1 /* Localize comdats. 2 Copyright (C) 2014-2018 Free Software Foundation, Inc. 3 4 This file is part of GCC. 5 6 GCC is free software; you can redistribute it and/or modify it under 7 the terms of the GNU General Public License as published by the Free 8 Software Foundation; either version 3, or (at your option) any later 9 version. 10 11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GCC; see the file COPYING3. If not see 18 <http://www.gnu.org/licenses/>. */ 19 20 /* This is very simple pass that looks for static symbols that are used 21 exlusively by symbol within one comdat group. In this case it makes 22 sense to bring the symbol itself into the group to avoid dead code 23 that would arrise when the comdat group from current unit is replaced 24 by a different copy. Consider for example: 25 26 static int q(void) 27 { 28 .... 29 } 30 inline int t(void) 31 { 32 return q(); 33 } 34 35 if Q is used only by T, it makes sense to put Q into T's comdat group. 36 37 The pass solve simple dataflow across the callgraph trying to prove what 38 symbols are used exclusively from a given comdat group. 39 40 The implementation maintains a queue linked by AUX pointer terminated by 41 pointer value 1. Lattice values are NULL for TOP, actual comdat group, or 42 ERROR_MARK_NODE for bottom. 43 44 TODO: When symbol is used only by comdat symbols, but from different groups, 45 it would make sense to produce a new comdat group for it with anonymous name. 46 47 TODO2: We can't mix variables and functions within one group. Currently 48 we just give up on references of symbols of different types. We also should 49 handle this by anonymous comdat group section. */ 50 51 #include "config.h" 52 #include "system.h" 53 #include "coretypes.h" 54 #include "tm.h" 55 #include "tree.h" 56 #include "tree-pass.h" 57 #include "cgraph.h" 58 59 /* Main dataflow loop propagating comdat groups across 60 the symbol table. All references to SYMBOL are examined 61 and NEWGROUP is updated accordingly. MAP holds current lattice 62 values for individual symbols. */ 63 64 tree 65 propagate_comdat_group (struct symtab_node *symbol, 66 tree newgroup, hash_map<symtab_node *, tree> &map) 67 { 68 int i; 69 struct ipa_ref *ref; 70 71 /* Walk all references to SYMBOL, recursively dive into aliases. */ 72 73 for (i = 0; 74 symbol->iterate_referring (i, ref) 75 && newgroup != error_mark_node; i++) 76 { 77 struct symtab_node *symbol2 = ref->referring; 78 79 if (ref->use == IPA_REF_ALIAS) 80 { 81 newgroup = propagate_comdat_group (symbol2, newgroup, map); 82 continue; 83 } 84 85 /* One COMDAT group can not hold both variables and functions at 86 a same time. For now we just go to BOTTOM, in future we may 87 invent special comdat groups for this case. */ 88 89 if (symbol->type != symbol2->type) 90 { 91 newgroup = error_mark_node; 92 break; 93 } 94 95 /* If we see inline clone, its comdat group actually 96 corresponds to the comdat group of the function it is inlined 97 to. */ 98 99 if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2)) 100 { 101 if (cn->global.inlined_to) 102 symbol2 = cn->global.inlined_to; 103 } 104 105 /* The actual merge operation. */ 106 107 tree *val2 = map.get (symbol2); 108 109 if (val2 && *val2 != newgroup) 110 { 111 if (!newgroup) 112 newgroup = *val2; 113 else 114 newgroup = error_mark_node; 115 } 116 } 117 118 /* If we analyze function, walk also callers. */ 119 120 cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol); 121 122 if (cnode) 123 for (struct cgraph_edge * edge = cnode->callers; 124 edge && newgroup != error_mark_node; edge = edge->next_caller) 125 { 126 struct symtab_node *symbol2 = edge->caller; 127 128 if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2)) 129 { 130 /* Thunks can not call across section boundary. */ 131 if (cn->thunk.thunk_p) 132 newgroup = propagate_comdat_group (symbol2, newgroup, map); 133 /* If we see inline clone, its comdat group actually 134 corresponds to the comdat group of the function it 135 is inlined to. */ 136 if (cn->global.inlined_to) 137 symbol2 = cn->global.inlined_to; 138 } 139 140 /* The actual merge operation. */ 141 142 tree *val2 = map.get (symbol2); 143 144 if (val2 && *val2 != newgroup) 145 { 146 if (!newgroup) 147 newgroup = *val2; 148 else 149 newgroup = error_mark_node; 150 } 151 } 152 return newgroup; 153 } 154 155 156 /* Add all references of SYMBOL that are defined into queue started by FIRST 157 and linked by AUX pointer (unless they are already enqueued). 158 Walk recursively inlined functions. */ 159 160 void 161 enqueue_references (symtab_node **first, 162 symtab_node *symbol) 163 { 164 int i; 165 struct ipa_ref *ref = NULL; 166 167 for (i = 0; symbol->iterate_reference (i, ref); i++) 168 { 169 symtab_node *node = ref->referred->ultimate_alias_target (); 170 171 /* Always keep thunks in same sections as target function. */ 172 if (is_a <cgraph_node *>(node)) 173 node = dyn_cast <cgraph_node *> (node)->function_symbol (); 174 if (!node->aux && node->definition) 175 { 176 node->aux = *first; 177 *first = node; 178 } 179 } 180 181 if (cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol)) 182 { 183 struct cgraph_edge *edge; 184 185 for (edge = cnode->callees; edge; edge = edge->next_callee) 186 if (!edge->inline_failed) 187 enqueue_references (first, edge->callee); 188 else 189 { 190 symtab_node *node = edge->callee->ultimate_alias_target (); 191 192 /* Always keep thunks in same sections as target function. */ 193 if (is_a <cgraph_node *>(node)) 194 node = dyn_cast <cgraph_node *> (node)->function_symbol (); 195 if (!node->aux && node->definition) 196 { 197 node->aux = *first; 198 *first = node; 199 } 200 } 201 } 202 } 203 204 /* Set comdat group of SYMBOL to GROUP. 205 Callback for for_node_and_aliases. */ 206 207 bool 208 set_comdat_group (symtab_node *symbol, 209 void *head_p) 210 { 211 symtab_node *head = (symtab_node *)head_p; 212 213 gcc_assert (!symbol->get_comdat_group ()); 214 if (symbol->real_symbol_p ()) 215 { 216 symbol->set_comdat_group (head->get_comdat_group ()); 217 symbol->add_to_same_comdat_group (head); 218 } 219 return false; 220 } 221 222 /* Set comdat group of SYMBOL to GROUP. 223 Callback for for_node_thunks_and_aliases. */ 224 225 bool 226 set_comdat_group_1 (cgraph_node *symbol, 227 void *head_p) 228 { 229 return set_comdat_group (symbol, head_p); 230 } 231 232 /* The actual pass with the main dataflow loop. */ 233 234 static unsigned int 235 ipa_comdats (void) 236 { 237 hash_map<symtab_node *, tree> map (251); 238 hash_map<tree, symtab_node *> comdat_head_map (251); 239 symtab_node *symbol; 240 bool comdat_group_seen = false; 241 symtab_node *first = (symtab_node *) (void *) 1; 242 tree group; 243 244 /* Start the dataflow by assigning comdat group to symbols that are in comdat 245 groups already. All other externally visible symbols must stay, we use 246 ERROR_MARK_NODE as bottom for the propagation. */ 247 248 FOR_EACH_DEFINED_SYMBOL (symbol) 249 if (!symbol->real_symbol_p ()) 250 ; 251 else if ((group = symbol->get_comdat_group ()) != NULL) 252 { 253 map.put (symbol, group); 254 comdat_head_map.put (group, symbol); 255 comdat_group_seen = true; 256 257 /* Mark the symbol so we won't waste time visiting it for dataflow. */ 258 symbol->aux = (symtab_node *) (void *) 1; 259 } 260 /* See symbols that can not be privatized to comdats; that is externally 261 visible symbols or otherwise used ones. We also do not want to mangle 262 user section names. */ 263 else if (symbol->externally_visible 264 || symbol->force_output 265 || symbol->used_from_other_partition 266 || TREE_THIS_VOLATILE (symbol->decl) 267 || symbol->get_section () 268 || (TREE_CODE (symbol->decl) == FUNCTION_DECL 269 && (DECL_STATIC_CONSTRUCTOR (symbol->decl) 270 || DECL_STATIC_DESTRUCTOR (symbol->decl)))) 271 { 272 symtab_node *target = symbol->ultimate_alias_target (); 273 274 /* Always keep thunks in same sections as target function. */ 275 if (is_a <cgraph_node *>(target)) 276 target = dyn_cast <cgraph_node *> (target)->function_symbol (); 277 map.put (target, error_mark_node); 278 279 /* Mark the symbol so we won't waste time visiting it for dataflow. */ 280 symbol->aux = (symtab_node *) (void *) 1; 281 } 282 else 283 { 284 /* Enqueue symbol for dataflow. */ 285 symbol->aux = first; 286 first = symbol; 287 } 288 289 if (!comdat_group_seen) 290 { 291 FOR_EACH_DEFINED_SYMBOL (symbol) 292 symbol->aux = NULL; 293 return 0; 294 } 295 296 /* The actual dataflow. */ 297 298 while (first != (void *) 1) 299 { 300 tree group = NULL; 301 tree newgroup, *val; 302 303 symbol = first; 304 first = (symtab_node *)first->aux; 305 306 /* Get current lattice value of SYMBOL. */ 307 val = map.get (symbol); 308 if (val) 309 group = *val; 310 311 /* If it is bottom, there is nothing to do; do not clear AUX 312 so we won't re-queue the symbol. */ 313 if (group == error_mark_node) 314 continue; 315 316 newgroup = propagate_comdat_group (symbol, group, map); 317 318 /* If nothing changed, proceed to next symbol. */ 319 if (newgroup == group) 320 { 321 symbol->aux = NULL; 322 continue; 323 } 324 325 /* Update lattice value and enqueue all references for re-visiting. */ 326 gcc_assert (newgroup); 327 if (val) 328 *val = newgroup; 329 else 330 map.put (symbol, newgroup); 331 enqueue_references (&first, symbol); 332 333 /* We may need to revisit the symbol unless it is BOTTOM. */ 334 if (newgroup != error_mark_node) 335 symbol->aux = NULL; 336 } 337 338 /* Finally assign symbols to the sections. */ 339 340 FOR_EACH_DEFINED_SYMBOL (symbol) 341 { 342 struct cgraph_node *fun; 343 symbol->aux = NULL; 344 if (!symbol->get_comdat_group () 345 && !symbol->alias 346 && (!(fun = dyn_cast <cgraph_node *> (symbol)) 347 || !fun->thunk.thunk_p) 348 && symbol->real_symbol_p ()) 349 { 350 tree *val = map.get (symbol); 351 352 /* A NULL here means that SYMBOL is unreachable in the definition 353 of ipa-comdats. Either ipa-comdats is wrong about this or someone 354 forgot to cleanup and remove unreachable functions earlier. */ 355 gcc_assert (val); 356 357 tree group = *val; 358 359 if (group == error_mark_node) 360 continue; 361 if (dump_file) 362 { 363 fprintf (dump_file, "Localizing symbol\n"); 364 symbol->dump (dump_file); 365 fprintf (dump_file, "To group: %s\n", IDENTIFIER_POINTER (group)); 366 } 367 if (is_a <cgraph_node *> (symbol)) 368 dyn_cast <cgraph_node *>(symbol)->call_for_symbol_thunks_and_aliases 369 (set_comdat_group_1, 370 *comdat_head_map.get (group), 371 true); 372 else 373 symbol->call_for_symbol_and_aliases 374 (set_comdat_group, 375 *comdat_head_map.get (group), 376 true); 377 } 378 } 379 return 0; 380 } 381 382 namespace { 383 384 const pass_data pass_data_ipa_comdats = 385 { 386 IPA_PASS, /* type */ 387 "comdats", /* name */ 388 OPTGROUP_NONE, /* optinfo_flags */ 389 TV_IPA_COMDATS, /* tv_id */ 390 0, /* properties_required */ 391 0, /* properties_provided */ 392 0, /* properties_destroyed */ 393 0, /* todo_flags_start */ 394 0, /* todo_flags_finish */ 395 }; 396 397 class pass_ipa_comdats : public ipa_opt_pass_d 398 { 399 public: 400 pass_ipa_comdats (gcc::context *ctxt) 401 : ipa_opt_pass_d (pass_data_ipa_comdats, ctxt, 402 NULL, /* generate_summary */ 403 NULL, /* write_summary */ 404 NULL, /* read_summary */ 405 NULL, /* write_optimization_summary */ 406 NULL, /* read_optimization_summary */ 407 NULL, /* stmt_fixup */ 408 0, /* function_transform_todo_flags_start */ 409 NULL, /* function_transform */ 410 NULL) /* variable_transform */ 411 {} 412 413 /* opt_pass methods: */ 414 virtual bool gate (function *); 415 virtual unsigned int execute (function *) { return ipa_comdats (); } 416 417 }; // class pass_ipa_comdats 418 419 bool 420 pass_ipa_comdats::gate (function *) 421 { 422 return HAVE_COMDAT_GROUP; 423 } 424 425 } // anon namespace 426 427 ipa_opt_pass_d * 428 make_pass_ipa_comdats (gcc::context *ctxt) 429 { 430 return new pass_ipa_comdats (ctxt); 431 } 432