libcpp/symtab.cc

   1 /* Hash tables.
   2    Copyright (C) 2000-2023 Free Software Foundation, Inc.
   3
   4 This program is free software; you can redistribute it and/or modify it
   5 under the terms of the GNU General Public License as published by the
   6 Free Software Foundation; either version 3, or (at your option) any
   7 later version.
   8
   9 This program is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program; see the file COPYING3.  If not see
  16 <http://www.gnu.org/licenses/>.
  17
  18  In other words, you are welcome to use, share and improve this program.
  19  You are forbidden to forbid anyone else to use, share and improve
  20  what you give them.   Help stamp out software-hoarding!  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "symtab.h"
  25
  26 /* The code below is a specialization of Vladimir Makarov's expandable
  27    hash tables (see libiberty/hashtab.c).  The abstraction penalty was
  28    too high to continue using the generic form.  This code knows
  29    intrinsically how to calculate a hash value, and how to compare an
  30    existing entry with a potential new one.  */
  31
  32 static unsigned int calc_hash (const unsigned char *, size_t);
  33 static void ht_expand (cpp_hash_table *);
  34 static double approx_sqrt (double);
  35
  36 /* A deleted entry.  */
  37 #define DELETED ((hashnode) -1)
  38
  39 /* Calculate the hash of the string STR of length LEN.  */
  40
  41 static unsigned int
  42 calc_hash (const unsigned char *str, size_t len)
  43 {
  44   size_t n = len;
  45   unsigned int r = 0;
  46
  47   while (n--)
  48     r = HT_HASHSTEP (r, *str++);
  49
  50   return HT_HASHFINISH (r, len);
  51 }
  52
  53 /* Initialize an identifier hashtable.  */
  54
  55 cpp_hash_table *
  56 ht_create (unsigned int order)
  57 {
  58   unsigned int nslots = 1 << order;
  59   cpp_hash_table *table;
  60
  61   table = XCNEW (cpp_hash_table);
  62
  63   /* Strings need no alignment.  */
  64   obstack_specify_allocation (&table->stack, 0, 0, xmalloc, free);
  65
  66   obstack_alignment_mask (&table->stack) = 0;
  67
  68   table->entries = XCNEWVEC (hashnode, nslots);
  69   table->entries_owned = true;
  70   table->nslots = nslots;
  71   return table;
  72 }
  73
  74 /* Frees all memory associated with a hash table.  */
  75
  76 void
  77 ht_destroy (cpp_hash_table *table)
  78 {
  79   obstack_free (&table->stack, NULL);
  80   if (table->entries_owned)
  81     free (table->entries);
  82   free (table);
  83 }
  84
  85 /* Returns the hash entry for the a STR of length LEN.  If that string
  86    already exists in the table, returns the existing entry.  If the
  87    identifier hasn't been seen before, and INSERT is CPP_NO_INSERT,
  88    returns NULL.  Otherwise insert and returns a new entry.  A new
  89    string is allocated.  */
  90 hashnode
  91 ht_lookup (cpp_hash_table *table, const unsigned char *str, size_t len,
  92            enum ht_lookup_option insert)
  93 {
  94   return ht_lookup_with_hash (table, str, len, calc_hash (str, len),
  95                               insert);
  96 }
  97
  98 hashnode
  99 ht_lookup_with_hash (cpp_hash_table *table, const unsigned char *str,
 100                      size_t len, unsigned int hash,
 101                      enum ht_lookup_option insert)
 102 {
 103   unsigned int hash2;
 104   unsigned int index;
 105   unsigned int deleted_index = table->nslots;
 106   size_t sizemask;
 107   hashnode node;
 108
 109   sizemask = table->nslots - 1;
 110   index = hash & sizemask;
 111   table->searches++;
 112
 113   node = table->entries[index];
 114
 115   if (node != NULL)
 116     {
 117       if (node == DELETED)
 118         deleted_index = index;
 119       else if (node->hash_value == hash
 120                && HT_LEN (node) == (unsigned int) len
 121                && !memcmp (HT_STR (node), str, len))
 122         return node;
 123
 124       /* hash2 must be odd, so we're guaranteed to visit every possible
 125          location in the table during rehashing.  */
 126       hash2 = ((hash * 17) & sizemask) | 1;
 127
 128       for (;;)
 129         {
 130           table->collisions++;
 131           index = (index + hash2) & sizemask;
 132           node = table->entries[index];
 133           if (node == NULL)
 134             break;
 135
 136           if (node == DELETED)
 137             {
 138               if (deleted_index != table->nslots)
 139                 deleted_index = index;
 140             }
 141           else if (node->hash_value == hash
 142                    && HT_LEN (node) == (unsigned int) len
 143                    && !memcmp (HT_STR (node), str, len))
 144             return node;
 145         }
 146     }
 147
 148   if (insert == HT_NO_INSERT)
 149     return NULL;
 150
 151   /* We prefer to overwrite the first deleted slot we saw.  */
 152   if (deleted_index != table->nslots)
 153     index = deleted_index;
 154
 155   node = (*table->alloc_node) (table);
 156   table->entries[index] = node;
 157
 158   HT_LEN (node) = (unsigned int) len;
 159   node->hash_value = hash;
 160
 161   if (table->alloc_subobject)
 162     {
 163       char *chars = (char *) table->alloc_subobject (len + 1);
 164       memcpy (chars, str, len);
 165       chars[len] = '\0';
 166       HT_STR (node) = (const unsigned char *) chars;
 167     }
 168   else
 169     HT_STR (node) = (const unsigned char *) obstack_copy0 (&table->stack,
 170                                                            str, len);
 171
 172   if (++table->nelements * 4 >= table->nslots * 3)
 173     /* Must expand the string table.  */
 174     ht_expand (table);
 175
 176   return node;
 177 }
 178
 179 /* Double the size of a hash table, re-hashing existing entries.  */
 180
 181 static void
 182 ht_expand (cpp_hash_table *table)
 183 {
 184   hashnode *nentries, *p, *limit;
 185   unsigned int size, sizemask;
 186
 187   size = table->nslots * 2;
 188   nentries = XCNEWVEC (hashnode, size);
 189   sizemask = size - 1;
 190
 191   p = table->entries;
 192   limit = p + table->nslots;
 193   do
 194     if (*p && *p != DELETED)
 195       {
 196         unsigned int index, hash, hash2;
 197
 198         hash = (*p)->hash_value;
 199         index = hash & sizemask;
 200
 201         if (nentries[index])
 202           {
 203             hash2 = ((hash * 17) & sizemask) | 1;
 204             do
 205               {
 206                 index = (index + hash2) & sizemask;
 207               }
 208             while (nentries[index]);
 209           }
 210         nentries[index] = *p;
 211       }
 212   while (++p < limit);
 213
 214   if (table->entries_owned)
 215     free (table->entries);
 216   table->entries_owned = true;
 217   table->entries = nentries;
 218   table->nslots = size;
 219 }
 220
 221 /* For all nodes in TABLE, callback CB with parameters TABLE->PFILE,
 222    the node, and V.  */
 223 void
 224 ht_forall (cpp_hash_table *table, ht_cb cb, const void *v)
 225 {
 226   hashnode *p, *limit;
 227
 228   p = table->entries;
 229   limit = p + table->nslots;
 230   do
 231     if (*p && *p != DELETED)
 232       {
 233         if ((*cb) (table->pfile, *p, v) == 0)
 234           break;
 235       }
 236   while (++p < limit);
 237 }
 238
 239 /* Like ht_forall, but a nonzero return from the callback means that
 240    the entry should be removed from the table.  */
 241 void
 242 ht_purge (cpp_hash_table *table, ht_cb cb, const void *v)
 243 {
 244   hashnode *p, *limit;
 245
 246   p = table->entries;
 247   limit = p + table->nslots;
 248   do
 249     if (*p && *p != DELETED)
 250       {
 251         if ((*cb) (table->pfile, *p, v))
 252           *p = DELETED;
 253       }
 254   while (++p < limit);
 255 }
 256
 257 /* Restore the hash table.  */
 258 void
 259 ht_load (cpp_hash_table *ht, hashnode *entries,
 260          unsigned int nslots, unsigned int nelements,
 261          bool own)
 262 {
 263   if (ht->entries_owned)
 264     free (ht->entries);
 265   ht->entries = entries;
 266   ht->nslots = nslots;
 267   ht->nelements = nelements;
 268   ht->entries_owned = own;
 269 }
 270
 271 /* Dump allocation statistics to stderr.  */
 272
 273 void
 274 ht_dump_statistics (cpp_hash_table *table)
 275 {
 276   size_t nelts, nids, overhead, headers;
 277   size_t total_bytes, longest, deleted = 0;
 278   double sum_of_squares, exp_len, exp_len2, exp2_len;
 279   hashnode *p, *limit;
 280
 281 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
 282                   ? (x) \
 283                   : ((x) < 1024*1024*10 \
 284                      ? (x) / 1024 \
 285                      : (x) / (1024*1024))))
 286 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
 287
 288   total_bytes = longest = sum_of_squares = nids = 0;
 289   p = table->entries;
 290   limit = p + table->nslots;
 291   do
 292     if (*p == DELETED)
 293       ++deleted;
 294     else if (*p)
 295       {
 296         size_t n = HT_LEN (*p);
 297
 298         total_bytes += n;
 299         sum_of_squares += (double) n * n;
 300         if (n > longest)
 301           longest = n;
 302         nids++;
 303       }
 304   while (++p < limit);
 305
 306   nelts = table->nelements;
 307   headers = table->nslots * sizeof (hashnode);
 308
 309   fprintf (stderr, "\nString pool\n%-32s%lu\n", "entries:",
 310            (unsigned long) nelts);
 311   fprintf (stderr, "%-32s%lu (%.2f%%)\n", "identifiers:",
 312            (unsigned long) nids, nids * 100.0 / nelts);
 313   fprintf (stderr, "%-32s%lu\n", "slots:",
 314            (unsigned long) table->nslots);
 315   fprintf (stderr, "%-32s%lu\n", "deleted:",
 316            (unsigned long) deleted);
 317
 318   if (table->alloc_subobject)
 319     fprintf (stderr, "%-32s%lu%c\n", "GGC bytes:",
 320              SCALE (total_bytes), LABEL (total_bytes));
 321   else
 322     {
 323       overhead = obstack_memory_used (&table->stack) - total_bytes;
 324       fprintf (stderr, "%-32s%lu%c (%lu%c overhead)\n",
 325                "obstack bytes:",
 326                SCALE (total_bytes), LABEL (total_bytes),
 327                SCALE (overhead), LABEL (overhead));
 328     }
 329   fprintf (stderr, "%-32s%lu%c\n", "table size:",
 330            SCALE (headers), LABEL (headers));
 331
 332   exp_len = (double)total_bytes / (double)nelts;
 333   exp2_len = exp_len * exp_len;
 334   exp_len2 = (double) sum_of_squares / (double) nelts;
 335
 336   fprintf (stderr, "%-32s%.4f\n", "coll/search:",
 337            (double) table->collisions / (double) table->searches);
 338   fprintf (stderr, "%-32s%.4f\n", "ins/search:",
 339            (double) nelts / (double) table->searches);
 340   fprintf (stderr, "%-32s%.2f bytes (+/- %.2f)\n",
 341            "avg. entry:",
 342            exp_len, approx_sqrt (exp_len2 - exp2_len));
 343   fprintf (stderr, "%-32s%lu\n", "longest entry:",
 344            (unsigned long) longest);
 345 #undef SCALE
 346 #undef LABEL
 347 }
 348
 349 /* Return the approximate positive square root of a number N.  This is for
 350    statistical reports, not code generation.  */
 351 static double
 352 approx_sqrt (double x)
 353 {
 354   double s, d;
 355
 356   if (x < 0)
 357     abort ();
 358   if (x == 0)
 359     return 0;
 360
 361   s = x;
 362   do
 363     {
 364       d = (s * s - x) / (2 * s);
 365       s -= d;
 366     }
 367   while (d > .0001);
 368   return s;
 369 }