gcc/ipa-icf.h

   1 /* Interprocedural semantic function equality pass
   2    Copyright (C) 2014-2022 Free Software Foundation, Inc.
   3
   4    Contributed by Jan Hubicka <hubicka@ucw.cz> and Martin Liska <mliska@suse.cz>
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING3.  If not see
  20 <http://www.gnu.org/licenses/>.  */
  21
  22 namespace ipa_icf {
  23 class sem_item;
  24
  25 /* Congruence class encompasses a collection of either functions or
  26    read-only variables. These items are considered to be equivalent
  27    if not proved the opposite.  */
  28 class congruence_class
  29 {
  30 public:
  31   /* Congruence class constructor for a new class with _ID.  */
  32   congruence_class (unsigned int _id): in_worklist (false), id (_id),
  33   referenced_by_count (0)
  34   {
  35   }
  36
  37   /* Destructor.  */
  38   ~congruence_class ()
  39   {
  40   }
  41
  42   /* Dump function prints all class members to a FILE with an INDENT.  */
  43   void dump (FILE *file, unsigned int indent = 0) const;
  44
  45   /* Returns true if there's a member that is used from another group.  */
  46   bool is_class_used (void);
  47
  48   /* Flag is used in case we want to remove a class from worklist and
  49      delete operation is quite expensive for
  50      the data structure (linked list).  */
  51   bool in_worklist;
  52
  53   /* Vector of all group members.  */
  54   auto_vec <sem_item *> members;
  55
  56   /* Global unique class identifier.  */
  57   unsigned int id;
  58
  59   /* Total number of references to items of this class.  */
  60   unsigned referenced_by_count;
  61 };
  62
  63 /* Semantic item type enum.  */
  64 enum sem_item_type
  65 {
  66   FUNC,
  67   VAR
  68 };
  69
  70 /* Class is container for address references for a symtab_node.  */
  71
  72 class symbol_compare_collection
  73 {
  74 public:
  75   /* Constructor.  */
  76   symbol_compare_collection (symtab_node *node);
  77
  78   /* Destructor.  */
  79   ~symbol_compare_collection ()
  80   {
  81     m_references.release ();
  82     m_interposables.release ();
  83   }
  84
  85   /* Vector of address references.  */
  86   vec<symtab_node *> m_references;
  87
  88   /* Vector of interposable references.  */
  89   vec<symtab_node *> m_interposables;
  90 };
  91
  92 /* Hash traits for symbol_compare_collection map.  */
  93
  94 struct symbol_compare_hash : nofree_ptr_hash <symbol_compare_collection>
  95 {
  96   static hashval_t
  97   hash (value_type v)
  98   {
  99     inchash::hash hstate;
 100     hstate.add_int (v->m_references.length ());
 101
 102     for (unsigned i = 0; i < v->m_references.length (); i++)
 103       hstate.add_int (v->m_references[i]->ultimate_alias_target ()->order);
 104
 105     hstate.add_int (v->m_interposables.length ());
 106
 107     for (unsigned i = 0; i < v->m_interposables.length (); i++)
 108       hstate.add_int (v->m_interposables[i]->ultimate_alias_target ()->order);
 109
 110     return hstate.end ();
 111   }
 112
 113   static bool
 114   equal (value_type a, value_type b)
 115   {
 116     if (a->m_references.length () != b->m_references.length ()
 117         || a->m_interposables.length () != b->m_interposables.length ())
 118       return false;
 119
 120     for (unsigned i = 0; i < a->m_references.length (); i++)
 121       if (a->m_references[i]->equal_address_to (b->m_references[i]) != 1)
 122         return false;
 123
 124     for (unsigned i = 0; i < a->m_interposables.length (); i++)
 125       if (!a->m_interposables[i]->semantically_equivalent_p
 126         (b->m_interposables[i]))
 127         return false;
 128
 129     return true;
 130   }
 131 };
 132
 133 /* Semantic item usage pair.  */
 134 class sem_usage_pair
 135 {
 136 public:
 137   /* Constructor for key value pair, where _ITEM is key and _INDEX is a target.  */
 138   sem_usage_pair (sem_item *_item, unsigned int _index);
 139
 140   /* Target semantic item where an item is used.  */
 141   sem_item *item;
 142
 143   /* Index of usage of such an item.  */
 144   unsigned int index;
 145 };
 146
 147 struct sem_usage_pair_hash : pointer_hash <sem_usage_pair>
 148 {
 149   static inline hashval_t hash (sem_usage_pair *);
 150   static inline bool equal (sem_usage_pair *, sem_usage_pair *);
 151 };
 152
 153 inline hashval_t
 154 sem_usage_pair_hash::hash (sem_usage_pair *pair)
 155 {
 156   inchash::hash hstate;
 157
 158   hstate.add_ptr (pair->item);
 159   hstate.add_int (pair->index);
 160
 161   return hstate.end ();
 162 }
 163
 164 inline bool
 165 sem_usage_pair_hash::equal (sem_usage_pair *p1, sem_usage_pair *p2)
 166 {
 167   return p1->item == p2->item && p1->index == p2->index;
 168 }
 169
 170 struct sem_usage_hash : sem_usage_pair_hash, typed_delete_remove <sem_usage_pair> {};
 171 typedef hash_map<sem_usage_hash, auto_vec<sem_item *> > ref_map;
 172
 173 typedef std::pair<symtab_node *, symtab_node *> symtab_pair;
 174
 175 /* Semantic item is a base class that encapsulates all shared functionality
 176    for both semantic function and variable items.  */
 177 class sem_item
 178 {
 179 public:
 180   /* Semantic item constructor for a node of _TYPE, where STACK is used
 181      for bitmap memory allocation.  */
 182   sem_item (sem_item_type _type, bitmap_obstack *stack);
 183
 184   /* Semantic item constructor for a node of _TYPE, where STACK is used
 185      for bitmap memory allocation.  The item is based on symtab node _NODE.  */
 186   sem_item (sem_item_type _type, symtab_node *_node, bitmap_obstack *stack);
 187
 188   virtual ~sem_item ();
 189
 190   /* Dump function for debugging purpose.  */
 191   DEBUG_FUNCTION void dump (void);
 192
 193   /* Semantic item initialization function.  */
 194   virtual void init (ipa_icf_gimple::func_checker *) = 0;
 195
 196   /* Add reference to a semantic TARGET.  */
 197   void add_reference (ref_map *map, sem_item *target);
 198
 199   /* Fast equality function based on knowledge known in WPA.  */
 200   virtual bool equals_wpa (sem_item *item,
 201                            hash_map <symtab_node *, sem_item *> &ignored_nodes) = 0;
 202
 203   /* Returns true if the item equals to ITEM given as argument.  */
 204   virtual bool equals (sem_item *item,
 205                        hash_map <symtab_node *, sem_item *> &ignored_nodes) = 0;
 206
 207   /* References independent hash function.  */
 208   virtual hashval_t get_hash (void) = 0;
 209
 210   /* Set new hash value of the item.  */
 211   void set_hash (hashval_t hash);
 212
 213   /* Merges instance with an ALIAS_ITEM, where alias, thunk or redirection can
 214      be applied.  */
 215   virtual bool merge (sem_item *alias_item) = 0;
 216
 217   /* Dump symbol to FILE.  */
 218   virtual void dump_to_file (FILE *file) = 0;
 219
 220   /* Update hash by address sensitive references.  */
 221   void update_hash_by_addr_refs (hash_map <symtab_node *,
 222                                  sem_item *> &m_symtab_node_map);
 223
 224   /* Update hash by computed local hash values taken from different
 225      semantic items.  */
 226   void update_hash_by_local_refs (hash_map <symtab_node *,
 227                                   sem_item *> &m_symtab_node_map);
 228
 229   /* Return base tree that can be used for compatible_types_p and
 230      contains_polymorphic_type_p comparison.  */
 231   static bool get_base_types (tree *t1, tree *t2);
 232
 233   /* Return true if target supports alias symbols.  */
 234   bool target_supports_symbol_aliases_p (void);
 235
 236   /* Item type.  */
 237   sem_item_type type;
 238
 239   /* Symtab node.  */
 240   symtab_node *node;
 241
 242   /* Declaration tree node.  */
 243   tree decl;
 244
 245   /* Number of references to a semantic symbols (function calls,
 246      variable references).  */
 247   unsigned reference_count;
 248
 249   /* Pointer to a congruence class the item belongs to.  */
 250   congruence_class *cls;
 251
 252   /* Index of the item in a class belonging to.  */
 253   unsigned int index_in_class;
 254
 255   /* A bitmap with indices of all classes referencing this item.  */
 256   bitmap usage_index_bitmap;
 257
 258   /* List of tree references (either FUNC_DECL or VAR_DECL).  */
 259   vec <tree> tree_refs;
 260
 261   /* A set with symbol table references.  */
 262   hash_set <symtab_node *> refs_set;
 263
 264   /* Temporary hash used where hash values of references are added.  */
 265   hashval_t global_hash;
 266
 267   /* Number of references to this symbol.  */
 268   unsigned referenced_by_count;
 269 protected:
 270   /* Cached, once calculated hash for the item.  */
 271
 272   /* Compare properties of symbol that does not affect semantics of symbol
 273      itself but affects semantics of its references.
 274      If ADDRESS is true, do extra checking needed for IPA_REF_ADDR.  */
 275   static bool compare_referenced_symbol_properties (symtab_node *used_by,
 276                                                     symtab_node *n1,
 277                                                     symtab_node *n2,
 278                                                     bool address);
 279
 280   /* Hash properties compared by compare_referenced_symbol_properties.  */
 281   void hash_referenced_symbol_properties (symtab_node *ref,
 282                                           inchash::hash &hstate,
 283                                           bool address);
 284
 285   /* For a given symbol table nodes N1 and N2, we check that FUNCTION_DECLs
 286      point to a same function. Comparison can be skipped if IGNORED_NODES
 287      contains these nodes.  ADDRESS indicate if address is taken.  */
 288   bool compare_symbol_references (hash_map <symtab_node *, sem_item *>
 289                                   &ignored_nodes,
 290                                   symtab_node *n1, symtab_node *n2,
 291                                   bool address);
 292 protected:
 293   /* Hash of item.  */
 294   hashval_t m_hash;
 295
 296   /* Indicated whether a hash value has been set or not.  */
 297   bool m_hash_set;
 298
 299 private:
 300   /* Initialize internal data structures. Bitmap STACK is used for
 301      bitmap memory allocation process.  */
 302   void setup (bitmap_obstack *stack);
 303
 304   /* Because types can be arbitrarily large, avoid quadratic bottleneck.  */
 305   static hash_map<const_tree, hashval_t> m_type_hash_cache;
 306 }; // class sem_item
 307
 308 class sem_function: public sem_item
 309 {
 310 public:
 311   /* Semantic function constructor that uses STACK as bitmap memory stack.  */
 312   sem_function (bitmap_obstack *stack);
 313
 314   /*  Constructor based on callgraph node _NODE.
 315       Bitmap STACK is used for memory allocation.  */
 316   sem_function (cgraph_node *_node, bitmap_obstack *stack);
 317
 318   ~sem_function ();
 319
 320   virtual void init (ipa_icf_gimple::func_checker *);
 321   virtual bool equals_wpa (sem_item *item,
 322                            hash_map <symtab_node *, sem_item *> &ignored_nodes);
 323   virtual hashval_t get_hash (void);
 324   virtual bool equals (sem_item *item,
 325                        hash_map <symtab_node *, sem_item *> &ignored_nodes);
 326   virtual bool merge (sem_item *alias_item);
 327
 328   /* Dump symbol to FILE.  */
 329   virtual void dump_to_file (FILE *file)
 330   {
 331     gcc_assert (file);
 332     dump_function_to_file (decl, file, TDF_DETAILS);
 333   }
 334
 335   /* Returns cgraph_node.  */
 336   inline cgraph_node *get_node (void)
 337   {
 338     return dyn_cast <cgraph_node *> (node);
 339   }
 340
 341   /* Improve accumulated hash for HSTATE based on a gimple statement STMT.  */
 342   void hash_stmt (gimple *stmt, inchash::hash &inchash);
 343
 344   /* Return true if polymorphic comparison must be processed.  */
 345   bool compare_polymorphic_p (void);
 346
 347   /* For a given call graph NODE, the function constructs new
 348      semantic function item.  */
 349   static sem_function *parse (cgraph_node *node, bitmap_obstack *stack,
 350                               ipa_icf_gimple::func_checker *checker);
 351
 352   /* Perform additional checks needed to match types of used function
 353      parameters.  */
 354   bool compatible_parm_types_p (tree, tree);
 355
 356   /* Exception handling region tree.  */
 357   eh_region region_tree;
 358
 359   /* Number of function arguments.  */
 360   unsigned int arg_count;
 361
 362   /* Total amount of edges in the function.  */
 363   unsigned int edge_count;
 364
 365   /* Vector of sizes of all basic blocks.  */
 366   vec <unsigned int> bb_sizes;
 367
 368   /* Control flow graph checksum.  */
 369   hashval_t cfg_checksum;
 370
 371   /* GIMPLE codes hash value.  */
 372   hashval_t gcode_hash;
 373
 374   /* Vector of subpart of memory access types.  */
 375   auto_vec<tree> memory_access_types;
 376
 377   /* Total number of SSA names used in the function.  */
 378   unsigned ssa_names_size;
 379
 380   /* Array of structures for all basic blocks.  */
 381   vec <ipa_icf_gimple::sem_bb *> bb_sorted;
 382
 383   /* Hash of canonical types used for memory references in the
 384      function.  */
 385   hashval_t m_alias_sets_hash;
 386
 387   /* Return true if parameter I may be used.  */
 388   bool param_used_p (unsigned int i);
 389
 390 private:
 391   /* Calculates hash value based on a BASIC_BLOCK.  */
 392   hashval_t get_bb_hash (const ipa_icf_gimple::sem_bb *basic_block);
 393
 394   /* For given basic blocks BB1 and BB2 (from functions FUNC1 and FUNC),
 395      true value is returned if phi nodes are semantically
 396      equivalent in these blocks .  */
 397   bool compare_phi_node (basic_block bb1, basic_block bb2);
 398
 399   /* Basic blocks dictionary BB_DICT returns true if SOURCE index BB
 400      corresponds to TARGET.  */
 401   bool bb_dict_test (vec<int> *bb_dict, int source, int target);
 402
 403   /* If cgraph edges E1 and E2 are indirect calls, verify that
 404      ICF flags are the same.  */
 405   bool compare_edge_flags (cgraph_edge *e1, cgraph_edge *e2);
 406
 407   /* Processes function equality comparison.  */
 408   bool equals_private (sem_item *item);
 409
 410   /* Function checker stores binding between functions.   */
 411   ipa_icf_gimple::func_checker *m_checker;
 412
 413   /* COMPARED_FUNC is a function that we compare to.  */
 414   sem_function *m_compared_func;
 415 }; // class sem_function
 416
 417 class sem_variable: public sem_item
 418 {
 419 public:
 420   /* Semantic variable constructor that uses STACK as bitmap memory stack.  */
 421   sem_variable (bitmap_obstack *stack);
 422
 423   /*  Constructor based on callgraph node _NODE.
 424       Bitmap STACK is used for memory allocation.  */
 425
 426   sem_variable (varpool_node *_node, bitmap_obstack *stack);
 427
 428   /* Semantic variable initialization function.  */
 429   virtual void init (ipa_icf_gimple::func_checker *);
 430
 431   virtual hashval_t get_hash (void);
 432   virtual bool merge (sem_item *alias_item);
 433   virtual void dump_to_file (FILE *file);
 434   virtual bool equals (sem_item *item,
 435                        hash_map <symtab_node *, sem_item *> &ignored_nodes);
 436
 437   /* Fast equality variable based on knowledge known in WPA.  */
 438   virtual bool equals_wpa (sem_item *item,
 439                            hash_map <symtab_node *, sem_item *> &ignored_nodes);
 440
 441   /* Returns varpool_node.  */
 442   inline varpool_node *get_node (void)
 443   {
 444     return dyn_cast <varpool_node *> (node);
 445   }
 446
 447   /* Parser function that visits a varpool NODE.  */
 448   static sem_variable *parse (varpool_node *node, bitmap_obstack *stack,
 449                               ipa_icf_gimple::func_checker *checker);
 450
 451 private:
 452   /* Compares trees T1 and T2 for semantic equality.  */
 453   static bool equals (tree t1, tree t2);
 454 }; // class sem_variable
 455
 456 class sem_item_optimizer;
 457
 458 struct congruence_class_group
 459 {
 460   hashval_t hash;
 461   sem_item_type type;
 462   vec <congruence_class *> classes;
 463 };
 464
 465 /* Congruence class set structure.  */
 466 struct congruence_class_hash : nofree_ptr_hash <congruence_class_group>
 467 {
 468   static inline hashval_t hash (const congruence_class_group *item)
 469   {
 470     return item->hash;
 471   }
 472
 473   static inline int equal (const congruence_class_group *item1,
 474                            const congruence_class_group *item2)
 475   {
 476     return item1->hash == item2->hash && item1->type == item2->type;
 477   }
 478 };
 479
 480 struct traverse_split_pair
 481 {
 482   sem_item_optimizer *optimizer;
 483   class congruence_class *cls;
 484 };
 485
 486 /* Semantic item optimizer includes all top-level logic
 487    related to semantic equality comparison.  */
 488 class sem_item_optimizer
 489 {
 490 public:
 491   sem_item_optimizer ();
 492   ~sem_item_optimizer ();
 493
 494   /* Function responsible for visiting all potential functions and
 495      read-only variables that can be merged.  */
 496   void parse_funcs_and_vars (void);
 497
 498   /* Optimizer entry point which returns true in case it processes
 499      a merge operation. True is returned if there's a merge operation
 500      processed.  */
 501   bool execute (void);
 502
 503   /* Dump function. */
 504   void dump (void);
 505
 506   /* Verify congruence classes if checking is enabled.  */
 507   void checking_verify_classes (void);
 508
 509   /* Verify congruence classes.  */
 510   void verify_classes (void);
 511
 512   /* Write IPA ICF summary for symbols.  */
 513   void write_summary (void);
 514
 515   /* Read IPA ICF summary for symbols.  */
 516   void read_summary (void);
 517
 518   /* Callgraph removal hook called for a NODE with a custom DATA.  */
 519   static void cgraph_removal_hook (cgraph_node *node, void *data);
 520
 521   /* Varpool removal hook called for a NODE with a custom DATA.  */
 522   static void varpool_removal_hook (varpool_node *node, void *data);
 523
 524   /* Worklist of congruence classes that can potentially
 525      refine classes of congruence.  */
 526   fibonacci_heap<unsigned, congruence_class> worklist;
 527
 528   /* Remove semantic ITEM and release memory.  */
 529   void remove_item (sem_item *item);
 530
 531   /* Remove symtab NODE triggered by symtab removal hooks.  */
 532   void remove_symtab_node (symtab_node *node);
 533
 534   /* Register callgraph and varpool hooks.  */
 535   void register_hooks (void);
 536
 537   /* Unregister callgraph and varpool hooks.  */
 538   void unregister_hooks (void);
 539
 540   /* Adds a CLS to hashtable associated by hash value.  */
 541   void add_class (congruence_class *cls);
 542
 543   /* Gets a congruence class group based on given HASH value and TYPE.  */
 544   congruence_class_group *get_group_by_hash (hashval_t hash,
 545       sem_item_type type);
 546 private:
 547
 548   /* For each semantic item, append hash values of references.  */
 549   void update_hash_by_addr_refs ();
 550
 551   /* Update hash by canonical types of memory accesses.  */
 552   void update_hash_by_memory_access_type ();
 553
 554   /* Congruence classes are built by hash value.  */
 555   void build_hash_based_classes (void);
 556
 557   /* Semantic items in classes having more than one element and initialized.
 558      In case of WPA, we load function body.  */
 559   unsigned int parse_nonsingleton_classes (void);
 560
 561   /* Equality function for semantic items is used to subdivide existing
 562      classes. If IN_WPA, fast equality function is invoked.  */
 563   void subdivide_classes_by_equality (bool in_wpa = false);
 564
 565   /* Subdivide classes by address and interposable references
 566      that members of the class reference.
 567      Example can be a pair of functions that have an address
 568      taken from a function. If these addresses are different the class
 569      is split.  */
 570   unsigned subdivide_classes_by_sensitive_refs();
 571
 572   /* Debug function prints all informations about congruence classes.  */
 573   void dump_cong_classes (void);
 574
 575   /* Build references according to call graph.  */
 576   void build_graph (void);
 577
 578   /* Iterative congruence reduction function.  */
 579   void process_cong_reduction (void);
 580
 581   /* After reduction is done, we can declare all items in a group
 582      to be equal. PREV_CLASS_COUNT is start number of classes
 583      before reduction. True is returned if there's a merge operation
 584      processed.  LOADED_SYMBOLS is number of symbols that were loaded
 585      in WPA.  */
 586   bool merge_classes (unsigned int prev_class_count,
 587                       unsigned int loaded_symbols);
 588
 589   /* Fixup points to analysis info.  */
 590   void fixup_points_to_sets (void);
 591
 592   /* Fixup points to set PT.  */
 593   void fixup_pt_set (struct pt_solution *pt);
 594
 595   /* Adds a newly created congruence class CLS to worklist.  */
 596   void worklist_push (congruence_class *cls);
 597
 598   /* Pops a class from worklist. */
 599   congruence_class *worklist_pop ();
 600
 601   /* Every usage of a congruence class CLS is a candidate that can split the
 602      collection of classes. Bitmap stack BMSTACK is used for bitmap
 603      allocation.  */
 604   void do_congruence_step (congruence_class *cls);
 605
 606   /* Tests if a class CLS used as INDEXth splits any congruence classes.
 607      Bitmap stack BMSTACK is used for bitmap allocation.  */
 608   bool do_congruence_step_for_index (congruence_class *cls, unsigned int index);
 609
 610   /* Makes pairing between a congruence class CLS and semantic ITEM.  */
 611   static void add_item_to_class (congruence_class *cls, sem_item *item);
 612
 613   /* Disposes split map traverse function. CLS is congruence
 614      class, BSLOT is bitmap slot we want to release. DATA is mandatory,
 615      but unused argument.  */
 616   static bool release_split_map (congruence_class * const &cls, bitmap const &b,
 617                                  traverse_split_pair *pair);
 618
 619   /* Process split operation for a congruence class CLS,
 620      where bitmap B splits congruence class members. DATA is used
 621      as argument of split pair.  */
 622   static bool traverse_congruence_split (congruence_class * const &cls,
 623                                          bitmap const &b,
 624                                          traverse_split_pair *pair);
 625
 626   /* Compare function for sorting pairs in do_congruence_step_f.  */
 627   static int sort_congruence_split (const void *, const void *);
 628
 629   /* Reads a section from LTO stream file FILE_DATA. Input block for DATA
 630      contains LEN bytes.  */
 631   void read_section (lto_file_decl_data *file_data, const char *data,
 632                      size_t len);
 633
 634   /* Removes all callgraph and varpool nodes that are marked by symtab
 635      as deleted.  */
 636   void filter_removed_items (void);
 637
 638   /* Vector of semantic items.  */
 639   vec <sem_item *> m_items;
 640
 641   /* A set containing all items removed by hooks.  */
 642   hash_set <symtab_node *> m_removed_items_set;
 643
 644   /* Hashtable of congruence classes.  */
 645   hash_table <congruence_class_hash> m_classes;
 646
 647   /* Count of congruence classes.  */
 648   unsigned int m_classes_count;
 649
 650   /* Map data structure maps symtab nodes to semantic items.  */
 651   hash_map <symtab_node *, sem_item *> m_symtab_node_map;
 652
 653   /* Set to true if a splitter class is removed.  */
 654   bool splitter_class_removed;
 655
 656   /* Global unique class id counter.  */
 657   static unsigned int class_id;
 658
 659   /* Callgraph node removal hook holder.  */
 660   cgraph_node_hook_list *m_cgraph_node_hooks;
 661
 662   /* Varpool node removal hook holder.  */
 663   varpool_node_hook_list *m_varpool_node_hooks;
 664
 665   /* Bitmap stack.  */
 666   bitmap_obstack m_bmstack;
 667
 668   /* Vector of merged variables.  Needed for fixup of points-to-analysis
 669      info.  */
 670   vec <symtab_pair> m_merged_variables;
 671
 672   /* Hash map will all references.  */
 673   ref_map m_references;
 674 }; // class sem_item_optimizer
 675
 676 } // ipa_icf namespace