/* * 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/nir_builder.h" #include "nir_constant_expressions.h" #include "nir_control_flow.h" #include "nir_loop_analyze.h" static nir_ssa_def *clone_alu_and_replace_src_defs(nir_builder *b, const nir_alu_instr *alu, nir_ssa_def **src_defs); /** * Gets the single block that jumps back to the loop header. Already assumes * there is exactly one such block. */ static nir_block* find_continue_block(nir_loop *loop) { nir_block *header_block = nir_loop_first_block(loop); nir_block *prev_block = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node)); assert(header_block->predecessors->entries == 2); set_foreach(header_block->predecessors, pred_entry) { if (pred_entry->key != prev_block) return (nir_block*)pred_entry->key; } unreachable("Continue block not found!"); } /** * Does a phi have one constant value from outside a loop and one from inside? */ static bool phi_has_constant_from_outside_and_one_from_inside_loop(nir_phi_instr *phi, const nir_block *entry_block, bool *entry_val, bool *continue_val) { /* We already know we have exactly one continue */ assert(exec_list_length(&phi->srcs) == 2); *entry_val = false; *continue_val = false; nir_foreach_phi_src(src, phi) { if (!nir_src_is_const(src->src)) return false; if (src->pred != entry_block) { *continue_val = nir_src_as_bool(src->src); } else { *entry_val = nir_src_as_bool(src->src); } } return true; } /** * This optimization detects if statements at the tops of loops where the * condition is a phi node of two constants and moves half of the if to above * the loop and the other half of the if to the end of the loop. A simple for * loop "for (int i = 0; i < 4; i++)", when run through the SPIR-V front-end, * ends up looking something like this: * * vec1 32 ssa_0 = load_const (0x00000000) * vec1 32 ssa_1 = load_const (0xffffffff) * loop { * block block_1: * vec1 32 ssa_2 = phi block_0: ssa_0, block_7: ssa_5 * vec1 32 ssa_3 = phi block_0: ssa_0, block_7: ssa_1 * if ssa_3 { * block block_2: * vec1 32 ssa_4 = load_const (0x00000001) * vec1 32 ssa_5 = iadd ssa_2, ssa_4 * } else { * block block_3: * } * block block_4: * vec1 32 ssa_6 = load_const (0x00000004) * vec1 32 ssa_7 = ilt ssa_5, ssa_6 * if ssa_7 { * block block_5: * } else { * block block_6: * break * } * block block_7: * } * * This turns it into something like this: * * // Stuff from block 1 * // Stuff from block 3 * loop { * block block_1: * vec1 32 ssa_2 = phi block_0: ssa_0, block_7: ssa_5 * vec1 32 ssa_6 = load_const (0x00000004) * vec1 32 ssa_7 = ilt ssa_2, ssa_6 * if ssa_7 { * block block_5: * } else { * block block_6: * break * } * block block_7: * // Stuff from block 1 * // Stuff from block 2 * vec1 32 ssa_4 = load_const (0x00000001) * vec1 32 ssa_5 = iadd ssa_2, ssa_4 * } */ static bool opt_peel_loop_initial_if(nir_loop *loop) { nir_block *header_block = nir_loop_first_block(loop); nir_block *const prev_block = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node)); /* It would be insane if this were not true */ assert(_mesa_set_search(header_block->predecessors, prev_block)); /* The loop must have exactly one continue block which could be a block * ending in a continue instruction or the "natural" continue from the * last block in the loop back to the top. */ if (header_block->predecessors->entries != 2) return false; nir_cf_node *if_node = nir_cf_node_next(&header_block->cf_node); if (!if_node || if_node->type != nir_cf_node_if) return false; nir_if *nif = nir_cf_node_as_if(if_node); assert(nif->condition.is_ssa); nir_ssa_def *cond = nif->condition.ssa; if (cond->parent_instr->type != nir_instr_type_phi) return false; nir_phi_instr *cond_phi = nir_instr_as_phi(cond->parent_instr); if (cond->parent_instr->block != header_block) return false; bool entry_val = false, continue_val = false; if (!phi_has_constant_from_outside_and_one_from_inside_loop(cond_phi, prev_block, &entry_val, &continue_val)) return false; /* If they both execute or both don't execute, this is a job for * nir_dead_cf, not this pass. */ if ((entry_val && continue_val) || (!entry_val && !continue_val)) return false; struct exec_list *continue_list, *entry_list; if (continue_val) { continue_list = &nif->then_list; entry_list = &nif->else_list; } else { continue_list = &nif->else_list; entry_list = &nif->then_list; } /* We want to be moving the contents of entry_list to above the loop so it * can't contain any break or continue instructions. */ foreach_list_typed(nir_cf_node, cf_node, node, entry_list) { nir_foreach_block_in_cf_node(block, cf_node) { nir_instr *last_instr = nir_block_last_instr(block); if (last_instr && last_instr->type == nir_instr_type_jump) return false; } } /* We're about to re-arrange a bunch of blocks so make sure that we don't * have deref uses which cross block boundaries. We don't want a deref * accidentally ending up in a phi. */ nir_rematerialize_derefs_in_use_blocks_impl( nir_cf_node_get_function(&loop->cf_node)); /* Before we do anything, convert the loop to LCSSA. We're about to * replace a bunch of SSA defs with registers and this will prevent any of * it from leaking outside the loop. */ nir_convert_loop_to_lcssa(loop); nir_block *after_if_block = nir_cf_node_as_block(nir_cf_node_next(&nif->cf_node)); /* Get rid of phis in the header block since we will be duplicating it */ nir_lower_phis_to_regs_block(header_block); /* Get rid of phis after the if since dominance will change */ nir_lower_phis_to_regs_block(after_if_block); /* Get rid of SSA defs in the pieces we're about to move around */ nir_lower_ssa_defs_to_regs_block(header_block); nir_foreach_block_in_cf_node(block, &nif->cf_node) nir_lower_ssa_defs_to_regs_block(block); nir_cf_list header, tmp; nir_cf_extract(&header, nir_before_block(header_block), nir_after_block(header_block)); nir_cf_list_clone(&tmp, &header, &loop->cf_node, NULL); nir_cf_reinsert(&tmp, nir_before_cf_node(&loop->cf_node)); nir_cf_extract(&tmp, nir_before_cf_list(entry_list), nir_after_cf_list(entry_list)); nir_cf_reinsert(&tmp, nir_before_cf_node(&loop->cf_node)); nir_cf_reinsert(&header, nir_after_block_before_jump(find_continue_block(loop))); bool continue_list_jumps = nir_block_ends_in_jump(exec_node_data(nir_block, exec_list_get_tail(continue_list), cf_node.node)); nir_cf_extract(&tmp, nir_before_cf_list(continue_list), nir_after_cf_list(continue_list)); /* Get continue block again as the previous reinsert might have removed the * block. Also, if both the continue list and the continue block ends in * jump instructions, removes the jump from the latter, as it will not be * executed if we insert the continue list before it. */ nir_block *continue_block = find_continue_block(loop); if (continue_list_jumps) { nir_instr *last_instr = nir_block_last_instr(continue_block); if (last_instr && last_instr->type == nir_instr_type_jump) nir_instr_remove(last_instr); } nir_cf_reinsert(&tmp, nir_after_block_before_jump(continue_block)); nir_cf_node_remove(&nif->cf_node); return true; } static bool alu_instr_is_comparison(const nir_alu_instr *alu) { switch (alu->op) { case nir_op_flt32: case nir_op_fge32: case nir_op_feq32: case nir_op_fneu32: case nir_op_ilt32: case nir_op_ult32: case nir_op_ige32: case nir_op_uge32: case nir_op_ieq32: case nir_op_ine32: return true; default: return nir_alu_instr_is_comparison(alu); } } static bool alu_instr_is_type_conversion(const nir_alu_instr *alu) { return nir_op_infos[alu->op].num_inputs == 1 && nir_op_infos[alu->op].output_type != nir_op_infos[alu->op].input_types[0]; } static bool is_trivial_bcsel(const nir_instr *instr, bool allow_non_phi_src) { if (instr->type != nir_instr_type_alu) return false; nir_alu_instr *const bcsel = nir_instr_as_alu(instr); if (bcsel->op != nir_op_bcsel && bcsel->op != nir_op_b32csel && bcsel->op != nir_op_fcsel) return false; for (unsigned i = 0; i < 3; i++) { if (!nir_alu_src_is_trivial_ssa(bcsel, i) || bcsel->src[i].src.ssa->parent_instr->block != instr->block) return false; if (bcsel->src[i].src.ssa->parent_instr->type != nir_instr_type_phi) { /* opt_split_alu_of_phi() is able to peel that src from the loop */ if (i == 0 || !allow_non_phi_src) return false; allow_non_phi_src = false; } } nir_foreach_phi_src(src, nir_instr_as_phi(bcsel->src[0].src.ssa->parent_instr)) { if (!nir_src_is_const(src->src)) return false; } return true; } /** * Splits ALU instructions that have a source that is a phi node * * ALU instructions in the header block of a loop that meet the following * criteria can be split. * * - The loop has no continue instructions other than the "natural" continue * at the bottom of the loop. * * - At least one source of the instruction is a phi node from the header block. * * - Any non-phi sources of the ALU instruction come from a block that * dominates the block before the loop. The most common failure mode for * this check is sources that are generated in the loop header block. * * - The phi node selects a constant or undef from the block before the loop or * the only ALU user is a trivial bcsel that gets removed by peeling the ALU * * The split process splits the original ALU instruction into two, one at the * bottom of the loop and one at the block before the loop. The instruction * before the loop computes the value on the first iteration, and the * instruction at the bottom computes the value on the second, third, and so * on. A new phi node is added to the header block that selects either the * instruction before the loop or the one at the end, and uses of the original * instruction are replaced by this phi. * * The splitting transforms a loop like: * * vec1 32 ssa_8 = load_const (0x00000001) * vec1 32 ssa_10 = load_const (0x00000000) * // succs: block_1 * loop { * block block_1: * // preds: block_0 block_4 * vec1 32 ssa_11 = phi block_0: ssa_10, block_4: ssa_15 * vec1 32 ssa_12 = phi block_0: ssa_1, block_4: ssa_15 * vec1 32 ssa_13 = phi block_0: ssa_10, block_4: ssa_16 * vec1 32 ssa_14 = iadd ssa_11, ssa_8 * vec1 32 ssa_15 = b32csel ssa_13, ssa_14, ssa_12 * ... * // succs: block_1 * } * * into: * * vec1 32 ssa_8 = load_const (0x00000001) * vec1 32 ssa_10 = load_const (0x00000000) * vec1 32 ssa_22 = iadd ssa_10, ssa_8 * // succs: block_1 * loop { * block block_1: * // preds: block_0 block_4 * vec1 32 ssa_11 = phi block_0: ssa_10, block_4: ssa_15 * vec1 32 ssa_12 = phi block_0: ssa_1, block_4: ssa_15 * vec1 32 ssa_13 = phi block_0: ssa_10, block_4: ssa_16 * vec1 32 ssa_21 = phi block_0: ssa_22, block_4: ssa_20 * vec1 32 ssa_15 = b32csel ssa_13, ssa_21, ssa_12 * ... * vec1 32 ssa_20 = iadd ssa_15, ssa_8 * // succs: block_1 * } */ static bool opt_split_alu_of_phi(nir_builder *b, nir_loop *loop) { bool progress = false; nir_block *header_block = nir_loop_first_block(loop); nir_block *const prev_block = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node)); /* It would be insane if this were not true */ assert(_mesa_set_search(header_block->predecessors, prev_block)); /* The loop must have exactly one continue block which could be a block * ending in a continue instruction or the "natural" continue from the * last block in the loop back to the top. */ if (header_block->predecessors->entries != 2) return false; nir_foreach_instr_safe(instr, header_block) { if (instr->type != nir_instr_type_alu) continue; nir_alu_instr *const alu = nir_instr_as_alu(instr); /* nir_op_vec{2,3,4} and nir_op_mov are excluded because they can easily * lead to infinite optimization loops. Splitting comparisons can lead * to loop unrolling not recognizing loop termintators, and type * conversions also lead to regressions. */ if (nir_op_is_vec(alu->op) || alu_instr_is_comparison(alu) || alu_instr_is_type_conversion(alu)) continue; bool has_phi_src_from_prev_block = false; bool all_non_phi_exist_in_prev_block = true; bool is_prev_result_undef = true; bool is_prev_result_const = true; nir_ssa_def *prev_srcs[8]; // FINISHME: Array size? nir_ssa_def *continue_srcs[8]; // FINISHME: Array size? for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) { nir_instr *const src_instr = alu->src[i].src.ssa->parent_instr; /* If the source is a phi in the loop header block, then the * prev_srcs and continue_srcs will come from the different sources * of the phi. */ if (src_instr->type == nir_instr_type_phi && src_instr->block == header_block) { nir_phi_instr *const phi = nir_instr_as_phi(src_instr); /* Only strictly need to NULL out the pointers when the assertions * (below) are compiled in. Debugging a NULL pointer deref in the * wild is easier than debugging a random pointer deref, so set * NULL unconditionally just to be safe. */ prev_srcs[i] = NULL; continue_srcs[i] = NULL; nir_foreach_phi_src(src_of_phi, phi) { if (src_of_phi->pred == prev_block) { if (src_of_phi->src.ssa->parent_instr->type != nir_instr_type_ssa_undef) { is_prev_result_undef = false; } if (src_of_phi->src.ssa->parent_instr->type != nir_instr_type_load_const) { is_prev_result_const = false; } prev_srcs[i] = src_of_phi->src.ssa; has_phi_src_from_prev_block = true; } else continue_srcs[i] = src_of_phi->src.ssa; } assert(prev_srcs[i] != NULL); assert(continue_srcs[i] != NULL); } else { /* If the source is not a phi (or a phi in a block other than the * loop header), then the value must exist in prev_block. */ if (!nir_block_dominates(src_instr->block, prev_block)) { all_non_phi_exist_in_prev_block = false; break; } prev_srcs[i] = alu->src[i].src.ssa; continue_srcs[i] = alu->src[i].src.ssa; } } if (!has_phi_src_from_prev_block || !all_non_phi_exist_in_prev_block) continue; if (!is_prev_result_undef && !is_prev_result_const) { /* check if the only user is a trivial bcsel */ if (!list_is_empty(&alu->dest.dest.ssa.if_uses) || !list_is_singular(&alu->dest.dest.ssa.uses)) continue; nir_src *use = list_first_entry(&alu->dest.dest.ssa.uses, nir_src, use_link); if (!is_trivial_bcsel(use->parent_instr, true)) continue; } /* Split ALU of Phi */ nir_block *const continue_block = find_continue_block(loop); b->cursor = nir_after_block(prev_block); nir_ssa_def *prev_value = clone_alu_and_replace_src_defs(b, alu, prev_srcs); /* Make a copy of the original ALU instruction. Replace the sources * of the new instruction that read a phi with an undef source from * prev_block with the non-undef source of that phi. * * Insert the new instruction at the end of the continue block. */ b->cursor = nir_after_block_before_jump(continue_block); nir_ssa_def *const alu_copy = clone_alu_and_replace_src_defs(b, alu, continue_srcs); /* Make a new phi node that selects a value from prev_block and the * result of the new instruction from continue_block. */ nir_phi_instr *const phi = nir_phi_instr_create(b->shader); nir_phi_src *phi_src; phi_src = ralloc(phi, nir_phi_src); phi_src->pred = prev_block; phi_src->src = nir_src_for_ssa(prev_value); exec_list_push_tail(&phi->srcs, &phi_src->node); phi_src = ralloc(phi, nir_phi_src); phi_src->pred = continue_block; phi_src->src = nir_src_for_ssa(alu_copy); exec_list_push_tail(&phi->srcs, &phi_src->node); nir_ssa_dest_init(&phi->instr, &phi->dest, alu_copy->num_components, alu_copy->bit_size, NULL); b->cursor = nir_after_phis(header_block); nir_builder_instr_insert(b, &phi->instr); /* Modify all readers of the original ALU instruction to read the * result of the phi. */ nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(&phi->dest.ssa)); /* Since the original ALU instruction no longer has any readers, just * remove it. */ nir_instr_remove_v(&alu->instr); ralloc_free(alu); progress = true; } return progress; } /** * Get the SSA value from a phi node that corresponds to a specific block */ static nir_ssa_def * ssa_for_phi_from_block(nir_phi_instr *phi, nir_block *block) { nir_foreach_phi_src(src, phi) { if (src->pred == block) return src->src.ssa; } assert(!"Block is not a predecessor of phi."); return NULL; } /** * Simplify a bcsel whose sources are all phi nodes from the loop header block * * bcsel instructions in a loop that meet the following criteria can be * converted to phi nodes: * * - The loop has no continue instructions other than the "natural" continue * at the bottom of the loop. * * - All of the sources of the bcsel are phi nodes in the header block of the * loop. * * - The phi node representing the condition of the bcsel instruction chooses * only constant values. * * The contant value from the condition will select one of the other sources * when entered from outside the loop and the remaining source when entered * from the continue block. Since each of these sources is also a phi node in * the header block, the value of the phi node can be "evaluated." These * evaluated phi nodes provide the sources for a new phi node. All users of * the bcsel result are updated to use the phi node result. * * The replacement transforms loops like: * * vec1 32 ssa_7 = undefined * vec1 32 ssa_8 = load_const (0x00000001) * vec1 32 ssa_9 = load_const (0x000000c8) * vec1 32 ssa_10 = load_const (0x00000000) * // succs: block_1 * loop { * block block_1: * // preds: block_0 block_4 * vec1 32 ssa_11 = phi block_0: ssa_1, block_4: ssa_14 * vec1 32 ssa_12 = phi block_0: ssa_10, block_4: ssa_15 * vec1 32 ssa_13 = phi block_0: ssa_7, block_4: ssa_25 * vec1 32 ssa_14 = b32csel ssa_12, ssa_13, ssa_11 * vec1 32 ssa_16 = ige32 ssa_14, ssa_9 * ... * vec1 32 ssa_15 = load_const (0xffffffff) * ... * vec1 32 ssa_25 = iadd ssa_14, ssa_8 * // succs: block_1 * } * * into: * * vec1 32 ssa_7 = undefined * vec1 32 ssa_8 = load_const (0x00000001) * vec1 32 ssa_9 = load_const (0x000000c8) * vec1 32 ssa_10 = load_const (0x00000000) * // succs: block_1 * loop { * block block_1: * // preds: block_0 block_4 * vec1 32 ssa_11 = phi block_0: ssa_1, block_4: ssa_14 * vec1 32 ssa_12 = phi block_0: ssa_10, block_4: ssa_15 * vec1 32 ssa_13 = phi block_0: ssa_7, block_4: ssa_25 * vec1 32 sss_26 = phi block_0: ssa_1, block_4: ssa_25 * vec1 32 ssa_16 = ige32 ssa_26, ssa_9 * ... * vec1 32 ssa_15 = load_const (0xffffffff) * ... * vec1 32 ssa_25 = iadd ssa_26, ssa_8 * // succs: block_1 * } * * \note * It may be possible modify this function to not require a phi node as the * source of the bcsel that is selected when entering from outside the loop. * The only restriction is that the source must be geneated outside the loop * (since it will become the source of a phi node in the header block of the * loop). */ static bool opt_simplify_bcsel_of_phi(nir_builder *b, nir_loop *loop) { bool progress = false; nir_block *header_block = nir_loop_first_block(loop); nir_block *const prev_block = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node)); /* It would be insane if this were not true */ assert(_mesa_set_search(header_block->predecessors, prev_block)); /* The loop must have exactly one continue block which could be a block * ending in a continue instruction or the "natural" continue from the * last block in the loop back to the top. */ if (header_block->predecessors->entries != 2) return false; /* We can move any bcsel that can guaranteed to execut on every iteration * of a loop. For now this is accomplished by only taking bcsels from the * header_block. In the future, this could be expanced to include any * bcsel that must come before any break. * * For more details, see * https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/170#note_110305 */ nir_foreach_instr_safe(instr, header_block) { if (!is_trivial_bcsel(instr, false)) continue; nir_alu_instr *const bcsel = nir_instr_as_alu(instr); nir_phi_instr *const cond_phi = nir_instr_as_phi(bcsel->src[0].src.ssa->parent_instr); bool entry_val = false, continue_val = false; if (!phi_has_constant_from_outside_and_one_from_inside_loop(cond_phi, prev_block, &entry_val, &continue_val)) continue; /* If they both execute or both don't execute, this is a job for * nir_dead_cf, not this pass. */ if ((entry_val && continue_val) || (!entry_val && !continue_val)) continue; const unsigned entry_src = entry_val ? 1 : 2; const unsigned continue_src = entry_val ? 2 : 1; /* Create a new phi node that selects the value for prev_block from * the bcsel source that is selected by entry_val and the value for * continue_block from the other bcsel source. Both sources have * already been verified to be phi nodes. */ nir_block *const continue_block = find_continue_block(loop); nir_phi_instr *const phi = nir_phi_instr_create(b->shader); nir_phi_src *phi_src; phi_src = ralloc(phi, nir_phi_src); phi_src->pred = prev_block; phi_src->src = nir_src_for_ssa(ssa_for_phi_from_block(nir_instr_as_phi(bcsel->src[entry_src].src.ssa->parent_instr), prev_block)); exec_list_push_tail(&phi->srcs, &phi_src->node); phi_src = ralloc(phi, nir_phi_src); phi_src->pred = continue_block; phi_src->src = nir_src_for_ssa(ssa_for_phi_from_block(nir_instr_as_phi(bcsel->src[continue_src].src.ssa->parent_instr), continue_block)); exec_list_push_tail(&phi->srcs, &phi_src->node); nir_ssa_dest_init(&phi->instr, &phi->dest, nir_dest_num_components(bcsel->dest.dest), nir_dest_bit_size(bcsel->dest.dest), NULL); b->cursor = nir_after_phis(header_block); nir_builder_instr_insert(b, &phi->instr); /* Modify all readers of the bcsel instruction to read the result of * the phi. */ nir_ssa_def_rewrite_uses(&bcsel->dest.dest.ssa, nir_src_for_ssa(&phi->dest.ssa)); /* Since the original bcsel instruction no longer has any readers, * just remove it. */ nir_instr_remove_v(&bcsel->instr); ralloc_free(bcsel); progress = true; } return progress; } static bool is_block_empty(nir_block *block) { return nir_cf_node_is_last(&block->cf_node) && exec_list_is_empty(&block->instr_list); } static bool nir_block_ends_in_continue(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_continue; } /** * This optimization turns: * * loop { * ... * if (cond) { * do_work_1(); * continue; * } else { * } * do_work_2(); * } * * into: * * loop { * ... * if (cond) { * do_work_1(); * continue; * } else { * do_work_2(); * } * } * * The continue should then be removed by nir_opt_trivial_continues() and the * loop can potentially be unrolled. * * Note: Unless the function param aggressive_last_continue==true do_work_2() * is only ever blocks and nested loops. We avoid nesting other if-statments * in the branch as this can result in increased register pressure, and in * the i965 driver it causes a large amount of spilling in shader-db. * For RADV however nesting these if-statements allows further continues to be * remove and provides a significant FPS boost in Doom, which is why we have * opted for this special bool to enable more aggresive optimisations. * TODO: The GCM pass solves most of the spilling regressions in i965, if it * is ever enabled we should consider removing the aggressive_last_continue * param. */ static bool opt_if_loop_last_continue(nir_loop *loop, bool aggressive_last_continue) { nir_if *nif; bool then_ends_in_continue = false; bool else_ends_in_continue = false; /* Scan the control flow of the loop from the last to the first node * looking for an if-statement we can optimise. */ nir_block *last_block = nir_loop_last_block(loop); nir_cf_node *if_node = nir_cf_node_prev(&last_block->cf_node); while (if_node) { if (if_node->type == nir_cf_node_if) { nif = nir_cf_node_as_if(if_node); nir_block *then_block = nir_if_last_then_block(nif); nir_block *else_block = nir_if_last_else_block(nif); then_ends_in_continue = nir_block_ends_in_continue(then_block); else_ends_in_continue = nir_block_ends_in_continue(else_block); /* If both branches end in a jump do nothing, this should be handled * by nir_opt_dead_cf(). */ if ((then_ends_in_continue || nir_block_ends_in_break(then_block)) && (else_ends_in_continue || nir_block_ends_in_break(else_block))) return false; /* If continue found stop scanning and attempt optimisation, or */ if (then_ends_in_continue || else_ends_in_continue || !aggressive_last_continue) break; } if_node = nir_cf_node_prev(if_node); } /* If we didn't find an if to optimise return */ if (!then_ends_in_continue && !else_ends_in_continue) return false; /* If there is nothing after the if-statement we bail */ if (&nif->cf_node == nir_cf_node_prev(&last_block->cf_node) && exec_list_is_empty(&last_block->instr_list)) return false; /* Move the last block of the loop inside the last if-statement */ nir_cf_list tmp; nir_cf_extract(&tmp, nir_after_cf_node(if_node), nir_after_block(last_block)); if (then_ends_in_continue) nir_cf_reinsert(&tmp, nir_after_cf_list(&nif->else_list)); else nir_cf_reinsert(&tmp, nir_after_cf_list(&nif->then_list)); /* In order to avoid running nir_lower_regs_to_ssa_impl() every time an if * opt makes progress we leave nir_opt_trivial_continues() to remove the * continue now that the end of the loop has been simplified. */ return true; } /* Walk all the phis in the block immediately following the if statement and * swap the blocks. */ static void rewrite_phi_predecessor_blocks(nir_if *nif, nir_block *old_then_block, nir_block *old_else_block, nir_block *new_then_block, nir_block *new_else_block) { nir_block *after_if_block = nir_cf_node_as_block(nir_cf_node_next(&nif->cf_node)); nir_foreach_instr(instr, after_if_block) { if (instr->type != nir_instr_type_phi) continue; nir_phi_instr *phi = nir_instr_as_phi(instr); foreach_list_typed(nir_phi_src, src, node, &phi->srcs) { if (src->pred == old_then_block) { src->pred = new_then_block; } else if (src->pred == old_else_block) { src->pred = new_else_block; } } } } /** * This optimization turns: * * if (cond) { * } else { * do_work(); * } * * into: * * if (!cond) { * do_work(); * } else { * } */ static bool opt_if_simplification(nir_builder *b, nir_if *nif) { /* Only simplify if the then block is empty and the else block is not. */ if (!is_block_empty(nir_if_first_then_block(nif)) || is_block_empty(nir_if_first_else_block(nif))) return false; /* Make sure the condition is a comparison operation. */ nir_instr *src_instr = nif->condition.ssa->parent_instr; if (src_instr->type != nir_instr_type_alu) return false; nir_alu_instr *alu_instr = nir_instr_as_alu(src_instr); if (!nir_alu_instr_is_comparison(alu_instr)) return false; /* Insert the inverted instruction and rewrite the condition. */ b->cursor = nir_after_instr(&alu_instr->instr); nir_ssa_def *new_condition = nir_inot(b, &alu_instr->dest.dest.ssa); nir_if_rewrite_condition(nif, nir_src_for_ssa(new_condition)); /* Grab pointers to the last then/else blocks for fixing up the phis. */ nir_block *then_block = nir_if_last_then_block(nif); nir_block *else_block = nir_if_last_else_block(nif); if (nir_block_ends_in_jump(else_block)) { /* Even though this if statement has a jump on one side, we may still have * phis afterwards. Single-source phis can be produced by loop unrolling * or dead control-flow passes and are perfectly legal. Run a quick phi * removal on the block after the if to clean up any such phis. */ nir_block *const next_block = nir_cf_node_as_block(nir_cf_node_next(&nif->cf_node)); nir_opt_remove_phis_block(next_block); } rewrite_phi_predecessor_blocks(nif, then_block, else_block, else_block, then_block); /* Finally, move the else block to the then block. */ nir_cf_list tmp; nir_cf_extract(&tmp, nir_before_cf_list(&nif->else_list), nir_after_cf_list(&nif->else_list)); nir_cf_reinsert(&tmp, nir_before_cf_list(&nif->then_list)); return true; } /** * This optimization simplifies potential loop terminators which then allows * other passes such as opt_if_simplification() and loop unrolling to progress * further: * * if (cond) { * ... then block instructions ... * } else { * ... * break; * } * * into: * * if (cond) { * } else { * ... * break; * } * ... then block instructions ... */ static bool opt_if_loop_terminator(nir_if *nif) { 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; } /* Continue if the if-statement contained no jumps at all */ if (!break_blk) return false; /* If the continue from block is empty then return as there is nothing to * move. */ nir_block *first_continue_from_blk = continue_from_then ? nir_if_first_then_block(nif) : nir_if_first_else_block(nif); if (is_block_empty(first_continue_from_blk)) return false; if (nir_block_ends_in_jump(continue_from_blk)) return false; /* Even though this if statement has a jump on one side, we may still have * phis afterwards. Single-source phis can be produced by loop unrolling * or dead control-flow passes and are perfectly legal. Run a quick phi * removal on the block after the if to clean up any such phis. */ nir_opt_remove_phis_block(nir_cf_node_as_block(nir_cf_node_next(&nif->cf_node))); /* Finally, move the continue from branch after the if-statement. */ nir_cf_list tmp; nir_cf_extract(&tmp, nir_before_block(first_continue_from_blk), nir_after_block(continue_from_blk)); nir_cf_reinsert(&tmp, nir_after_cf_node(&nif->cf_node)); return true; } static bool evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value) { nir_block *use_block = nir_cursor_current_block(cursor); if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) { *value = true; return true; } else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) { *value = false; return true; } else { return false; } } static nir_ssa_def * clone_alu_and_replace_src_defs(nir_builder *b, const nir_alu_instr *alu, nir_ssa_def **src_defs) { nir_alu_instr *nalu = nir_alu_instr_create(b->shader, alu->op); nalu->exact = alu->exact; nir_ssa_dest_init(&nalu->instr, &nalu->dest.dest, alu->dest.dest.ssa.num_components, alu->dest.dest.ssa.bit_size, alu->dest.dest.ssa.name); nalu->dest.saturate = alu->dest.saturate; nalu->dest.write_mask = alu->dest.write_mask; for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) { assert(alu->src[i].src.is_ssa); nalu->src[i].src = nir_src_for_ssa(src_defs[i]); nalu->src[i].negate = alu->src[i].negate; nalu->src[i].abs = alu->src[i].abs; memcpy(nalu->src[i].swizzle, alu->src[i].swizzle, sizeof(nalu->src[i].swizzle)); } nir_builder_instr_insert(b, &nalu->instr); return &nalu->dest.dest.ssa;; } /* * This propagates if condition evaluation down the chain of some alu * instructions. For example by checking the use of some of the following alu * instruction we can eventually replace ssa_107 with NIR_TRUE. * * loop { * block block_1: * vec1 32 ssa_85 = load_const (0x00000002) * vec1 32 ssa_86 = ieq ssa_48, ssa_85 * vec1 32 ssa_87 = load_const (0x00000001) * vec1 32 ssa_88 = ieq ssa_48, ssa_87 * vec1 32 ssa_89 = ior ssa_86, ssa_88 * vec1 32 ssa_90 = ieq ssa_48, ssa_0 * vec1 32 ssa_91 = ior ssa_89, ssa_90 * if ssa_86 { * block block_2: * ... * break * } else { * block block_3: * } * block block_4: * if ssa_88 { * block block_5: * ... * break * } else { * block block_6: * } * block block_7: * if ssa_90 { * block block_8: * ... * break * } else { * block block_9: * } * block block_10: * vec1 32 ssa_107 = inot ssa_91 * if ssa_107 { * block block_11: * break * } else { * block block_12: * } * } */ static bool propagate_condition_eval(nir_builder *b, nir_if *nif, nir_src *use_src, nir_src *alu_use, nir_alu_instr *alu, bool is_if_condition) { bool bool_value; b->cursor = nir_before_src(alu_use, is_if_condition); if (!evaluate_if_condition(nif, b->cursor, &bool_value)) return false; nir_ssa_def *def[NIR_MAX_VEC_COMPONENTS] = {0}; for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) { if (alu->src[i].src.ssa == use_src->ssa) { def[i] = nir_imm_bool(b, bool_value); } else { def[i] = alu->src[i].src.ssa; } } nir_ssa_def *nalu = clone_alu_and_replace_src_defs(b, alu, def); /* Rewrite use to use new alu instruction */ nir_src new_src = nir_src_for_ssa(nalu); if (is_if_condition) nir_if_rewrite_condition(alu_use->parent_if, new_src); else nir_instr_rewrite_src(alu_use->parent_instr, alu_use, new_src); return true; } static bool can_propagate_through_alu(nir_src *src) { if (src->parent_instr->type != nir_instr_type_alu) return false; nir_alu_instr *alu = nir_instr_as_alu(src->parent_instr); switch (alu->op) { case nir_op_ior: case nir_op_iand: case nir_op_inot: case nir_op_b2i32: return true; case nir_op_bcsel: return src == &alu->src[0].src; default: return false; } } static bool evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src, bool is_if_condition) { bool progress = false; b->cursor = nir_before_src(use_src, is_if_condition); bool bool_value; if (evaluate_if_condition(nif, b->cursor, &bool_value)) { /* Rewrite use to use const */ nir_src imm_src = nir_src_for_ssa(nir_imm_bool(b, bool_value)); if (is_if_condition) nir_if_rewrite_condition(use_src->parent_if, imm_src); else nir_instr_rewrite_src(use_src->parent_instr, use_src, imm_src); progress = true; } if (!is_if_condition && can_propagate_through_alu(use_src)) { nir_alu_instr *alu = nir_instr_as_alu(use_src->parent_instr); nir_foreach_use_safe(alu_use, &alu->dest.dest.ssa) { progress |= propagate_condition_eval(b, nif, use_src, alu_use, alu, false); } nir_foreach_if_use_safe(alu_use, &alu->dest.dest.ssa) { progress |= propagate_condition_eval(b, nif, use_src, alu_use, alu, true); } } return progress; } static bool opt_if_evaluate_condition_use(nir_builder *b, nir_if *nif) { bool progress = false; /* Evaluate any uses of the if condition inside the if branches */ assert(nif->condition.is_ssa); nir_foreach_use_safe(use_src, nif->condition.ssa) { progress |= evaluate_condition_use(b, nif, use_src, false); } nir_foreach_if_use_safe(use_src, nif->condition.ssa) { if (use_src->parent_if != nif) progress |= evaluate_condition_use(b, nif, use_src, true); } return progress; } static void simple_merge_if(nir_if *dest_if, nir_if *src_if, bool dest_if_then, bool src_if_then) { /* Now merge the if branch */ nir_block *dest_blk = dest_if_then ? nir_if_last_then_block(dest_if) : nir_if_last_else_block(dest_if); struct exec_list *list = src_if_then ? &src_if->then_list : &src_if->else_list; nir_cf_list if_cf_list; nir_cf_extract(&if_cf_list, nir_before_cf_list(list), nir_after_cf_list(list)); nir_cf_reinsert(&if_cf_list, nir_after_block(dest_blk)); } static bool opt_if_merge(nir_if *nif) { bool progress = false; nir_block *next_blk = nir_cf_node_cf_tree_next(&nif->cf_node); if (!next_blk || !nif->condition.is_ssa) return false; nir_if *next_if = nir_block_get_following_if(next_blk); if (!next_if || !next_if->condition.is_ssa) return false; /* Here we merge two consecutive ifs that have the same condition e.g: * * if ssa_12 { * ... * } else { * ... * } * if ssa_12 { * ... * } else { * ... * } * * Note: This only merges if-statements when the block between them is * empty. The reason we don't try to merge ifs that just have phis between * them is because this can result in increased register pressure. For * example when merging if ladders created by indirect indexing. */ if (nif->condition.ssa == next_if->condition.ssa && exec_list_is_empty(&next_blk->instr_list)) { /* This optimization isn't made to work in this case and * opt_if_evaluate_condition_use will optimize it later. */ if (nir_block_ends_in_jump(nir_if_last_then_block(nif)) || nir_block_ends_in_jump(nir_if_last_else_block(nif))) return false; simple_merge_if(nif, next_if, true, true); simple_merge_if(nif, next_if, false, false); nir_block *new_then_block = nir_if_last_then_block(nif); nir_block *new_else_block = nir_if_last_else_block(nif); nir_block *old_then_block = nir_if_last_then_block(next_if); nir_block *old_else_block = nir_if_last_else_block(next_if); /* Rewrite the predecessor block for any phis following the second * if-statement. */ rewrite_phi_predecessor_blocks(next_if, old_then_block, old_else_block, new_then_block, new_else_block); /* Move phis after merged if to avoid them being deleted when we remove * the merged if-statement. */ nir_block *after_next_if_block = nir_cf_node_as_block(nir_cf_node_next(&next_if->cf_node)); nir_foreach_instr_safe(instr, after_next_if_block) { if (instr->type != nir_instr_type_phi) break; exec_node_remove(&instr->node); exec_list_push_tail(&next_blk->instr_list, &instr->node); instr->block = next_blk; } nir_cf_node_remove(&next_if->cf_node); progress = true; } return progress; } static bool opt_if_cf_list(nir_builder *b, struct exec_list *cf_list, bool aggressive_last_continue) { bool progress = false; foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { switch (cf_node->type) { case nir_cf_node_block: break; case nir_cf_node_if: { nir_if *nif = nir_cf_node_as_if(cf_node); progress |= opt_if_cf_list(b, &nif->then_list, aggressive_last_continue); progress |= opt_if_cf_list(b, &nif->else_list, aggressive_last_continue); progress |= opt_if_loop_terminator(nif); progress |= opt_if_merge(nif); progress |= opt_if_simplification(b, nif); break; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(cf_node); progress |= opt_if_cf_list(b, &loop->body, aggressive_last_continue); progress |= opt_simplify_bcsel_of_phi(b, loop); progress |= opt_if_loop_last_continue(loop, aggressive_last_continue); break; } case nir_cf_node_function: unreachable("Invalid cf type"); } } return progress; } static bool opt_peel_loop_initial_if_cf_list(struct exec_list *cf_list) { bool progress = false; foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { switch (cf_node->type) { case nir_cf_node_block: break; case nir_cf_node_if: { nir_if *nif = nir_cf_node_as_if(cf_node); progress |= opt_peel_loop_initial_if_cf_list(&nif->then_list); progress |= opt_peel_loop_initial_if_cf_list(&nif->else_list); break; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(cf_node); progress |= opt_peel_loop_initial_if_cf_list(&loop->body); progress |= opt_peel_loop_initial_if(loop); break; } case nir_cf_node_function: unreachable("Invalid cf type"); } } return progress; } /** * These optimisations depend on nir_metadata_block_index and therefore must * not do anything to cause the metadata to become invalid. */ static bool opt_if_safe_cf_list(nir_builder *b, struct exec_list *cf_list) { bool progress = false; foreach_list_typed(nir_cf_node, cf_node, node, cf_list) { switch (cf_node->type) { case nir_cf_node_block: break; case nir_cf_node_if: { nir_if *nif = nir_cf_node_as_if(cf_node); progress |= opt_if_safe_cf_list(b, &nif->then_list); progress |= opt_if_safe_cf_list(b, &nif->else_list); progress |= opt_if_evaluate_condition_use(b, nif); break; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(cf_node); progress |= opt_if_safe_cf_list(b, &loop->body); progress |= opt_split_alu_of_phi(b, loop); break; } case nir_cf_node_function: unreachable("Invalid cf type"); } } return progress; } bool nir_opt_if(nir_shader *shader, bool aggressive_last_continue) { bool progress = false; nir_foreach_function(function, shader) { if (function->impl == NULL) continue; nir_builder b; nir_builder_init(&b, function->impl); nir_metadata_require(function->impl, nir_metadata_block_index | nir_metadata_dominance); progress = opt_if_safe_cf_list(&b, &function->impl->body); nir_metadata_preserve(function->impl, nir_metadata_block_index | nir_metadata_dominance); bool preserve = true; if (opt_if_cf_list(&b, &function->impl->body, aggressive_last_continue)) { preserve = false; progress = true; } if (opt_peel_loop_initial_if_cf_list(&function->impl->body)) { preserve = false; progress = true; /* If that made progress, we're no longer really in SSA form. We * need to convert registers back into SSA defs and clean up SSA defs * that don't dominate their uses. */ nir_lower_regs_to_ssa_impl(function->impl); } if (preserve) { nir_metadata_preserve(function->impl, nir_metadata_none); } else { nir_metadata_preserve(function->impl, nir_metadata_all); } } return progress; }