1 /* Generic routines for manipulating PHIs 2 Copyright (C) 2003-2013 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 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3, or (at your option) 9 any later version. 10 11 GCC is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License 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 #include "config.h" 21 #include "system.h" 22 #include "coretypes.h" 23 #include "tm.h" 24 #include "tree.h" 25 #include "ggc.h" 26 #include "basic-block.h" 27 #include "tree-flow.h" 28 #include "diagnostic-core.h" 29 #include "gimple.h" 30 31 /* Rewriting a function into SSA form can create a huge number of PHIs 32 many of which may be thrown away shortly after their creation if jumps 33 were threaded through PHI nodes. 34 35 While our garbage collection mechanisms will handle this situation, it 36 is extremely wasteful to create nodes and throw them away, especially 37 when the nodes can be reused. 38 39 For PR 8361, we can significantly reduce the number of nodes allocated 40 and thus the total amount of memory allocated by managing PHIs a 41 little. This additionally helps reduce the amount of work done by the 42 garbage collector. Similar results have been seen on a wider variety 43 of tests (such as the compiler itself). 44 45 PHI nodes have different sizes, so we can't have a single list of all 46 the PHI nodes as it would be too expensive to walk down that list to 47 find a PHI of a suitable size. 48 49 Instead we have an array of lists of free PHI nodes. The array is 50 indexed by the number of PHI alternatives that PHI node can hold. 51 Except for the last array member, which holds all remaining PHI 52 nodes. 53 54 So to find a free PHI node, we compute its index into the free PHI 55 node array and see if there are any elements with an exact match. 56 If so, then we are done. Otherwise, we test the next larger size 57 up and continue until we are in the last array element. 58 59 We do not actually walk members of the last array element. While it 60 might allow us to pick up a few reusable PHI nodes, it could potentially 61 be very expensive if the program has released a bunch of large PHI nodes, 62 but keeps asking for even larger PHI nodes. Experiments have shown that 63 walking the elements of the last array entry would result in finding less 64 than .1% additional reusable PHI nodes. 65 66 Note that we can never have less than two PHI argument slots. Thus, 67 the -2 on all the calculations below. */ 68 69 #define NUM_BUCKETS 10 70 static GTY ((deletable (""))) vec<gimple, va_gc> *free_phinodes[NUM_BUCKETS - 2]; 71 static unsigned long free_phinode_count; 72 73 static int ideal_phi_node_len (int); 74 75 unsigned int phi_nodes_reused; 76 unsigned int phi_nodes_created; 77 78 /* Dump some simple statistics regarding the re-use of PHI nodes. */ 79 80 void 81 phinodes_print_statistics (void) 82 { 83 fprintf (stderr, "PHI nodes allocated: %u\n", phi_nodes_created); 84 fprintf (stderr, "PHI nodes reused: %u\n", phi_nodes_reused); 85 } 86 87 /* Allocate a PHI node with at least LEN arguments. If the free list 88 happens to contain a PHI node with LEN arguments or more, return 89 that one. */ 90 91 static inline gimple 92 allocate_phi_node (size_t len) 93 { 94 gimple phi; 95 size_t bucket = NUM_BUCKETS - 2; 96 size_t size = sizeof (struct gimple_statement_phi) 97 + (len - 1) * sizeof (struct phi_arg_d); 98 99 if (free_phinode_count) 100 for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++) 101 if (free_phinodes[bucket]) 102 break; 103 104 /* If our free list has an element, then use it. */ 105 if (bucket < NUM_BUCKETS - 2 106 && gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len) 107 { 108 free_phinode_count--; 109 phi = free_phinodes[bucket]->pop (); 110 if (free_phinodes[bucket]->is_empty ()) 111 vec_free (free_phinodes[bucket]); 112 if (GATHER_STATISTICS) 113 phi_nodes_reused++; 114 } 115 else 116 { 117 phi = ggc_alloc_gimple_statement_d (size); 118 if (GATHER_STATISTICS) 119 { 120 enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI); 121 phi_nodes_created++; 122 gimple_alloc_counts[(int) kind]++; 123 gimple_alloc_sizes[(int) kind] += size; 124 } 125 } 126 127 return phi; 128 } 129 130 /* Given LEN, the original number of requested PHI arguments, return 131 a new, "ideal" length for the PHI node. The "ideal" length rounds 132 the total size of the PHI node up to the next power of two bytes. 133 134 Rounding up will not result in wasting any memory since the size request 135 will be rounded up by the GC system anyway. [ Note this is not entirely 136 true since the original length might have fit on one of the special 137 GC pages. ] By rounding up, we may avoid the need to reallocate the 138 PHI node later if we increase the number of arguments for the PHI. */ 139 140 static int 141 ideal_phi_node_len (int len) 142 { 143 size_t size, new_size; 144 int log2, new_len; 145 146 /* We do not support allocations of less than two PHI argument slots. */ 147 if (len < 2) 148 len = 2; 149 150 /* Compute the number of bytes of the original request. */ 151 size = sizeof (struct gimple_statement_phi) 152 + (len - 1) * sizeof (struct phi_arg_d); 153 154 /* Round it up to the next power of two. */ 155 log2 = ceil_log2 (size); 156 new_size = 1 << log2; 157 158 /* Now compute and return the number of PHI argument slots given an 159 ideal size allocation. */ 160 new_len = len + (new_size - size) / sizeof (struct phi_arg_d); 161 return new_len; 162 } 163 164 /* Return a PHI node with LEN argument slots for variable VAR. */ 165 166 static gimple 167 make_phi_node (tree var, int len) 168 { 169 gimple phi; 170 int capacity, i; 171 172 capacity = ideal_phi_node_len (len); 173 174 phi = allocate_phi_node (capacity); 175 176 /* We need to clear the entire PHI node, including the argument 177 portion, because we represent a "missing PHI argument" by placing 178 NULL_TREE in PHI_ARG_DEF. */ 179 memset (phi, 0, (sizeof (struct gimple_statement_phi) 180 - sizeof (struct phi_arg_d) 181 + sizeof (struct phi_arg_d) * len)); 182 phi->gsbase.code = GIMPLE_PHI; 183 gimple_init_singleton (phi); 184 phi->gimple_phi.nargs = len; 185 phi->gimple_phi.capacity = capacity; 186 if (!var) 187 ; 188 else if (TREE_CODE (var) == SSA_NAME) 189 gimple_phi_set_result (phi, var); 190 else 191 gimple_phi_set_result (phi, make_ssa_name (var, phi)); 192 193 for (i = 0; i < capacity; i++) 194 { 195 use_operand_p imm; 196 197 gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION); 198 imm = gimple_phi_arg_imm_use_ptr (phi, i); 199 imm->use = gimple_phi_arg_def_ptr (phi, i); 200 imm->prev = NULL; 201 imm->next = NULL; 202 imm->loc.stmt = phi; 203 } 204 205 return phi; 206 } 207 208 /* We no longer need PHI, release it so that it may be reused. */ 209 210 void 211 release_phi_node (gimple phi) 212 { 213 size_t bucket; 214 size_t len = gimple_phi_capacity (phi); 215 size_t x; 216 217 for (x = 0; x < gimple_phi_num_args (phi); x++) 218 { 219 use_operand_p imm; 220 imm = gimple_phi_arg_imm_use_ptr (phi, x); 221 delink_imm_use (imm); 222 } 223 224 bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len; 225 bucket -= 2; 226 vec_safe_push (free_phinodes[bucket], phi); 227 free_phinode_count++; 228 } 229 230 231 /* Resize an existing PHI node. The only way is up. Return the 232 possibly relocated phi. */ 233 234 static gimple 235 resize_phi_node (gimple phi, size_t len) 236 { 237 size_t old_size, i; 238 gimple new_phi; 239 240 gcc_assert (len > gimple_phi_capacity (phi)); 241 242 /* The garbage collector will not look at the PHI node beyond the 243 first PHI_NUM_ARGS elements. Therefore, all we have to copy is a 244 portion of the PHI node currently in use. */ 245 old_size = sizeof (struct gimple_statement_phi) 246 + (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d); 247 248 new_phi = allocate_phi_node (len); 249 250 memcpy (new_phi, phi, old_size); 251 252 for (i = 0; i < gimple_phi_num_args (new_phi); i++) 253 { 254 use_operand_p imm, old_imm; 255 imm = gimple_phi_arg_imm_use_ptr (new_phi, i); 256 old_imm = gimple_phi_arg_imm_use_ptr (phi, i); 257 imm->use = gimple_phi_arg_def_ptr (new_phi, i); 258 relink_imm_use_stmt (imm, old_imm, new_phi); 259 } 260 261 new_phi->gimple_phi.capacity = len; 262 263 for (i = gimple_phi_num_args (new_phi); i < len; i++) 264 { 265 use_operand_p imm; 266 267 gimple_phi_arg_set_location (new_phi, i, UNKNOWN_LOCATION); 268 imm = gimple_phi_arg_imm_use_ptr (new_phi, i); 269 imm->use = gimple_phi_arg_def_ptr (new_phi, i); 270 imm->prev = NULL; 271 imm->next = NULL; 272 imm->loc.stmt = new_phi; 273 } 274 275 return new_phi; 276 } 277 278 /* Reserve PHI arguments for a new edge to basic block BB. */ 279 280 void 281 reserve_phi_args_for_new_edge (basic_block bb) 282 { 283 size_t len = EDGE_COUNT (bb->preds); 284 size_t cap = ideal_phi_node_len (len + 4); 285 gimple_stmt_iterator gsi; 286 287 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 288 { 289 gimple stmt = gsi_stmt (gsi); 290 291 if (len > gimple_phi_capacity (stmt)) 292 { 293 gimple new_phi = resize_phi_node (stmt, cap); 294 295 /* The result of the PHI is defined by this PHI node. */ 296 SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi; 297 gsi_set_stmt (&gsi, new_phi); 298 299 release_phi_node (stmt); 300 stmt = new_phi; 301 } 302 303 /* We represent a "missing PHI argument" by placing NULL_TREE in 304 the corresponding slot. If PHI arguments were added 305 immediately after an edge is created, this zeroing would not 306 be necessary, but unfortunately this is not the case. For 307 example, the loop optimizer duplicates several basic blocks, 308 redirects edges, and then fixes up PHI arguments later in 309 batch. */ 310 SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE); 311 gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION); 312 313 stmt->gimple_phi.nargs++; 314 } 315 } 316 317 /* Adds PHI to BB. */ 318 319 void 320 add_phi_node_to_bb (gimple phi, basic_block bb) 321 { 322 gimple_seq seq = phi_nodes (bb); 323 /* Add the new PHI node to the list of PHI nodes for block BB. */ 324 if (seq == NULL) 325 set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi)); 326 else 327 { 328 gimple_seq_add_stmt (&seq, phi); 329 gcc_assert (seq == phi_nodes (bb)); 330 } 331 332 /* Associate BB to the PHI node. */ 333 gimple_set_bb (phi, bb); 334 335 } 336 337 /* Create a new PHI node for variable VAR at basic block BB. */ 338 339 gimple 340 create_phi_node (tree var, basic_block bb) 341 { 342 gimple phi = make_phi_node (var, EDGE_COUNT (bb->preds)); 343 344 add_phi_node_to_bb (phi, bb); 345 return phi; 346 } 347 348 349 /* Add a new argument to PHI node PHI. DEF is the incoming reaching 350 definition and E is the edge through which DEF reaches PHI. The new 351 argument is added at the end of the argument list. 352 If PHI has reached its maximum capacity, add a few slots. In this case, 353 PHI points to the reallocated phi node when we return. */ 354 355 void 356 add_phi_arg (gimple phi, tree def, edge e, source_location locus) 357 { 358 basic_block bb = e->dest; 359 360 gcc_assert (bb == gimple_bb (phi)); 361 362 /* We resize PHI nodes upon edge creation. We should always have 363 enough room at this point. */ 364 gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi)); 365 366 /* We resize PHI nodes upon edge creation. We should always have 367 enough room at this point. */ 368 gcc_assert (e->dest_idx < gimple_phi_num_args (phi)); 369 370 /* Copy propagation needs to know what object occur in abnormal 371 PHI nodes. This is a convenient place to record such information. */ 372 if (e->flags & EDGE_ABNORMAL) 373 { 374 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1; 375 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1; 376 } 377 378 SET_PHI_ARG_DEF (phi, e->dest_idx, def); 379 gimple_phi_arg_set_location (phi, e->dest_idx, locus); 380 } 381 382 383 /* Remove the Ith argument from PHI's argument list. This routine 384 implements removal by swapping the last alternative with the 385 alternative we want to delete and then shrinking the vector, which 386 is consistent with how we remove an edge from the edge vector. */ 387 388 static void 389 remove_phi_arg_num (gimple phi, int i) 390 { 391 int num_elem = gimple_phi_num_args (phi); 392 393 gcc_assert (i < num_elem); 394 395 /* Delink the item which is being removed. */ 396 delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i)); 397 398 /* If it is not the last element, move the last element 399 to the element we want to delete, resetting all the links. */ 400 if (i != num_elem - 1) 401 { 402 use_operand_p old_p, new_p; 403 old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1); 404 new_p = gimple_phi_arg_imm_use_ptr (phi, i); 405 /* Set use on new node, and link into last element's place. */ 406 *(new_p->use) = *(old_p->use); 407 relink_imm_use (new_p, old_p); 408 /* Move the location as well. */ 409 gimple_phi_arg_set_location (phi, i, 410 gimple_phi_arg_location (phi, num_elem - 1)); 411 } 412 413 /* Shrink the vector and return. Note that we do not have to clear 414 PHI_ARG_DEF because the garbage collector will not look at those 415 elements beyond the first PHI_NUM_ARGS elements of the array. */ 416 phi->gimple_phi.nargs--; 417 } 418 419 420 /* Remove all PHI arguments associated with edge E. */ 421 422 void 423 remove_phi_args (edge e) 424 { 425 gimple_stmt_iterator gsi; 426 427 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) 428 remove_phi_arg_num (gsi_stmt (gsi), e->dest_idx); 429 } 430 431 432 /* Remove the PHI node pointed-to by iterator GSI from basic block BB. After 433 removal, iterator GSI is updated to point to the next PHI node in the 434 sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released 435 into the free pool of SSA names. */ 436 437 void 438 remove_phi_node (gimple_stmt_iterator *gsi, bool release_lhs_p) 439 { 440 gimple phi = gsi_stmt (*gsi); 441 442 if (release_lhs_p) 443 insert_debug_temps_for_defs (gsi); 444 445 gsi_remove (gsi, false); 446 447 /* If we are deleting the PHI node, then we should release the 448 SSA_NAME node so that it can be reused. */ 449 release_phi_node (phi); 450 if (release_lhs_p) 451 release_ssa_name (gimple_phi_result (phi)); 452 } 453 454 /* Remove all the phi nodes from BB. */ 455 456 void 457 remove_phi_nodes (basic_block bb) 458 { 459 gimple_stmt_iterator gsi; 460 461 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); ) 462 remove_phi_node (&gsi, true); 463 464 set_phi_nodes (bb, NULL); 465 } 466 467 #include "gt-tree-phinodes.h" 468