gcc/stringpool.c

   1 /* String pool for GCC.
   2    Copyright (C) 2000-2018 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 /* String text, identifier text and identifier node allocator.
  21    Identifiers are uniquely stored in a hash table.
  22
  23    We use cpplib's hash table implementation.  libiberty's
  24    hashtab.c is not used because it requires 100% average space
  25    overhead per string, which is unacceptable.  Also, this algorithm
  26    is faster.  */
  27
  28 #include "config.h"
  29 #include "system.h"
  30 #include "coretypes.h"
  31 #include "tree.h"
  32
  33 struct ht *ident_hash;
  34
  35 static hashnode alloc_node (cpp_hash_table *);
  36 static int mark_ident (struct cpp_reader *, hashnode, const void *);
  37
  38 static void *
  39 stringpool_ggc_alloc (size_t x)
  40 {
  41   return ggc_alloc_atomic (x);
  42 }
  43
  44 /* Initialize the string pool.  */
  45 void
  46 init_stringpool (void)
  47 {
  48   /* Clean up if we're called more than once.
  49      (We can't make this idempotent since identifiers contain state) */
  50   if (ident_hash)
  51     ht_destroy (ident_hash);
  52
  53   /* Create with 16K (2^14) entries.  */
  54   ident_hash = ht_create (14);
  55   ident_hash->alloc_node = alloc_node;
  56   ident_hash->alloc_subobject = stringpool_ggc_alloc;
  57 }
  58
  59 /* Allocate a hash node.  */
  60 static hashnode
  61 alloc_node (cpp_hash_table *table ATTRIBUTE_UNUSED)
  62 {
  63   return GCC_IDENT_TO_HT_IDENT (make_node (IDENTIFIER_NODE));
  64 }
  65
  66 /* Allocate and return a string constant of length LENGTH, containing
  67    CONTENTS.  If LENGTH is -1, CONTENTS is assumed to be a
  68    nul-terminated string, and the length is calculated using strlen.  */
  69
  70 const char *
  71 ggc_alloc_string (const char *contents, int length MEM_STAT_DECL)
  72 {
  73   if (length == -1)
  74     length = strlen (contents);
  75
  76   if (!length)
  77     return "";
  78
  79   char *result = (char *) ggc_alloc_atomic (length + 1);
  80   memcpy (result, contents, length);
  81   result[length] = '\0';
  82
  83   return (const char *) result;
  84 }
  85
  86 /* Return an IDENTIFIER_NODE whose name is TEXT (a null-terminated string).
  87    If an identifier with that name has previously been referred to,
  88    the same node is returned this time.  */
  89
  90 #undef get_identifier
  91
  92 tree
  93 get_identifier (const char *text)
  94 {
  95   hashnode ht_node = ht_lookup (ident_hash,
  96                                 (const unsigned char *) text,
  97                                 strlen (text), HT_ALLOC);
  98
  99   /* ht_node can't be NULL here.  */
 100   return HT_IDENT_TO_GCC_IDENT (ht_node);
 101 }
 102
 103 /* Identical to get_identifier, except that the length is assumed
 104    known.  */
 105
 106 tree
 107 get_identifier_with_length (const char *text, size_t length)
 108 {
 109   hashnode ht_node = ht_lookup (ident_hash,
 110                                 (const unsigned char *) text,
 111                                 length, HT_ALLOC);
 112
 113   /* ht_node can't be NULL here.  */
 114   return HT_IDENT_TO_GCC_IDENT (ht_node);
 115 }
 116
 117 /* If an identifier with the name TEXT (a null-terminated string) has
 118    previously been referred to, return that node; otherwise return
 119    NULL_TREE.  */
 120
 121 tree
 122 maybe_get_identifier (const char *text)
 123 {
 124   hashnode ht_node;
 125
 126   ht_node = ht_lookup (ident_hash, (const unsigned char *) text,
 127                        strlen (text), HT_NO_INSERT);
 128   if (ht_node)
 129     return HT_IDENT_TO_GCC_IDENT (ht_node);
 130
 131   return NULL_TREE;
 132 }
 133
 134 /* Report some basic statistics about the string pool.  */
 135
 136 void
 137 stringpool_statistics (void)
 138 {
 139   ht_dump_statistics (ident_hash);
 140 }
 141 \f
 142 /* Mark an identifier for GC.  */
 143
 144 static int
 145 mark_ident (struct cpp_reader *pfile ATTRIBUTE_UNUSED, hashnode h,
 146             const void *v ATTRIBUTE_UNUSED)
 147 {
 148   gt_ggc_m_9tree_node (HT_IDENT_TO_GCC_IDENT (h));
 149   return 1;
 150 }
 151
 152 /* Return true if an identifier should be removed from the table.  */
 153
 154 static int
 155 maybe_delete_ident (struct cpp_reader *pfile ATTRIBUTE_UNUSED, hashnode h,
 156                     const void *v ATTRIBUTE_UNUSED)
 157 {
 158   return !ggc_marked_p (HT_IDENT_TO_GCC_IDENT (h));
 159 }
 160
 161 /* Mark the trees hanging off the identifier node for GGC.  These are
 162    handled specially (not using gengtype) because identifiers are only
 163    roots during one part of compilation.  */
 164
 165 void
 166 ggc_mark_stringpool (void)
 167 {
 168   ht_forall (ident_hash, mark_ident, NULL);
 169 }
 170
 171 /* Purge the identifier hash of identifiers which are no longer
 172    referenced.  */
 173
 174 void
 175 ggc_purge_stringpool (void)
 176 {
 177   ht_purge (ident_hash, maybe_delete_ident, NULL);
 178 }
 179
 180 /* Pointer-walking routine for strings (not very interesting, since
 181    strings don't contain pointers).  */
 182
 183 void
 184 gt_pch_p_S (void *obj ATTRIBUTE_UNUSED, void *x ATTRIBUTE_UNUSED,
 185             gt_pointer_operator op ATTRIBUTE_UNUSED,
 186             void *cookie ATTRIBUTE_UNUSED)
 187 {
 188 }
 189
 190 /* PCH pointer-walking routine for strings.  */
 191
 192 void
 193 gt_pch_n_S (const void *x)
 194 {
 195   gt_pch_note_object (CONST_CAST (void *, x), CONST_CAST (void *, x),
 196                       &gt_pch_p_S);
 197 }
 198
 199
 200 /* User-callable entry point for marking string X.  */
 201
 202 void
 203 gt_pch_nx (const char *& x)
 204 {
 205   gt_pch_n_S (x);
 206 }
 207
 208 void
 209 gt_pch_nx (unsigned char *& x)
 210 {
 211   gt_pch_n_S (x);
 212 }
 213
 214 void
 215 gt_pch_nx (unsigned char& x ATTRIBUTE_UNUSED)
 216 {
 217 }
 218
 219 void
 220 gt_pch_nx (unsigned char *x, gt_pointer_operator op, void *cookie)
 221 {
 222   op (x, cookie);
 223 }
 224 \f
 225 /* Handle saving and restoring the string pool for PCH.  */
 226
 227 /* SPD is saved in the PCH file and holds the information needed
 228    to restore the string pool.  */
 229
 230 struct GTY(()) string_pool_data {
 231   ht_identifier_ptr *
 232     GTY((length ("%h.nslots"),
 233          nested_ptr (union tree_node, "%h ? GCC_IDENT_TO_HT_IDENT (%h) : NULL",
 234                      "%h ? HT_IDENT_TO_GCC_IDENT (%h) : NULL")))
 235     entries;
 236   unsigned int nslots;
 237   unsigned int nelements;
 238 };
 239
 240 static GTY(()) struct string_pool_data * spd;
 241
 242 /* Save the stringpool data in SPD.  */
 243
 244 void
 245 gt_pch_save_stringpool (void)
 246 {
 247   spd = ggc_alloc<string_pool_data> ();
 248   spd->nslots = ident_hash->nslots;
 249   spd->nelements = ident_hash->nelements;
 250   spd->entries = ggc_vec_alloc<ht_identifier_ptr> (spd->nslots);
 251   memcpy (spd->entries, ident_hash->entries,
 252           spd->nslots * sizeof (spd->entries[0]));
 253 }
 254
 255 /* Return the stringpool to its state before gt_pch_save_stringpool
 256    was called.  */
 257
 258 void
 259 gt_pch_fixup_stringpool (void)
 260 {
 261 }
 262
 263 /* A PCH file has been restored, which loaded SPD; fill the real hash table
 264    from SPD.  */
 265
 266 void
 267 gt_pch_restore_stringpool (void)
 268 {
 269   ht_load (ident_hash, spd->entries, spd->nslots, spd->nelements, false);
 270   spd = NULL;
 271 }
 272
 273 #include "gt-stringpool.h"