gcc/tree-phinodes.c

   1 /* Generic routines for manipulating PHIs
   2    Copyright (C) 2003-2015 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 "hash-set.h"
  25 #include "machmode.h"
  26 #include "vec.h"
  27 #include "double-int.h"
  28 #include "input.h"
  29 #include "alias.h"
  30 #include "symtab.h"
  31 #include "wide-int.h"
  32 #include "inchash.h"
  33 #include "tree.h"
  34 #include "fold-const.h"
  35 #include "predict.h"
  36 #include "hard-reg-set.h"
  37 #include "input.h"
  38 #include "function.h"
  39 #include "basic-block.h"
  40 #include "tree-ssa-alias.h"
  41 #include "internal-fn.h"
  42 #include "gimple-expr.h"
  43 #include "is-a.h"
  44 #include "gimple.h"
  45 #include "gimple-iterator.h"
  46 #include "gimple-ssa.h"
  47 #include "tree-phinodes.h"
  48 #include "ssa-iterators.h"
  49 #include "stringpool.h"
  50 #include "tree-ssanames.h"
  51 #include "tree-ssa.h"
  52 #include "diagnostic-core.h"
  53
  54 /* Rewriting a function into SSA form can create a huge number of PHIs
  55    many of which may be thrown away shortly after their creation if jumps
  56    were threaded through PHI nodes.
  57
  58    While our garbage collection mechanisms will handle this situation, it
  59    is extremely wasteful to create nodes and throw them away, especially
  60    when the nodes can be reused.
  61
  62    For PR 8361, we can significantly reduce the number of nodes allocated
  63    and thus the total amount of memory allocated by managing PHIs a
  64    little.  This additionally helps reduce the amount of work done by the
  65    garbage collector.  Similar results have been seen on a wider variety
  66    of tests (such as the compiler itself).
  67
  68    PHI nodes have different sizes, so we can't have a single list of all
  69    the PHI nodes as it would be too expensive to walk down that list to
  70    find a PHI of a suitable size.
  71
  72    Instead we have an array of lists of free PHI nodes.  The array is
  73    indexed by the number of PHI alternatives that PHI node can hold.
  74    Except for the last array member, which holds all remaining PHI
  75    nodes.
  76
  77    So to find a free PHI node, we compute its index into the free PHI
  78    node array and see if there are any elements with an exact match.
  79    If so, then we are done.  Otherwise, we test the next larger size
  80    up and continue until we are in the last array element.
  81
  82    We do not actually walk members of the last array element.  While it
  83    might allow us to pick up a few reusable PHI nodes, it could potentially
  84    be very expensive if the program has released a bunch of large PHI nodes,
  85    but keeps asking for even larger PHI nodes.  Experiments have shown that
  86    walking the elements of the last array entry would result in finding less
  87    than .1% additional reusable PHI nodes.
  88
  89    Note that we can never have less than two PHI argument slots.  Thus,
  90    the -2 on all the calculations below.  */
  91
  92 #define NUM_BUCKETS 10
  93 static GTY ((deletable (""))) vec<gimple, va_gc> *free_phinodes[NUM_BUCKETS - 2];
  94 static unsigned long free_phinode_count;
  95
  96 static int ideal_phi_node_len (int);
  97
  98 unsigned int phi_nodes_reused;
  99 unsigned int phi_nodes_created;
 100
 101 /* Dump some simple statistics regarding the re-use of PHI nodes.  */
 102
 103 void
 104 phinodes_print_statistics (void)
 105 {
 106   fprintf (stderr, "PHI nodes allocated: %u\n", phi_nodes_created);
 107   fprintf (stderr, "PHI nodes reused: %u\n", phi_nodes_reused);
 108 }
 109
 110 /* Allocate a PHI node with at least LEN arguments.  If the free list
 111    happens to contain a PHI node with LEN arguments or more, return
 112    that one.  */
 113
 114 static inline gphi *
 115 allocate_phi_node (size_t len)
 116 {
 117   gphi *phi;
 118   size_t bucket = NUM_BUCKETS - 2;
 119   size_t size = sizeof (struct gphi)
 120                 + (len - 1) * sizeof (struct phi_arg_d);
 121
 122   if (free_phinode_count)
 123     for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++)
 124       if (free_phinodes[bucket])
 125         break;
 126
 127   /* If our free list has an element, then use it.  */
 128   if (bucket < NUM_BUCKETS - 2
 129       && gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len)
 130     {
 131       free_phinode_count--;
 132       phi = as_a <gphi *> (free_phinodes[bucket]->pop ());
 133       if (free_phinodes[bucket]->is_empty ())
 134         vec_free (free_phinodes[bucket]);
 135       if (GATHER_STATISTICS)
 136         phi_nodes_reused++;
 137     }
 138   else
 139     {
 140       phi = static_cast <gphi *> (ggc_internal_alloc (size));
 141       if (GATHER_STATISTICS)
 142         {
 143           enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI);
 144           phi_nodes_created++;
 145           gimple_alloc_counts[(int) kind]++;
 146           gimple_alloc_sizes[(int) kind] += size;
 147         }
 148     }
 149
 150   return phi;
 151 }
 152
 153 /* Given LEN, the original number of requested PHI arguments, return
 154    a new, "ideal" length for the PHI node.  The "ideal" length rounds
 155    the total size of the PHI node up to the next power of two bytes.
 156
 157    Rounding up will not result in wasting any memory since the size request
 158    will be rounded up by the GC system anyway.  [ Note this is not entirely
 159    true since the original length might have fit on one of the special
 160    GC pages. ]  By rounding up, we may avoid the need to reallocate the
 161    PHI node later if we increase the number of arguments for the PHI.  */
 162
 163 static int
 164 ideal_phi_node_len (int len)
 165 {
 166   size_t size, new_size;
 167   int log2, new_len;
 168
 169   /* We do not support allocations of less than two PHI argument slots.  */
 170   if (len < 2)
 171     len = 2;
 172
 173   /* Compute the number of bytes of the original request.  */
 174   size = sizeof (struct gphi)
 175          + (len - 1) * sizeof (struct phi_arg_d);
 176
 177   /* Round it up to the next power of two.  */
 178   log2 = ceil_log2 (size);
 179   new_size = 1 << log2;
 180
 181   /* Now compute and return the number of PHI argument slots given an
 182      ideal size allocation.  */
 183   new_len = len + (new_size - size) / sizeof (struct phi_arg_d);
 184   return new_len;
 185 }
 186
 187 /* Return a PHI node with LEN argument slots for variable VAR.  */
 188
 189 static gphi *
 190 make_phi_node (tree var, int len)
 191 {
 192   gphi *phi;
 193   int capacity, i;
 194
 195   capacity = ideal_phi_node_len (len);
 196
 197   phi = allocate_phi_node (capacity);
 198
 199   /* We need to clear the entire PHI node, including the argument
 200      portion, because we represent a "missing PHI argument" by placing
 201      NULL_TREE in PHI_ARG_DEF.  */
 202   memset (phi, 0, (sizeof (struct gphi)
 203                    - sizeof (struct phi_arg_d)
 204                    + sizeof (struct phi_arg_d) * len));
 205   phi->code = GIMPLE_PHI;
 206   gimple_init_singleton (phi);
 207   phi->nargs = len;
 208   phi->capacity = capacity;
 209   if (!var)
 210     ;
 211   else if (TREE_CODE (var) == SSA_NAME)
 212     gimple_phi_set_result (phi, var);
 213   else
 214     gimple_phi_set_result (phi, make_ssa_name (var, phi));
 215
 216   for (i = 0; i < capacity; i++)
 217     {
 218       use_operand_p  imm;
 219
 220       gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION);
 221       imm = gimple_phi_arg_imm_use_ptr (phi, i);
 222       imm->use = gimple_phi_arg_def_ptr (phi, i);
 223       imm->prev = NULL;
 224       imm->next = NULL;
 225       imm->loc.stmt = phi;
 226     }
 227
 228   return phi;
 229 }
 230
 231 /* We no longer need PHI, release it so that it may be reused.  */
 232
 233 void
 234 release_phi_node (gimple phi)
 235 {
 236   size_t bucket;
 237   size_t len = gimple_phi_capacity (phi);
 238   size_t x;
 239
 240   for (x = 0; x < gimple_phi_num_args (phi); x++)
 241     {
 242       use_operand_p  imm;
 243       imm = gimple_phi_arg_imm_use_ptr (phi, x);
 244       delink_imm_use (imm);
 245     }
 246
 247   bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len;
 248   bucket -= 2;
 249   vec_safe_push (free_phinodes[bucket], phi);
 250   free_phinode_count++;
 251 }
 252
 253
 254 /* Resize an existing PHI node.  The only way is up.  Return the
 255    possibly relocated phi.  */
 256
 257 static gphi *
 258 resize_phi_node (gphi *phi, size_t len)
 259 {
 260   size_t old_size, i;
 261   gphi *new_phi;
 262
 263   gcc_assert (len > gimple_phi_capacity (phi));
 264
 265   /* The garbage collector will not look at the PHI node beyond the
 266      first PHI_NUM_ARGS elements.  Therefore, all we have to copy is a
 267      portion of the PHI node currently in use.  */
 268   old_size = sizeof (struct gphi)
 269              + (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d);
 270
 271   new_phi = allocate_phi_node (len);
 272
 273   memcpy (new_phi, phi, old_size);
 274
 275   for (i = 0; i < gimple_phi_num_args (new_phi); i++)
 276     {
 277       use_operand_p imm, old_imm;
 278       imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
 279       old_imm = gimple_phi_arg_imm_use_ptr (phi, i);
 280       imm->use = gimple_phi_arg_def_ptr (new_phi, i);
 281       relink_imm_use_stmt (imm, old_imm, new_phi);
 282     }
 283
 284   new_phi->capacity = len;
 285
 286   for (i = gimple_phi_num_args (new_phi); i < len; i++)
 287     {
 288       use_operand_p imm;
 289
 290       gimple_phi_arg_set_location (new_phi, i, UNKNOWN_LOCATION);
 291       imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
 292       imm->use = gimple_phi_arg_def_ptr (new_phi, i);
 293       imm->prev = NULL;
 294       imm->next = NULL;
 295       imm->loc.stmt = new_phi;
 296     }
 297
 298   return new_phi;
 299 }
 300
 301 /* Reserve PHI arguments for a new edge to basic block BB.  */
 302
 303 void
 304 reserve_phi_args_for_new_edge (basic_block bb)
 305 {
 306   size_t len = EDGE_COUNT (bb->preds);
 307   size_t cap = ideal_phi_node_len (len + 4);
 308   gphi_iterator gsi;
 309
 310   for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 311     {
 312       gphi *stmt = gsi.phi ();
 313
 314       if (len > gimple_phi_capacity (stmt))
 315         {
 316           gphi *new_phi = resize_phi_node (stmt, cap);
 317
 318           /* The result of the PHI is defined by this PHI node.  */
 319           SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi;
 320           gsi_set_stmt (&gsi, new_phi);
 321
 322           release_phi_node (stmt);
 323           stmt = new_phi;
 324         }
 325
 326       /* We represent a "missing PHI argument" by placing NULL_TREE in
 327          the corresponding slot.  If PHI arguments were added
 328          immediately after an edge is created, this zeroing would not
 329          be necessary, but unfortunately this is not the case.  For
 330          example, the loop optimizer duplicates several basic blocks,
 331          redirects edges, and then fixes up PHI arguments later in
 332          batch.  */
 333       SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE);
 334       gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION);
 335
 336       stmt->nargs++;
 337     }
 338 }
 339
 340 /* Adds PHI to BB.  */
 341
 342 void
 343 add_phi_node_to_bb (gphi *phi, basic_block bb)
 344 {
 345   gimple_seq seq = phi_nodes (bb);
 346   /* Add the new PHI node to the list of PHI nodes for block BB.  */
 347   if (seq == NULL)
 348     set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi));
 349   else
 350     {
 351       gimple_seq_add_stmt (&seq, phi);
 352       gcc_assert (seq == phi_nodes (bb));
 353     }
 354
 355   /* Associate BB to the PHI node.  */
 356   gimple_set_bb (phi, bb);
 357
 358 }
 359
 360 /* Create a new PHI node for variable VAR at basic block BB.  */
 361
 362 gphi *
 363 create_phi_node (tree var, basic_block bb)
 364 {
 365   gphi *phi = make_phi_node (var, EDGE_COUNT (bb->preds));
 366
 367   add_phi_node_to_bb (phi, bb);
 368   return phi;
 369 }
 370
 371
 372 /* Add a new argument to PHI node PHI.  DEF is the incoming reaching
 373    definition and E is the edge through which DEF reaches PHI.  The new
 374    argument is added at the end of the argument list.
 375    If PHI has reached its maximum capacity, add a few slots.  In this case,
 376    PHI points to the reallocated phi node when we return.  */
 377
 378 void
 379 add_phi_arg (gphi *phi, tree def, edge e, source_location locus)
 380 {
 381   basic_block bb = e->dest;
 382
 383   gcc_assert (bb == gimple_bb (phi));
 384
 385   /* We resize PHI nodes upon edge creation.  We should always have
 386      enough room at this point.  */
 387   gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi));
 388
 389   /* We resize PHI nodes upon edge creation.  We should always have
 390      enough room at this point.  */
 391   gcc_assert (e->dest_idx < gimple_phi_num_args (phi));
 392
 393   /* Copy propagation needs to know what object occur in abnormal
 394      PHI nodes.  This is a convenient place to record such information.  */
 395   if (e->flags & EDGE_ABNORMAL)
 396     {
 397       SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1;
 398       SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1;
 399     }
 400
 401   SET_PHI_ARG_DEF (phi, e->dest_idx, def);
 402   gimple_phi_arg_set_location (phi, e->dest_idx, locus);
 403 }
 404
 405
 406 /* Remove the Ith argument from PHI's argument list.  This routine
 407    implements removal by swapping the last alternative with the
 408    alternative we want to delete and then shrinking the vector, which
 409    is consistent with how we remove an edge from the edge vector.  */
 410
 411 static void
 412 remove_phi_arg_num (gphi *phi, int i)
 413 {
 414   int num_elem = gimple_phi_num_args (phi);
 415
 416   gcc_assert (i < num_elem);
 417
 418   /* Delink the item which is being removed.  */
 419   delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i));
 420
 421   /* If it is not the last element, move the last element
 422      to the element we want to delete, resetting all the links. */
 423   if (i != num_elem - 1)
 424     {
 425       use_operand_p old_p, new_p;
 426       old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1);
 427       new_p = gimple_phi_arg_imm_use_ptr (phi, i);
 428       /* Set use on new node, and link into last element's place.  */
 429       *(new_p->use) = *(old_p->use);
 430       relink_imm_use (new_p, old_p);
 431       /* Move the location as well.  */
 432       gimple_phi_arg_set_location (phi, i,
 433                                    gimple_phi_arg_location (phi, num_elem - 1));
 434     }
 435
 436   /* Shrink the vector and return.  Note that we do not have to clear
 437      PHI_ARG_DEF because the garbage collector will not look at those
 438      elements beyond the first PHI_NUM_ARGS elements of the array.  */
 439   phi->nargs--;
 440 }
 441
 442
 443 /* Remove all PHI arguments associated with edge E.  */
 444
 445 void
 446 remove_phi_args (edge e)
 447 {
 448   gphi_iterator gsi;
 449
 450   for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
 451     remove_phi_arg_num (gsi.phi (),
 452                         e->dest_idx);
 453 }
 454
 455
 456 /* Remove the PHI node pointed-to by iterator GSI from basic block BB.  After
 457    removal, iterator GSI is updated to point to the next PHI node in the
 458    sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released
 459    into the free pool of SSA names.  */
 460
 461 void
 462 remove_phi_node (gimple_stmt_iterator *gsi, bool release_lhs_p)
 463 {
 464   gimple phi = gsi_stmt (*gsi);
 465
 466   if (release_lhs_p)
 467     insert_debug_temps_for_defs (gsi);
 468
 469   gsi_remove (gsi, false);
 470
 471   /* If we are deleting the PHI node, then we should release the
 472      SSA_NAME node so that it can be reused.  */
 473   release_phi_node (phi);
 474   if (release_lhs_p)
 475     release_ssa_name (gimple_phi_result (phi));
 476 }
 477
 478 /* Remove all the phi nodes from BB.  */
 479
 480 void
 481 remove_phi_nodes (basic_block bb)
 482 {
 483   gphi_iterator gsi;
 484
 485   for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); )
 486     remove_phi_node (&gsi, true);
 487
 488   set_phi_nodes (bb, NULL);
 489 }
 490
 491 /* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
 492    NULL.  */
 493
 494 tree
 495 degenerate_phi_result (gphi *phi)
 496 {
 497   tree lhs = gimple_phi_result (phi);
 498   tree val = NULL;
 499   size_t i;
 500
 501   /* Ignoring arguments which are the same as LHS, if all the remaining
 502      arguments are the same, then the PHI is a degenerate and has the
 503      value of that common argument.  */
 504   for (i = 0; i < gimple_phi_num_args (phi); i++)
 505     {
 506       tree arg = gimple_phi_arg_def (phi, i);
 507
 508       if (arg == lhs)
 509         continue;
 510       else if (!arg)
 511         break;
 512       else if (!val)
 513         val = arg;
 514       else if (arg == val)
 515         continue;
 516       /* We bring in some of operand_equal_p not only to speed things
 517          up, but also to avoid crashing when dereferencing the type of
 518          a released SSA name.  */
 519       else if (TREE_CODE (val) != TREE_CODE (arg)
 520                || TREE_CODE (val) == SSA_NAME
 521                || !operand_equal_p (arg, val, 0))
 522         break;
 523     }
 524   return (i == gimple_phi_num_args (phi) ? val : NULL);
 525 }
 526
 527 /* Set PHI nodes of a basic block BB to SEQ.  */
 528
 529 void
 530 set_phi_nodes (basic_block bb, gimple_seq seq)
 531 {
 532   gimple_stmt_iterator i;
 533
 534   gcc_checking_assert (!(bb->flags & BB_RTL));
 535   bb->il.gimple.phi_nodes = seq;
 536   if (seq)
 537     for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i))
 538       gimple_set_bb (gsi_stmt (i), bb);
 539 }
 540
 541 #include "gt-tree-phinodes.h"