1/* Generic routines for manipulating PHIs 2 Copyright (C) 2003-2020 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify 7it under the terms of the GNU General Public License as published by 8the Free Software Foundation; either version 3, or (at your option) 9any later version. 10 11GCC is distributed in the hope that it will be useful, 12but WITHOUT ANY WARRANTY; without even the implied warranty of 13MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14GNU General Public License for more details. 15 16You should have received a copy of the GNU General Public License 17along 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 "backend.h" 24#include "tree.h" 25#include "gimple.h" 26#include "ssa.h" 27#include "fold-const.h" 28#include "gimple-iterator.h" 29#include "tree-ssa.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 70static GTY ((deletable (""))) vec<gimple *, va_gc> *free_phinodes[NUM_BUCKETS - 2]; 71static unsigned long free_phinode_count; 72 73static int ideal_phi_node_len (int); 74 75unsigned int phi_nodes_reused; 76unsigned int phi_nodes_created; 77 78/* Dump some simple statistics regarding the re-use of PHI nodes. */ 79 80void 81phinodes_print_statistics (void) 82{ 83 fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes allocated:", 84 SIZE_AMOUNT (phi_nodes_created)); 85 fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes reused:", 86 SIZE_AMOUNT (phi_nodes_reused)); 87} 88 89/* Allocate a PHI node with at least LEN arguments. If the free list 90 happens to contain a PHI node with LEN arguments or more, return 91 that one. */ 92 93static inline gphi * 94allocate_phi_node (size_t len) 95{ 96 gphi *phi; 97 size_t bucket = NUM_BUCKETS - 2; 98 size_t size = sizeof (struct gphi) 99 + (len - 1) * sizeof (struct phi_arg_d); 100 101 if (free_phinode_count) 102 for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++) 103 if (free_phinodes[bucket]) 104 break; 105 106 /* If our free list has an element, then use it. */ 107 if (bucket < NUM_BUCKETS - 2 108 && gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len) 109 { 110 free_phinode_count--; 111 phi = as_a <gphi *> (free_phinodes[bucket]->pop ()); 112 if (free_phinodes[bucket]->is_empty ()) 113 vec_free (free_phinodes[bucket]); 114 if (GATHER_STATISTICS) 115 phi_nodes_reused++; 116 } 117 else 118 { 119 phi = static_cast <gphi *> (ggc_internal_alloc (size)); 120 if (GATHER_STATISTICS) 121 { 122 enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI); 123 phi_nodes_created++; 124 gimple_alloc_counts[(int) kind]++; 125 gimple_alloc_sizes[(int) kind] += size; 126 } 127 } 128 129 return phi; 130} 131 132/* Given LEN, the original number of requested PHI arguments, return 133 a new, "ideal" length for the PHI node. The "ideal" length rounds 134 the total size of the PHI node up to the next power of two bytes. 135 136 Rounding up will not result in wasting any memory since the size request 137 will be rounded up by the GC system anyway. [ Note this is not entirely 138 true since the original length might have fit on one of the special 139 GC pages. ] By rounding up, we may avoid the need to reallocate the 140 PHI node later if we increase the number of arguments for the PHI. */ 141 142static int 143ideal_phi_node_len (int len) 144{ 145 size_t size, new_size; 146 int log2, new_len; 147 148 /* We do not support allocations of less than two PHI argument slots. */ 149 if (len < 2) 150 len = 2; 151 152 /* Compute the number of bytes of the original request. */ 153 size = sizeof (struct gphi) 154 + (len - 1) * sizeof (struct phi_arg_d); 155 156 /* Round it up to the next power of two. */ 157 log2 = ceil_log2 (size); 158 new_size = 1 << log2; 159 160 /* Now compute and return the number of PHI argument slots given an 161 ideal size allocation. */ 162 new_len = len + (new_size - size) / sizeof (struct phi_arg_d); 163 return new_len; 164} 165 166/* Return a PHI node with LEN argument slots for variable VAR. */ 167 168static gphi * 169make_phi_node (tree var, int len) 170{ 171 gphi *phi; 172 int capacity, i; 173 174 capacity = ideal_phi_node_len (len); 175 176 phi = allocate_phi_node (capacity); 177 178 /* We need to clear the entire PHI node, including the argument 179 portion, because we represent a "missing PHI argument" by placing 180 NULL_TREE in PHI_ARG_DEF. */ 181 memset (phi, 0, (sizeof (struct gphi) 182 - sizeof (struct phi_arg_d) 183 + sizeof (struct phi_arg_d) * len)); 184 phi->code = GIMPLE_PHI; 185 gimple_init_singleton (phi); 186 phi->nargs = len; 187 phi->capacity = capacity; 188 if (!var) 189 ; 190 else if (TREE_CODE (var) == SSA_NAME) 191 gimple_phi_set_result (phi, var); 192 else 193 gimple_phi_set_result (phi, make_ssa_name (var, phi)); 194 195 for (i = 0; i < len; i++) 196 { 197 use_operand_p imm; 198 199 gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION); 200 imm = gimple_phi_arg_imm_use_ptr (phi, i); 201 imm->use = gimple_phi_arg_def_ptr (phi, i); 202 imm->prev = NULL; 203 imm->next = NULL; 204 imm->loc.stmt = phi; 205 } 206 207 return phi; 208} 209 210/* We no longer need PHI, release it so that it may be reused. */ 211 212static void 213release_phi_node (gimple *phi) 214{ 215 size_t bucket; 216 size_t len = gimple_phi_capacity (phi); 217 size_t x; 218 219 for (x = 0; x < gimple_phi_num_args (phi); x++) 220 { 221 use_operand_p imm; 222 imm = gimple_phi_arg_imm_use_ptr (phi, x); 223 delink_imm_use (imm); 224 } 225 226 bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len; 227 bucket -= 2; 228 vec_safe_push (free_phinodes[bucket], phi); 229 free_phinode_count++; 230} 231 232 233/* Resize an existing PHI node. The only way is up. Return the 234 possibly relocated phi. */ 235 236static gphi * 237resize_phi_node (gphi *phi, size_t len) 238{ 239 size_t old_size, i; 240 gphi *new_phi; 241 242 gcc_assert (len > gimple_phi_capacity (phi)); 243 244 /* The garbage collector will not look at the PHI node beyond the 245 first PHI_NUM_ARGS elements. Therefore, all we have to copy is a 246 portion of the PHI node currently in use. */ 247 old_size = sizeof (struct gphi) 248 + (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d); 249 250 new_phi = allocate_phi_node (len); 251 252 memcpy (new_phi, phi, old_size); 253 memset ((char *)new_phi + old_size, 0, 254 (sizeof (struct gphi) 255 - sizeof (struct phi_arg_d) 256 + sizeof (struct phi_arg_d) * len) - old_size); 257 258 for (i = 0; i < gimple_phi_num_args (new_phi); i++) 259 { 260 use_operand_p imm, old_imm; 261 imm = gimple_phi_arg_imm_use_ptr (new_phi, i); 262 old_imm = gimple_phi_arg_imm_use_ptr (phi, i); 263 imm->use = gimple_phi_arg_def_ptr (new_phi, i); 264 relink_imm_use_stmt (imm, old_imm, new_phi); 265 } 266 267 new_phi->capacity = len; 268 269 return new_phi; 270} 271 272/* Reserve PHI arguments for a new edge to basic block BB. */ 273 274void 275reserve_phi_args_for_new_edge (basic_block bb) 276{ 277 size_t len = EDGE_COUNT (bb->preds); 278 size_t cap = ideal_phi_node_len (len + 4); 279 gphi_iterator gsi; 280 281 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 282 { 283 gphi *stmt = gsi.phi (); 284 285 if (len > gimple_phi_capacity (stmt)) 286 { 287 gphi *new_phi = resize_phi_node (stmt, cap); 288 289 /* The result of the PHI is defined by this PHI node. */ 290 SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi; 291 gsi_set_stmt (&gsi, new_phi); 292 293 release_phi_node (stmt); 294 stmt = new_phi; 295 } 296 297 stmt->nargs++; 298 299 /* We represent a "missing PHI argument" by placing NULL_TREE in 300 the corresponding slot. If PHI arguments were added 301 immediately after an edge is created, this zeroing would not 302 be necessary, but unfortunately this is not the case. For 303 example, the loop optimizer duplicates several basic blocks, 304 redirects edges, and then fixes up PHI arguments later in 305 batch. */ 306 use_operand_p imm = gimple_phi_arg_imm_use_ptr (stmt, len - 1); 307 imm->use = gimple_phi_arg_def_ptr (stmt, len - 1); 308 imm->prev = NULL; 309 imm->next = NULL; 310 imm->loc.stmt = stmt; 311 SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE); 312 gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION); 313 } 314} 315 316/* Adds PHI to BB. */ 317 318void 319add_phi_node_to_bb (gphi *phi, basic_block bb) 320{ 321 gimple_seq seq = phi_nodes (bb); 322 /* Add the new PHI node to the list of PHI nodes for block BB. */ 323 if (seq == NULL) 324 set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi)); 325 else 326 { 327 gimple_seq_add_stmt (&seq, phi); 328 gcc_assert (seq == phi_nodes (bb)); 329 } 330 331 /* Associate BB to the PHI node. */ 332 gimple_set_bb (phi, bb); 333 334} 335 336/* Create a new PHI node for variable VAR at basic block BB. */ 337 338gphi * 339create_phi_node (tree var, basic_block bb) 340{ 341 gphi *phi = make_phi_node (var, EDGE_COUNT (bb->preds)); 342 343 add_phi_node_to_bb (phi, bb); 344 return phi; 345} 346 347 348/* Add a new argument to PHI node PHI. DEF is the incoming reaching 349 definition and E is the edge through which DEF reaches PHI. The new 350 argument is added at the end of the argument list. 351 If PHI has reached its maximum capacity, add a few slots. In this case, 352 PHI points to the reallocated phi node when we return. */ 353 354void 355add_phi_arg (gphi *phi, tree def, edge e, location_t locus) 356{ 357 basic_block bb = e->dest; 358 359 gcc_assert (bb == gimple_bb (phi)); 360 361 /* We resize PHI nodes upon edge creation. We should always have 362 enough room at this point. */ 363 gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi)); 364 365 /* We resize PHI nodes upon edge creation. We should always have 366 enough room at this point. */ 367 gcc_assert (e->dest_idx < gimple_phi_num_args (phi)); 368 369 /* Copy propagation needs to know what object occur in abnormal 370 PHI nodes. This is a convenient place to record such information. */ 371 if (e->flags & EDGE_ABNORMAL) 372 { 373 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1; 374 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1; 375 } 376 377 SET_PHI_ARG_DEF (phi, e->dest_idx, def); 378 gimple_phi_arg_set_location (phi, e->dest_idx, locus); 379} 380 381 382/* Remove the Ith argument from PHI's argument list. This routine 383 implements removal by swapping the last alternative with the 384 alternative we want to delete and then shrinking the vector, which 385 is consistent with how we remove an edge from the edge vector. */ 386 387static void 388remove_phi_arg_num (gphi *phi, int i) 389{ 390 int num_elem = gimple_phi_num_args (phi); 391 392 gcc_assert (i < num_elem); 393 394 /* Delink the item which is being removed. */ 395 delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i)); 396 397 /* If it is not the last element, move the last element 398 to the element we want to delete, resetting all the links. */ 399 if (i != num_elem - 1) 400 { 401 use_operand_p old_p, new_p; 402 old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1); 403 new_p = gimple_phi_arg_imm_use_ptr (phi, i); 404 /* Set use on new node, and link into last element's place. */ 405 *(new_p->use) = *(old_p->use); 406 relink_imm_use (new_p, old_p); 407 /* Move the location as well. */ 408 gimple_phi_arg_set_location (phi, i, 409 gimple_phi_arg_location (phi, num_elem - 1)); 410 } 411 412 /* Shrink the vector and return. Note that we do not have to clear 413 PHI_ARG_DEF because the garbage collector will not look at those 414 elements beyond the first PHI_NUM_ARGS elements of the array. */ 415 phi->nargs--; 416} 417 418 419/* Remove all PHI arguments associated with edge E. */ 420 421void 422remove_phi_args (edge e) 423{ 424 gphi_iterator gsi; 425 426 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) 427 remove_phi_arg_num (gsi.phi (), 428 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 437void 438remove_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 456void 457remove_phi_nodes (basic_block bb) 458{ 459 gphi_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/* Given PHI, return its RHS if the PHI is a degenerate, otherwise return 468 NULL. */ 469 470tree 471degenerate_phi_result (gphi *phi) 472{ 473 tree lhs = gimple_phi_result (phi); 474 tree val = NULL; 475 size_t i; 476 477 /* Ignoring arguments which are the same as LHS, if all the remaining 478 arguments are the same, then the PHI is a degenerate and has the 479 value of that common argument. */ 480 for (i = 0; i < gimple_phi_num_args (phi); i++) 481 { 482 tree arg = gimple_phi_arg_def (phi, i); 483 484 if (arg == lhs) 485 continue; 486 else if (!arg) 487 break; 488 else if (!val) 489 val = arg; 490 else if (arg == val) 491 continue; 492 /* We bring in some of operand_equal_p not only to speed things 493 up, but also to avoid crashing when dereferencing the type of 494 a released SSA name. */ 495 else if (TREE_CODE (val) != TREE_CODE (arg) 496 || TREE_CODE (val) == SSA_NAME 497 || !operand_equal_p (arg, val, 0)) 498 break; 499 } 500 return (i == gimple_phi_num_args (phi) ? val : NULL); 501} 502 503/* Set PHI nodes of a basic block BB to SEQ. */ 504 505void 506set_phi_nodes (basic_block bb, gimple_seq seq) 507{ 508 gimple_stmt_iterator i; 509 510 gcc_checking_assert (!(bb->flags & BB_RTL)); 511 bb->il.gimple.phi_nodes = seq; 512 if (seq) 513 for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i)) 514 gimple_set_bb (gsi_stmt (i), bb); 515} 516 517#include "gt-tree-phinodes.h" 518