/* * 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. */ /** * Scans forwards from an IF counting consecutive MOV instructions in the * "then" and "else" blocks of the if statement. * * A pointer to the fs_inst* for 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], fs_inst *if_inst, fs_inst *else_inst) { fs_inst *m = if_inst; assert(m->opcode == BRW_OPCODE_IF); m = (fs_inst *) m->next; int then_movs = 0; while (then_movs < MAX_MOVS && m->opcode == BRW_OPCODE_MOV) { then_mov[then_movs] = m; m = (fs_inst *) m->next; then_movs++; } m = (fs_inst *) else_inst->next; int else_movs = 0; while (else_movs < MAX_MOVS && m->opcode == BRW_OPCODE_MOV) { else_mov[else_movs] = m; m = (fs_inst *) m->next; 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; cfg_t cfg(&instructions); for (int b = 0; b < cfg.num_blocks; b++) { bblock_t *block = cfg.blocks[b]; /* 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; if (!block->else_inst) continue; fs_inst *else_inst = (fs_inst *) block->else_inst; assert(else_inst->opcode == BRW_OPCODE_ELSE); fs_inst *else_mov[MAX_MOVS] = { NULL }; fs_inst *then_mov[MAX_MOVS] = { NULL }; int movs = count_movs_from_if(then_mov, else_mov, if_inst, else_inst); if (movs == 0) continue; fs_inst *sel_inst[MAX_MOVS] = { NULL }; fs_inst *mov_imm_inst[MAX_MOVS] = { NULL }; /* 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]->is_partial_write() || else_mov[i]->is_partial_write()) { 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 (!then_mov[i]->src[0].equals(else_mov[i]->src[0])) { /* 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 = fs_reg(this, glsl_type::float_type); src0.type = then_mov[i]->src[0].type; mov_imm_inst[i] = MOV(src0, then_mov[i]->src[0]); } sel_inst[i] = SEL(then_mov[i]->dst, src0, else_mov[i]->src[0]); if (brw->gen == 6 && if_inst->conditional_mod) { /* For Sandybridge with IF with embedded comparison */ sel_inst[i]->predicate = BRW_PREDICATE_NORMAL; } else { /* Separate CMP and IF instructions */ sel_inst[i]->predicate = if_inst->predicate; sel_inst[i]->predicate_inverse = if_inst->predicate_inverse; } } else { sel_inst[i] = MOV(then_mov[i]->dst, then_mov[i]->src[0]); } } if (movs == 0) continue; /* Emit a CMP if our IF used the embedded comparison */ if (brw->gen == 6 && if_inst->conditional_mod) { fs_inst *cmp_inst = CMP(reg_null_d, if_inst->src[0], if_inst->src[1], if_inst->conditional_mod); if_inst->insert_before(cmp_inst); } for (int i = 0; i < movs; i++) { if (mov_imm_inst[i]) if_inst->insert_before(mov_imm_inst[i]); if_inst->insert_before(sel_inst[i]); then_mov[i]->remove(); else_mov[i]->remove(); } progress = true; } if (progress) invalidate_live_intervals(); return progress; }