/* * Copyright © 2013 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 "brw_fs.h" #include "brw_cfg.h" /** @file brw_fs_sel_peephole.cpp * * This file contains the opt_peephole_sel() optimization pass that replaces * MOV instructions to the same destination in the "then" and "else" bodies of * an if statement with SEL instructions. */ /* Four MOVs seems to be pretty typical, so I picked the next power of two in * the hopes that it would handle almost anything possible in a single * pass. */ #define MAX_MOVS 8 /**< The maximum number of MOVs to attempt to match. */ using namespace brw; /** * Scans forwards from an IF counting consecutive MOV instructions in the * "then" and "else" blocks of the if statement. * * A pointer to the bblock_t following the IF is passed as the * argument. The function stores pointers to the MOV instructions in the * and arrays. * * \return the minimum number of MOVs found in the two branches or zero if * an error occurred. * * E.g.: * IF ... * then_mov[0] = MOV g4, ... * then_mov[1] = MOV g5, ... * then_mov[2] = MOV g6, ... * ELSE ... * else_mov[0] = MOV g4, ... * else_mov[1] = MOV g5, ... * else_mov[2] = MOV g7, ... * ENDIF * returns 3. */ static int count_movs_from_if(fs_inst *then_mov[MAX_MOVS], fs_inst *else_mov[MAX_MOVS], bblock_t *then_block, bblock_t *else_block) { int then_movs = 0; foreach_inst_in_block(fs_inst, inst, then_block) { if (then_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV || inst->flags_written()) break; then_mov[then_movs] = inst; then_movs++; } int else_movs = 0; foreach_inst_in_block(fs_inst, inst, else_block) { if (else_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV || inst->flags_written()) break; else_mov[else_movs] = inst; else_movs++; } return MIN2(then_movs, else_movs); } /** * Try to replace IF/MOV+/ELSE/MOV+/ENDIF with SEL. * * Many GLSL shaders contain the following pattern: * * x = condition ? foo : bar * * or * * if (...) a.xyzw = foo.xyzw; * else a.xyzw = bar.xyzw; * * The compiler emits an ir_if tree for this, since each subexpression might be * a complex tree that could have side-effects or short-circuit logic. * * However, the common case is to simply select one of two constants or * variable values---which is exactly what SEL is for. In this case, the * assembly looks like: * * (+f0) IF * MOV dst src0 * ... * ELSE * MOV dst src1 * ... * ENDIF * * where each pair of MOVs to a common destination and can be easily translated * into * * (+f0) SEL dst src0 src1 * * If src0 is an immediate value, we promote it to a temporary GRF. */ bool fs_visitor::opt_peephole_sel() { bool progress = false; foreach_block (block, cfg) { /* IF instructions, by definition, can only be found at the ends of * basic blocks. */ fs_inst *if_inst = (fs_inst *)block->end(); if (if_inst->opcode != BRW_OPCODE_IF) continue; fs_inst *else_mov[MAX_MOVS] = { NULL }; fs_inst *then_mov[MAX_MOVS] = { NULL }; bblock_t *then_block = block->next(); bblock_t *else_block = NULL; foreach_list_typed(bblock_link, child, link, &block->children) { if (child->block != then_block) { if (child->block->prev()->end()->opcode == BRW_OPCODE_ELSE) { else_block = child->block; } break; } } if (else_block == NULL) continue; int movs = count_movs_from_if(then_mov, else_mov, then_block, else_block); if (movs == 0) continue; /* Generate SEL instructions for pairs of MOVs to a common destination. */ for (int i = 0; i < movs; i++) { if (!then_mov[i] || !else_mov[i]) break; /* Check that the MOVs are the right form. */ if (!then_mov[i]->dst.equals(else_mov[i]->dst) || then_mov[i]->exec_size != else_mov[i]->exec_size || then_mov[i]->group != else_mov[i]->group || then_mov[i]->force_writemask_all != else_mov[i]->force_writemask_all || then_mov[i]->is_partial_write() || else_mov[i]->is_partial_write() || then_mov[i]->conditional_mod != BRW_CONDITIONAL_NONE || else_mov[i]->conditional_mod != BRW_CONDITIONAL_NONE) { movs = i; break; } /* Check that source types for mov operations match. */ if (then_mov[i]->src[0].type != else_mov[i]->src[0].type) { movs = i; break; } } if (movs == 0) continue; for (int i = 0; i < movs; i++) { const fs_builder ibld = fs_builder(this, then_block, then_mov[i]) .at(block, if_inst); if (then_mov[i]->src[0].equals(else_mov[i]->src[0])) { ibld.MOV(then_mov[i]->dst, then_mov[i]->src[0]); } else { /* Only the last source register can be a constant, so if the MOV * in the "then" clause uses a constant, we need to put it in a * temporary. */ fs_reg src0(then_mov[i]->src[0]); if (src0.file == IMM) { src0 = vgrf(glsl_type::float_type); src0.type = then_mov[i]->src[0].type; ibld.MOV(src0, then_mov[i]->src[0]); } set_predicate_inv(if_inst->predicate, if_inst->predicate_inverse, ibld.SEL(then_mov[i]->dst, src0, else_mov[i]->src[0])); } then_mov[i]->remove(then_block); else_mov[i]->remove(else_block); } progress = true; } if (progress) invalidate_live_intervals(); return progress; }