brw_fs_dead_code_eliminate.cpp revision 9919542f1cfff70524bc6117d19bf88e59159caa
1/* 2 * Copyright © 2014 Intel Corporation 3 * 4 * Permission is hereby granted, free of charge, to any person obtaining a 5 * copy of this software and associated documentation files (the "Software"), 6 * to deal in the Software without restriction, including without limitation 7 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 8 * and/or sell copies of the Software, and to permit persons to whom the 9 * Software is furnished to do so, subject to the following conditions: 10 * 11 * The above copyright notice and this permission notice (including the next 12 * paragraph) shall be included in all copies or substantial portions of the 13 * Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 21 * IN THE SOFTWARE. 22 */ 23 24#include "brw_fs.h" 25#include "brw_fs_live_variables.h" 26#include "brw_cfg.h" 27 28/** @file brw_fs_dead_code_eliminate.cpp 29 * 30 * Dataflow-aware dead code elimination. 31 * 32 * Walks the instruction list from the bottom, removing instructions that 33 * have results that both aren't used in later blocks and haven't been read 34 * yet in the tail end of this block. 35 */ 36 37/** 38 * Is it safe to eliminate the instruction? 39 */ 40static bool 41can_eliminate(const fs_inst *inst, BITSET_WORD *flag_live) 42{ 43 return !inst->is_control_flow() && 44 !inst->has_side_effects() && 45 !(flag_live[0] & inst->flags_written()) && 46 !inst->writes_accumulator; 47} 48 49/** 50 * Is it safe to omit the write, making the destination ARF null? 51 */ 52static bool 53can_omit_write(const fs_inst *inst) 54{ 55 switch (inst->opcode) { 56 case SHADER_OPCODE_UNTYPED_ATOMIC: 57 case SHADER_OPCODE_UNTYPED_ATOMIC_LOGICAL: 58 case SHADER_OPCODE_TYPED_ATOMIC: 59 case SHADER_OPCODE_TYPED_ATOMIC_LOGICAL: 60 return true; 61 default: 62 /* We can eliminate the destination write for ordinary instructions, 63 * but not most SENDs. 64 */ 65 if (inst->opcode < 128 && inst->mlen == 0) 66 return true; 67 68 /* It might not be safe for other virtual opcodes. */ 69 return false; 70 } 71} 72 73bool 74fs_visitor::dead_code_eliminate() 75{ 76 bool progress = false; 77 78 calculate_live_intervals(); 79 80 int num_vars = live_intervals->num_vars; 81 BITSET_WORD *live = rzalloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars)); 82 BITSET_WORD *flag_live = rzalloc_array(NULL, BITSET_WORD, 1); 83 84 foreach_block_reverse_safe(block, cfg) { 85 memcpy(live, live_intervals->block_data[block->num].liveout, 86 sizeof(BITSET_WORD) * BITSET_WORDS(num_vars)); 87 memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout, 88 sizeof(BITSET_WORD)); 89 90 foreach_inst_in_block_reverse_safe(fs_inst, inst, block) { 91 if (inst->dst.file == VGRF) { 92 const unsigned var = live_intervals->var_from_reg(inst->dst); 93 bool result_live = false; 94 95 for (unsigned i = 0; i < regs_written(inst); i++) 96 result_live |= BITSET_TEST(live, var + i); 97 98 if (!result_live && 99 (can_omit_write(inst) || can_eliminate(inst, flag_live))) { 100 inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type)); 101 progress = true; 102 } 103 } 104 105 if (inst->dst.is_null() && can_eliminate(inst, flag_live)) { 106 inst->opcode = BRW_OPCODE_NOP; 107 progress = true; 108 } 109 110 if (inst->dst.file == VGRF) { 111 if (!inst->is_partial_write()) { 112 int var = live_intervals->var_from_reg(inst->dst); 113 for (unsigned i = 0; i < regs_written(inst); i++) { 114 BITSET_CLEAR(live, var + i); 115 } 116 } 117 } 118 119 if (!inst->predicate && inst->exec_size >= 8) 120 flag_live[0] &= ~inst->flags_written(); 121 122 if (inst->opcode == BRW_OPCODE_NOP) { 123 inst->remove(block); 124 continue; 125 } 126 127 for (int i = 0; i < inst->sources; i++) { 128 if (inst->src[i].file == VGRF) { 129 int var = live_intervals->var_from_reg(inst->src[i]); 130 131 for (unsigned j = 0; j < regs_read(inst, i); j++) { 132 BITSET_SET(live, var + j); 133 } 134 } 135 } 136 137 flag_live[0] |= inst->flags_read(devinfo); 138 } 139 } 140 141 ralloc_free(live); 142 ralloc_free(flag_live); 143 144 if (progress) 145 invalidate_live_intervals(); 146 147 return progress; 148} 149