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_cfg.h" 26 #include "brw_eu.h" 27 28 /** @file brw_fs_cmod_propagation.cpp 29 * 30 * Implements a pass that propagates the conditional modifier from a CMP x 0.0 31 * instruction into the instruction that generated x. For instance, in this 32 * sequence 33 * 34 * add(8) g70<1>F g69<8,8,1>F 4096F 35 * cmp.ge.f0(8) null g70<8,8,1>F 0F 36 * 37 * we can do the comparison as part of the ADD instruction directly: 38 * 39 * add.ge.f0(8) g70<1>F g69<8,8,1>F 4096F 40 * 41 * If there had been a use of the flag register and another CMP using g70 42 * 43 * add.ge.f0(8) g70<1>F g69<8,8,1>F 4096F 44 * (+f0) sel(8) g71<F> g72<8,8,1>F g73<8,8,1>F 45 * cmp.ge.f0(8) null g70<8,8,1>F 0F 46 * 47 * we can recognize that the CMP is generating the flag value that already 48 * exists and therefore remove the instruction. 49 */ 50 51 static bool 52 opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block) 53 { 54 bool progress = false; 55 int ip = block->end_ip + 1; 56 57 foreach_inst_in_block_reverse_safe(fs_inst, inst, block) { 58 ip--; 59 60 if ((inst->opcode != BRW_OPCODE_AND && 61 inst->opcode != BRW_OPCODE_CMP && 62 inst->opcode != BRW_OPCODE_MOV) || 63 inst->predicate != BRW_PREDICATE_NONE || 64 !inst->dst.is_null() || 65 inst->src[0].file != VGRF || 66 inst->src[0].abs) 67 continue; 68 69 /* Only an AND.NZ can be propagated. Many AND.Z instructions are 70 * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code). 71 * Propagating those would require inverting the condition on the CMP. 72 * This changes both the flag value and the register destination of the 73 * CMP. That result may be used elsewhere, so we can't change its value 74 * on a whim. 75 */ 76 if (inst->opcode == BRW_OPCODE_AND && 77 !(inst->src[1].is_one() && 78 inst->conditional_mod == BRW_CONDITIONAL_NZ && 79 !inst->src[0].negate)) 80 continue; 81 82 if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero()) 83 continue; 84 85 if (inst->opcode == BRW_OPCODE_MOV && 86 inst->conditional_mod != BRW_CONDITIONAL_NZ) 87 continue; 88 89 bool read_flag = false; 90 foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) { 91 if (regions_overlap(scan_inst->dst, scan_inst->size_written, 92 inst->src[0], inst->size_read(0))) { 93 if (scan_inst->is_partial_write() || 94 scan_inst->dst.offset != inst->src[0].offset || 95 scan_inst->exec_size != inst->exec_size) 96 break; 97 98 /* CMP's result is the same regardless of dest type. */ 99 if (inst->conditional_mod == BRW_CONDITIONAL_NZ && 100 scan_inst->opcode == BRW_OPCODE_CMP && 101 (inst->dst.type == BRW_REGISTER_TYPE_D || 102 inst->dst.type == BRW_REGISTER_TYPE_UD)) { 103 inst->remove(block); 104 progress = true; 105 break; 106 } 107 108 /* If the AND wasn't handled by the previous case, it isn't safe 109 * to remove it. 110 */ 111 if (inst->opcode == BRW_OPCODE_AND) 112 break; 113 114 /* Comparisons operate differently for ints and floats */ 115 if (scan_inst->dst.type != inst->dst.type && 116 (scan_inst->dst.type == BRW_REGISTER_TYPE_F || 117 inst->dst.type == BRW_REGISTER_TYPE_F)) 118 break; 119 120 /* If the instruction generating inst's source also wrote the 121 * flag, and inst is doing a simple .nz comparison, then inst 122 * is redundant - the appropriate value is already in the flag 123 * register. Delete inst. 124 */ 125 if (inst->conditional_mod == BRW_CONDITIONAL_NZ && 126 !inst->src[0].negate && 127 scan_inst->flags_written()) { 128 inst->remove(block); 129 progress = true; 130 break; 131 } 132 133 /* The conditional mod of the CMP/CMPN instructions behaves 134 * specially because the flag output is not calculated from the 135 * result of the instruction, but the other way around, which 136 * means that even if the condmod to propagate and the condmod 137 * from the CMP instruction are the same they will in general give 138 * different results because they are evaluated based on different 139 * inputs. 140 */ 141 if (scan_inst->opcode == BRW_OPCODE_CMP || 142 scan_inst->opcode == BRW_OPCODE_CMPN) 143 break; 144 145 /* Otherwise, try propagating the conditional. */ 146 enum brw_conditional_mod cond = 147 inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod) 148 : inst->conditional_mod; 149 150 if (scan_inst->can_do_cmod() && 151 ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) || 152 scan_inst->conditional_mod == cond)) { 153 scan_inst->conditional_mod = cond; 154 inst->remove(block); 155 progress = true; 156 } 157 break; 158 } 159 160 if (scan_inst->flags_written()) 161 break; 162 163 read_flag = read_flag || scan_inst->flags_read(devinfo); 164 } 165 } 166 167 return progress; 168 } 169 170 bool 171 fs_visitor::opt_cmod_propagation() 172 { 173 bool progress = false; 174 175 foreach_block_reverse(block, cfg) { 176 progress = opt_cmod_propagation_local(devinfo, block) || progress; 177 } 178 179 if (progress) 180 invalidate_live_intervals(); 181 182 return progress; 183 } 184
