/* * Copyright © 2014 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. * * Authors: * Jason Ekstrand (jason@jlekstrand.net) * */ #include "nir.h" /* * Implements a small peephole optimization that looks for * * if (cond) { * * } else { * * } * phi * ... * phi * * and replaces it with a series of selects. It can also handle the case * where, instead of being empty, the if may contain some move operations * whose only use is one of the following phi nodes. This happens all the * time when the SSA form comes from a conditional assignment with a * swizzle. */ struct peephole_select_state { void *mem_ctx; bool progress; }; static bool are_all_move_to_phi(nir_block *block) { nir_foreach_instr(block, instr) { if (instr->type != nir_instr_type_alu) return false; /* It must be a move operation */ nir_alu_instr *mov = nir_instr_as_alu(instr); if (mov->op != nir_op_fmov && mov->op != nir_op_imov) return false; /* Can't handle saturate */ if (mov->dest.saturate) return false; /* It must be SSA */ if (!mov->dest.dest.is_ssa) return false; /* It cannot have any if-uses */ if (mov->dest.dest.ssa.if_uses->entries != 0) return false; /* The only uses of this definition must be phi's in the successor */ struct set_entry *entry; set_foreach(mov->dest.dest.ssa.uses, entry) { const nir_instr *dest_instr = entry->key; if (dest_instr->type != nir_instr_type_phi || dest_instr->block != block->successors[0]) return false; } } return true; } static bool nir_opt_peephole_select_block(nir_block *block, void *void_state) { struct peephole_select_state *state = void_state; /* If the block is empty, then it certainly doesn't have any phi nodes, * so we can skip it. This also ensures that we do an early skip on the * end block of the function which isn't actually attached to the CFG. */ if (exec_list_is_empty(&block->instr_list)) return true; if (nir_cf_node_is_first(&block->cf_node)) return true; nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node); if (prev_node->type != nir_cf_node_if) return true; nir_if *if_stmt = nir_cf_node_as_if(prev_node); nir_cf_node *then_node = nir_if_first_then_node(if_stmt); nir_cf_node *else_node = nir_if_first_else_node(if_stmt); /* We can only have one block in each side ... */ if (nir_if_last_then_node(if_stmt) != then_node || nir_if_last_else_node(if_stmt) != else_node) return true; nir_block *then_block = nir_cf_node_as_block(then_node); nir_block *else_block = nir_cf_node_as_block(else_node); /* ... and those blocks must only contain move-to-phi. */ if (!are_all_move_to_phi(then_block) || !are_all_move_to_phi(else_block)) return true; /* At this point, we know that the previous CFG node is an if-then * statement containing only moves to phi nodes in this block. We can * just remove that entire CF node and replace all of the phi nodes with * selects. */ nir_foreach_instr_safe(block, instr) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); nir_alu_instr *sel = nir_alu_instr_create(state->mem_ctx, nir_op_bcsel); sel->src[0].src = nir_src_copy(if_stmt->condition, state->mem_ctx); /* Splat the condition to all channels */ memset(sel->src[0].swizzle, 0, sizeof sel->src[0].swizzle); assert(exec_list_length(&phi->srcs) == 2); nir_foreach_phi_src(phi, src) { assert(src->pred == then_block || src->pred == else_block); assert(src->src.is_ssa); unsigned idx = src->pred == then_block ? 1 : 2; if (src->src.ssa->parent_instr->block == src->pred) { /* We already know that this instruction must be a move with * this phi's in this block as its only users. */ nir_alu_instr *mov = nir_instr_as_alu(src->src.ssa->parent_instr); assert(mov->instr.type == nir_instr_type_alu); assert(mov->op == nir_op_fmov || mov->op == nir_op_imov); sel->src[idx].src = nir_src_copy(mov->src[0].src, state->mem_ctx); sel->src[idx].negate = mov->src[0].negate; sel->src[idx].abs = mov->src[0].abs; memcpy(sel->src[idx].swizzle, mov->src[0].swizzle, 4); } else { sel->src[idx].src = nir_src_copy(src->src, state->mem_ctx); } } nir_ssa_dest_init(&sel->instr, &sel->dest.dest, phi->dest.ssa.num_components, phi->dest.ssa.name); sel->dest.write_mask = (1 << phi->dest.ssa.num_components) - 1; nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(&sel->dest.dest.ssa), state->mem_ctx); nir_instr_insert_before(&phi->instr, &sel->instr); nir_instr_remove(&phi->instr); } nir_cf_node_remove(&if_stmt->cf_node); state->progress = true; return true; } static bool nir_opt_peephole_select_impl(nir_function_impl *impl) { struct peephole_select_state state; state.mem_ctx = ralloc_parent(impl); state.progress = false; nir_foreach_block(impl, nir_opt_peephole_select_block, &state); if (state.progress) nir_metadata_preserve(impl, nir_metadata_none); return state.progress; } bool nir_opt_peephole_select(nir_shader *shader) { bool progress = false; nir_foreach_overload(shader, overload) { if (overload->impl) progress |= nir_opt_peephole_select_impl(overload->impl); } return progress; }