operation */ nir_ssa_def *def_outside_loop; /* The phi-src outside the loop */ } 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 */ bool in_if_branch; /* True if variable is in a nested loop */ bool in_nested_loop; } nir_loop_variable; 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_if_branch; bool in_nested_loop; } 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_nested_loop) { var->in_nested_loop = true; } else if (loop_init_state->in_if_branch) { var->in_if_branch = 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; } /** Calculate an estimated cost in number of instructions * * We do this so that we don't unroll loops which will later get massively * inflated due to int64 or fp64 lowering. The estimates provided here don't * have to be massively accurate; they just have to be good enough that loop * unrolling doesn't cause things to blow up too much. */ static unsigned instr_cost(nir_instr *instr, const nir_shader_compiler_options *options) { if (instr->type == nir_instr_type_intrinsic || instr->type == nir_instr_type_tex) return 1; if (instr->type != nir_instr_type_alu) return 0; nir_alu_instr *alu = nir_instr_as_alu(instr); const nir_op_info *info = &nir_op_infos[alu->op]; /* Assume everything 16 or 32-bit is cheap. * * There are no 64-bit ops that don't have a 64-bit thing as their * destination or first source. */ if (nir_dest_bit_size(alu->dest.dest) < 64 && nir_src_bit_size(alu->src[0].src) < 64) return 1; bool is_fp64 = nir_dest_bit_size(alu->dest.dest) == 64 && nir_alu_type_get_base_type(info->output_type) == nir_type_float; for (unsigned i = 0; i < info->num_inputs; i++) { if (nir_src_bit_size(alu->src[i].src) == 64 && nir_alu_type_get_base_type(info->input_types[i]) == nir_type_float) is_fp64 = true; } if (is_fp64) { /* If it's something lowered normally, it's expensive. */ unsigned cost = 1; if (options->lower_doubles_options & nir_lower_doubles_op_to_options_mask(alu->op)) cost *= 20; /* If it's full software, it's even more expensive */ if (options->lower_doubles_options & nir_lower_fp64_full_software) cost *= 100; return cost; } else { if (options->lower_int64_options & nir_lower_int64_op_to_options_mask(alu->op)) { /* These require a doing the division algorithm. */ if (alu->op == nir_op_idiv || alu->op == nir_op_udiv || alu->op == nir_op_imod || alu->op == nir_op_umod || alu->op == nir_op_irem) return 100; /* Other int64 lowering isn't usually all that expensive */ return 5; } return 1; } } static bool init_loop_block(nir_block *block, loop_info_state *state, bool in_if_branch, bool in_nested_loop, const nir_shader_compiler_options *options) { init_loop_state init_state = {.in_if_branch = in_if_branch, .in_nested_loop = in_nested_loop, .state = state }; nir_foreach_instr(instr, block) { state->loop->info->instr_cost += instr_cost(instr, options); 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_if_branch && !var->in_nested_loop); if (mark_invariant(var->def, state)) list_del(&var->process_link); } } /* If all of the instruction sources point to identical ALU instructions (as * per nir_instrs_equal), return one of the ALU instructions. Otherwise, * return NULL. */ static nir_alu_instr * phi_instr_as_alu(nir_phi_instr *phi) { nir_alu_instr *first = NULL; nir_foreach_phi_src(src, phi) { assert(src->src.is_ssa); if (src->src.ssa->parent_instr->type != nir_instr_type_alu) return NULL; nir_alu_instr *alu = nir_instr_as_alu(src->src.ssa->parent_instr); if (first == NULL) { first = alu; } else { if (!nir_instrs_equal(&first->instr, &alu->instr)) return NULL; } } return first; } static bool alu_src_has_identity_swizzle(nir_alu_instr *alu, unsigned src_idx) { assert(nir_op_infos[alu->op].input_sizes[src_idx] == 0); assert(alu->dest.dest.is_ssa); for (unsigned i = 0; i < alu->dest.dest.ssa.num_components; i++) { if (alu->src[src_idx].swizzle[i] != i) return false; } return true; } 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_if_branch && !var->in_nested_loop && var->type != invariant); /* We are only interested in checking phis 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_loop_variable *alu_src_var = NULL; 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 an if branch or nested loop then don't * attempt to go any further. */ if (src_var->in_if_branch || src_var->in_nested_loop) break; /* Detect inductions variables that are incremented in both branches * of an unnested if rather than in a loop block. */ if (is_var_phi(src_var)) { nir_phi_instr *src_phi = nir_instr_as_phi(src_var->def->parent_instr); nir_alu_instr *src_phi_alu = phi_instr_as_alu(src_phi); if (src_phi_alu) { src_var = get_loop_var(&src_phi_alu->dest.dest.ssa, state); if (!src_var->in_if_branch) break; } } if (!src_var->in_loop && !biv->def_outside_loop) { biv->def_outside_loop = src_var->def; } else if (is_var_alu(src_var) && !biv->alu) { alu_src_var = src_var; nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr); if (nir_op_infos[alu->op].num_inputs == 2) { for (unsigned i = 0; i < 2; i++) { /* Is one of the operands const, and the other the phi. The * phi source can't be swizzled in any way. */ if (nir_src_is_const(alu->src[i].src) && alu->src[1-i].src.ssa == &phi->dest.ssa && alu_src_has_identity_swizzle(alu, 1 - i)) biv->alu = alu; } } if (!biv->alu) break; } else { biv->alu = NULL; break; } } if (biv->alu && biv->def_outside_loop && biv->def_outside_loop->parent_instr->type == nir_instr_type_load_const) { alu_src_var->type = basic_induction; alu_src_var->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 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 (nir_block_ends_in_break(last_then)) { break_blk = last_then; continue_from_blk = last_else; continue_from_then = false; } else if (nir_block_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)) { state->loop->info->complex_loop = true; 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) { state->loop->info->complex_loop = true; return false; } nir_loop_terminator *terminator = rzalloc(state->loop->info, nir_loop_terminator); list_addtail(&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; } /* This function looks for an array access within a loop that uses an * induction variable for the array index. If found it returns the size of the * array, otherwise 0 is returned. If we find an induction var we pass it back * to the caller via array_index_out. */ static unsigned find_array_access_via_induction(loop_info_state *state, nir_deref_instr *deref, nir_loop_variable **array_index_out) { for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) { if (d->deref_type != nir_deref_type_array) continue; assert(d->arr.index.is_ssa); nir_loop_variable *array_index = get_loop_var(d->arr.index.ssa, state); if (array_index->type != basic_induction) continue; if (array_index_out) *array_index_out = array_index; nir_deref_instr *parent = nir_deref_instr_parent(d); if (glsl_type_is_array_or_matrix(parent->type)) { return glsl_get_length(parent->type); } else { assert(glsl_type_is_vector(parent->type)); return glsl_get_vector_elements(parent->type); } } return 0; } static bool guess_loop_limit(loop_info_state *state, nir_const_value *limit_val, nir_ssa_scalar basic_ind) { unsigned min_array_size = 0; nir_foreach_block_in_cf_node(block, &state->loop->cf_node) { 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. */ if (intrin->intrinsic == nir_intrinsic_load_deref || intrin->intrinsic == nir_intrinsic_store_deref || intrin->intrinsic == nir_intrinsic_copy_deref) { nir_loop_variable *array_idx = NULL; unsigned array_size = find_array_access_via_induction(state, nir_src_as_deref(intrin->src[0]), &array_idx); if (array_idx && basic_ind.def == array_idx->def && (min_array_size == 0 || min_array_size > array_size)) { /* Array indices are scalars */ assert(basic_ind.def->num_components == 1); min_array_size = array_size; } if (intrin->intrinsic != nir_intrinsic_copy_deref) continue; array_size = find_array_access_via_induction(state, nir_src_as_deref(intrin->src[1]), &array_idx); if (array_idx && basic_ind.def == array_idx->def && (min_array_size == 0 || min_array_size > array_size)) { /* Array indices are scalars */ assert(basic_ind.def->num_components == 1); min_array_size = array_size; } } } } if (min_array_size) { *limit_val = nir_const_value_for_uint(min_array_size, basic_ind.def->bit_size); return true; } return false; } static bool try_find_limit_of_alu(nir_ssa_scalar limit, nir_const_value *limit_val, nir_loop_terminator *terminator, loop_info_state *state) { if (!nir_ssa_scalar_is_alu(limit)) return false; nir_op limit_op = nir_ssa_scalar_alu_op(limit); if (limit_op == nir_op_imin || limit_op == nir_op_fmin) { for (unsigned i = 0; i < 2; i++) { nir_ssa_scalar src = nir_ssa_scalar_chase_alu_src(limit, i); if (nir_ssa_scalar_is_const(src)) { *limit_val = nir_ssa_scalar_as_const_value(src); terminator->exact_trip_count_unknown = true; return true; } } } return false; } static nir_const_value eval_const_unop(nir_op op, unsigned bit_size, nir_const_value src0) { assert(nir_op_infos[op].num_inputs == 1); nir_const_value dest; nir_const_value *src[1] = { &src0 }; nir_eval_const_opcode(op, &dest, 1, bit_size, src); return dest; } static nir_const_value eval_const_binop(nir_op op, unsigned bit_size, nir_const_value src0, nir_const_value src1) { assert(nir_op_infos[op].num_inputs == 2); nir_const_value dest; nir_const_value *src[2] = { &src0, &src1 }; nir_eval_const_opcode(op, &dest, 1, bit_size, src); return dest; } static int32_t get_iteration(nir_op cond_op, nir_const_value initial, nir_const_value step, nir_const_value limit, unsigned bit_size) { nir_const_value span, iter; switch (cond_op) { case nir_op_ige: case nir_op_ilt: case nir_op_ieq: case nir_op_ine: span = eval_const_binop(nir_op_isub, bit_size, limit, initial); iter = eval_const_binop(nir_op_idiv, bit_size, span, step); break; case nir_op_uge: case nir_op_ult: span = eval_const_binop(nir_op_isub, bit_size, limit, initial); iter = eval_const_binop(nir_op_udiv, bit_size, span, step); break; case nir_op_fge: case nir_op_flt: case nir_op_feq: case nir_op_fne: span = eval_const_binop(nir_op_fsub, bit_size, limit, initial); iter = eval_const_binop(nir_op_fdiv, bit_size, span, step); iter = eval_const_unop(nir_op_f2i64, bit_size, iter); break; default: return -1; } uint64_t iter_u64 = nir_const_value_as_uint(iter, bit_size); return iter_u64 > INT_MAX ? -1 : (int)iter_u64; } 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; nir_op mul_op; nir_op add_op; switch (induction_base_type) { case nir_type_float: iter_src = nir_const_value_for_float(iter_int, bit_size); mul_op = nir_op_fmul; add_op = nir_op_fadd; break; case nir_type_int: case nir_type_uint: iter_src = nir_const_value_for_int(iter_int, bit_size); 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, &mul_result, 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, &add_result, 1, bit_size, add_src); nir_const_value *src[2]; 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, &result, 1, bit_size, src); return invert_cond ? !result.b : result.b; } static int calculate_iterations(nir_const_value *initial, nir_const_value *step, nir_const_value *limit, nir_alu_instr *alu, nir_ssa_scalar cond, nir_op alu_op, bool limit_rhs, bool invert_cond) { assert(initial != NULL && step != NULL && limit != NULL); /* 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[alu_op].input_types[1]) == nir_type_int || nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[1]) == nir_type_uint); } else { assert(nir_alu_type_get_base_type(nir_op_infos[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; nir_alu_instr *cond_alu = nir_instr_as_alu(cond.def->parent_instr); if (cond_alu->src[0].src.ssa == &alu->dest.dest.ssa || cond_alu->src[1].src.ssa == &alu->dest.dest.ssa) { trip_offset = 1; } 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); int iter_int = get_iteration(alu_op, *initial, *step, *limit, bit_size); /* 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); */ for (int bias = -1; bias <= 1; bias++) { const int iter_bias = iter_int + bias; if (test_iterations(iter_bias, step, limit, alu_op, bit_size, induction_base_type, initial, limit_rhs, invert_cond)) { return iter_bias > 0 ? iter_bias - trip_offset : iter_bias; } } return -1; } static nir_op inverse_comparison(nir_op alu_op) { switch (alu_op) { case nir_op_fge: return nir_op_flt; case nir_op_ige: return nir_op_ilt; case nir_op_uge: return nir_op_ult; case nir_op_flt: return nir_op_fge; case nir_op_ilt: return nir_op_ige; case nir_op_ult: return nir_op_uge; case nir_op_feq: return nir_op_fne; case nir_op_ieq: return nir_op_ine; case nir_op_fne: return nir_op_feq; case nir_op_ine: return nir_op_ieq; default: unreachable("Unsuported comparison!"); } } static bool is_supported_terminator_condition(nir_ssa_scalar cond) { if (!nir_ssa_scalar_is_alu(cond)) return false; nir_alu_instr *alu = nir_instr_as_alu(cond.def->parent_instr); return nir_alu_instr_is_comparison(alu) && nir_op_infos[alu->op].num_inputs == 2; } static bool get_induction_and_limit_vars(nir_ssa_scalar cond, nir_ssa_scalar *ind, nir_ssa_scalar *limit, bool *limit_rhs, loop_info_state *state) { nir_ssa_scalar rhs, lhs; lhs = nir_ssa_scalar_chase_alu_src(cond, 0); rhs = nir_ssa_scalar_chase_alu_src(cond, 1); if (get_loop_var(lhs.def, state)->type == basic_induction) { *ind = lhs; *limit = rhs; *limit_rhs = true; return true; } else if (get_loop_var(rhs.def, state)->type == basic_induction) { *ind = rhs; *limit = lhs; *limit_rhs = false; return true; } else { return false; } } static bool try_find_trip_count_vars_in_iand(nir_ssa_scalar *cond, nir_ssa_scalar *ind, nir_ssa_scalar *limit, bool *limit_rhs, loop_info_state *state) { const nir_op alu_op = nir_ssa_scalar_alu_op(*cond); assert(alu_op == nir_op_ieq || alu_op == nir_op_inot); nir_ssa_scalar iand = nir_ssa_scalar_chase_alu_src(*cond, 0); if (alu_op == nir_op_ieq) { nir_ssa_scalar zero = nir_ssa_scalar_chase_alu_src(*cond, 1); if (!nir_ssa_scalar_is_alu(iand) || !nir_ssa_scalar_is_const(zero)) { /* Maybe we had it the wrong way, flip things around */ nir_ssa_scalar tmp = zero; zero = iand; iand = tmp; /* If we still didn't find what we need then return */ if (!nir_ssa_scalar_is_const(zero)) return false; } /* If the loop is not breaking on (x && y) == 0 then return */ if (nir_ssa_scalar_as_uint(zero) != 0) return false; } if (!nir_ssa_scalar_is_alu(iand)) return false; if (nir_ssa_scalar_alu_op(iand) != nir_op_iand) return false; /* Check if iand src is a terminator condition and try get induction var * and trip limit var. */ bool found_induction_var = false; for (unsigned i = 0; i < 2; i++) { nir_ssa_scalar src = nir_ssa_scalar_chase_alu_src(iand, i); if (is_supported_terminator_condition(src) && get_induction_and_limit_vars(src, ind, limit, limit_rhs, state)) { *cond = src; found_induction_var = true; /* If we've found one with a constant limit, stop. */ if (nir_ssa_scalar_is_const(*limit)) return true; } } return found_induction_var; } /* 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; bool guessed_trip_count = false; nir_loop_terminator *limiting_terminator = NULL; int max_trip_count = -1; list_for_each_entry(nir_loop_terminator, terminator, &state->loop->info->loop_terminator_list, loop_terminator_link) { assert(terminator->nif->condition.is_ssa); nir_ssa_scalar cond = { terminator->nif->condition.ssa, 0 }; if (!nir_ssa_scalar_is_alu(cond)) { /* 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_op alu_op = nir_ssa_scalar_alu_op(cond); bool limit_rhs; nir_ssa_scalar basic_ind = { NULL, 0 }; nir_ssa_scalar limit; if ((alu_op == nir_op_inot || alu_op == nir_op_ieq) && try_find_trip_count_vars_in_iand(&cond, &basic_ind, &limit, &limit_rhs, state)) { /* The loop is exiting on (x && y) == 0 so we need to get the * inverse of x or y (i.e. which ever contained the induction var) in * order to compute the trip count. */ alu_op = inverse_comparison(nir_ssa_scalar_alu_op(cond)); trip_count_known = false; terminator->exact_trip_count_unknown = true; } if (!basic_ind.def) { if (is_supported_terminator_condition(cond)) { get_induction_and_limit_vars(cond, &basic_ind, &limit, &limit_rhs, state); } } /* The comparison has to have a basic induction variable for us to be * able to find trip counts. */ if (!basic_ind.def) { trip_count_known = false; continue; } terminator->induction_rhs = !limit_rhs; /* Attempt to find a constant limit for the loop */ nir_const_value limit_val; if (nir_ssa_scalar_is_const(limit)) { limit_val = nir_ssa_scalar_as_const_value(limit); } else { trip_count_known = false; if (!try_find_limit_of_alu(limit, &limit_val, terminator, state)) { /* Guess loop limit based on array access */ if (!guess_loop_limit(state, &limit_val, basic_ind)) { continue; } guessed_trip_count = true; } } /* 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_basic_induction_var *ind_var = get_loop_var(basic_ind.def, state)->ind; /* The basic induction var might be a vector but, because we guarantee * earlier that the phi source has a scalar swizzle, we can take the * component from basic_ind. */ nir_ssa_scalar initial_s = { ind_var->def_outside_loop, basic_ind.comp }; nir_ssa_scalar alu_s = { &ind_var->alu->dest.dest.ssa, basic_ind.comp }; nir_const_value initial_val = nir_ssa_scalar_as_const_value(initial_s); /* We are guaranteed by earlier code that at least one of these sources * is a constant but we don't know which. */ nir_const_value step_val; memset(&step_val, 0, sizeof(step_val)); UNUSED bool found_step_value = false; assert(nir_op_infos[ind_var->alu->op].num_inputs == 2); for (unsigned i = 0; i < 2; i++) { nir_ssa_scalar alu_src = nir_ssa_scalar_chase_alu_src(alu_s, i); if (nir_ssa_scalar_is_const(alu_src)) { found_step_value = true; step_val = nir_ssa_scalar_as_const_value(alu_src); break; } } assert(found_step_value); int iterations = calculate_iterations(&initial_val, &step_val, &limit_val, ind_var->alu, cond, alu_op, limit_rhs, terminator->continue_from_then); /* Where we not able to calculate the iteration count */ if (iterations == -1) { trip_count_known = false; guessed_trip_count = false; continue; } if (guessed_trip_count) { guessed_trip_count = false; if (state->loop->info->guessed_trip_count == 0 || state->loop->info->guessed_trip_count > iterations) state->loop->info->guessed_trip_count = iterations; 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 (max_trip_count == -1 || iterations < max_trip_count) { max_trip_count = iterations; limiting_terminator = terminator; } } state->loop->info->exact_trip_count_known = trip_count_known; if (max_trip_count > -1) state->loop->info->max_trip_count = max_trip_count; state->loop->info->limiting_terminator = limiting_terminator; } static bool force_unroll_array_access(loop_info_state *state, nir_deref_instr *deref) { unsigned array_size = find_array_access_via_induction(state, deref, NULL); if (array_size) { if (array_size == state->loop->info->max_trip_count) return true; if (deref->mode & state->indirect_mask) return true; } return false; } static bool force_unroll_heuristics(loop_info_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); /* 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_deref || intrin->intrinsic == nir_intrinsic_store_deref || intrin->intrinsic == nir_intrinsic_copy_deref) { if (force_unroll_array_access(state, nir_src_as_deref(intrin->src[0]))) return true; if (intrin->intrinsic == nir_intrinsic_copy_deref && force_unroll_array_access(state, nir_src_as_deref(intrin->src[1]))) return true; } } return false; } static void get_loop_info(loop_info_state *state, nir_function_impl *impl) { nir_shader *shader = impl->function->shader; const nir_shader_compiler_options *options = shader->options; /* Initialize all variables to "outside_loop". This also marks defs * invariant and constant if they are nir_instr_type_load_consts */ 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, false, options); break; case nir_cf_node_if: nir_foreach_block_in_cf_node(block, node) init_loop_block(block, state, true, false, options); break; case nir_cf_node_loop: nir_foreach_block_in_cf_node(block, node) { init_loop_block(block, state, false, true, options); } break; case nir_cf_node_function: break; } } /* 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; } /* 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; /* Run through each of the terminators and try to compute a trip-count */ find_trip_count(state); nir_foreach_block_in_cf_node(block, &state->loop->cf_node) { if (force_unroll_heuristics(state, block)) { state->loop->info->force_unroll = true; 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); }