src/symtab.c

   1 /* GNU m4 -- A simple macro processor
   2
   3    Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 2003, 2006, 2007, 2008
   4    Free Software Foundation, Inc.
   5
   6    This file is part of GNU M4.
   7
   8    GNU M4 is free software: you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation, either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    GNU M4 is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 /* This file handles all the low level work around the symbol table.  The
  23    symbol table is a simple chained hash table.  Each symbol is described
  24    by a struct symbol, which is placed in the hash table based upon the
  25    symbol name.  Symbols that hash to the same entry in the table are
  26    kept on a list, sorted by name.  As a special case, to facilitate the
  27    "pushdef" and "popdef" builtins, a symbol can be several times in the
  28    symbol table, one for each definition.  Since the name is the same,
  29    all the entries for the symbol will be on the same list, and will
  30    also, because the list is sorted, be adjacent.  All the entries for a
  31    name are simply ordered on the list by age.  The current definition
  32    will then always be the first found.  */
  33
  34 #include "m4.h"
  35
  36 #ifdef DEBUG_SYM
  37 /* When evaluating hash table performance, this profiling code shows
  38    how many collisions were encountered.  */
  39
  40 struct profile
  41 {
  42   int entry; /* Number of times lookup_symbol called with this mode.  */
  43   int comparisons; /* Number of times strcmp was called.  */
  44   int misses; /* Number of times strcmp did not return 0.  */
  45   long long bytes; /* Number of bytes compared.  */
  46 };
  47
  48 static struct profile profiles[5];
  49 static symbol_lookup current_mode;
  50
  51 /* On exit, show a profile of symbol table performance.  */
  52 static void
  53 show_profile (void)
  54 {
  55   int i;
  56   for (i = 0; i < 5; i++)
  57     {
  58       xfprintf(stderr, "m4: lookup mode %d called %d times, %d compares, "
  59                "%d misses, %lld bytes\n",
  60                i, profiles[i].entry, profiles[i].comparisons,
  61                profiles[i].misses, profiles[i].bytes);
  62     }
  63 }
  64
  65 /* Like strcmp (S1, S2), but also track profiling statistics.  */
  66 static int
  67 profile_strcmp (const char *s1, const char *s2)
  68 {
  69   int i = 1;
  70   int result;
  71   while (*s1 && *s1 == *s2)
  72     {
  73       s1++;
  74       s2++;
  75       i++;
  76     }
  77   result = (unsigned char) *s1 - (unsigned char) *s2;
  78   profiles[current_mode].comparisons++;
  79   if (result != 0)
  80     profiles[current_mode].misses++;
  81   profiles[current_mode].bytes += i;
  82   return result;
  83 }
  84
  85 # define strcmp profile_strcmp
  86 #endif /* DEBUG_SYM */
  87
  88 \f
  89 /*----------------------------------------------------------------------.
  90 | Initialise the symbol table, by allocating the necessary storage, and |
  91 | zeroing all the entries.                                              |
  92 `----------------------------------------------------------------------*/
  93
  94 /* Pointer to symbol table.  */
  95 symbol **symtab;
  96
  97 void
  98 symtab_init (void)
  99 {
 100   size_t i;
 101   symbol **s;
 102
 103   s = symtab = (symbol **) xnmalloc (hash_table_size, sizeof (symbol *));
 104
 105   for (i = 0; i < hash_table_size; i++)
 106     s[i] = NULL;
 107
 108 #ifdef DEBUG_SYM
 109   atexit (show_profile); /* Ignore failure, since this is debug code.  */
 110 #endif /* DEBUG_SYM */
 111 }
 112
 113 /*--------------------------------------------------.
 114 | Return a hashvalue for a string, from GNU-emacs.  |
 115 `--------------------------------------------------*/
 116
 117 static size_t
 118 hash (const char *s)
 119 {
 120   register size_t val = 0;
 121
 122   register const char *ptr = s;
 123   register char ch;
 124
 125   while ((ch = *ptr++) != '\0')
 126     val = (val << 7) + (val >> (sizeof (val) * CHAR_BIT - 7)) + ch;
 127   return val;
 128 }
 129
 130 /*--------------------------------------------.
 131 | Free all storage associated with a symbol.  |
 132 `--------------------------------------------*/
 133
 134 void
 135 free_symbol (symbol *sym)
 136 {
 137   if (SYMBOL_PENDING_EXPANSIONS (sym) > 0)
 138     SYMBOL_DELETED (sym) = true;
 139   else
 140     {
 141       free (SYMBOL_NAME (sym));
 142       if (SYMBOL_TYPE (sym) == TOKEN_TEXT)
 143         free (SYMBOL_TEXT (sym));
 144       free (sym);
 145     }
 146 }
 147
 148 /*-------------------------------------------------------------------.
 149 | Search in, and manipulation of the symbol table, are all done by   |
 150 | lookup_symbol ().  It basically hashes NAME to a list in the       |
 151 | symbol table, and searches this list for the first occurrence of a |
 152 | symbol with the name.                                              |
 153 |                                                                    |
 154 | The MODE parameter determines what lookup_symbol () will do.  It   |
 155 | can either just do a lookup, do a lookup and insert if not         |
 156 | present, do an insertion even if the name is already in the list,  |
 157 | delete the first occurrence of the name on the list, or delete all |
 158 | occurrences of the name on the list.                               |
 159 `-------------------------------------------------------------------*/
 160
 161 symbol *
 162 lookup_symbol (const char *name, symbol_lookup mode)
 163 {
 164   size_t h;
 165   int cmp = 1;
 166   symbol *sym, *prev;
 167   symbol **spp;
 168
 169 #if DEBUG_SYM
 170   current_mode = mode;
 171   profiles[mode].entry++;
 172 #endif /* DEBUG_SYM */
 173
 174   h = hash (name);
 175   sym = symtab[h % hash_table_size];
 176
 177   for (prev = NULL; sym != NULL; prev = sym, sym = sym->next)
 178     {
 179       cmp = strcmp (SYMBOL_NAME (sym), name);
 180       if (cmp >= 0)
 181         break;
 182     }
 183
 184   /* If just searching, return status of search.  */
 185
 186   if (mode == SYMBOL_LOOKUP)
 187     return cmp == 0 ? sym : NULL;
 188
 189   /* Symbol not found.  */
 190
 191   spp = (prev != NULL) ?  &prev->next : &symtab[h % hash_table_size];
 192
 193   switch (mode)
 194     {
 195
 196     case SYMBOL_INSERT:
 197
 198       /* If the name was found in the table, check whether it is still in
 199          use by a pending expansion.  If so, replace the table element with
 200          a new one; if not, just return the symbol.  If not found, just
 201          insert the name, and return the new symbol.  */
 202
 203       if (cmp == 0 && sym != NULL)
 204         {
 205           if (SYMBOL_PENDING_EXPANSIONS (sym) > 0)
 206             {
 207               symbol *old = sym;
 208               SYMBOL_DELETED (old) = true;
 209
 210               sym = (symbol *) xmalloc (sizeof (symbol));
 211               SYMBOL_TYPE (sym) = TOKEN_VOID;
 212               SYMBOL_TRACED (sym) = SYMBOL_TRACED (old);
 213               SYMBOL_NAME (sym) = xstrdup (name);
 214               SYMBOL_SHADOWED (sym) = false;
 215               SYMBOL_MACRO_ARGS (sym) = false;
 216               SYMBOL_BLIND_NO_ARGS (sym) = false;
 217               SYMBOL_DELETED (sym) = false;
 218               SYMBOL_PENDING_EXPANSIONS (sym) = 0;
 219
 220               SYMBOL_NEXT (sym) = SYMBOL_NEXT (old);
 221               SYMBOL_NEXT (old) = NULL;
 222               (*spp) = sym;
 223             }
 224           return sym;
 225         }
 226       /* Fall through.  */
 227
 228     case SYMBOL_PUSHDEF:
 229
 230       /* Insert a name in the symbol table.  If there is already a symbol
 231          with the name, insert this in front of it, and mark the old
 232          symbol as "shadowed".  */
 233
 234       sym = (symbol *) xmalloc (sizeof (symbol));
 235       SYMBOL_TYPE (sym) = TOKEN_VOID;
 236       SYMBOL_TRACED (sym) = false;
 237       SYMBOL_NAME (sym) = xstrdup (name);
 238       SYMBOL_SHADOWED (sym) = false;
 239       SYMBOL_MACRO_ARGS (sym) = false;
 240       SYMBOL_BLIND_NO_ARGS (sym) = false;
 241       SYMBOL_DELETED (sym) = false;
 242       SYMBOL_PENDING_EXPANSIONS (sym) = 0;
 243
 244       SYMBOL_NEXT (sym) = *spp;
 245       (*spp) = sym;
 246
 247       if (mode == SYMBOL_PUSHDEF && cmp == 0)
 248         {
 249           SYMBOL_SHADOWED (SYMBOL_NEXT (sym)) = true;
 250           SYMBOL_TRACED (sym) = SYMBOL_TRACED (SYMBOL_NEXT (sym));
 251         }
 252       return sym;
 253
 254     case SYMBOL_DELETE:
 255     case SYMBOL_POPDEF:
 256
 257       /* Delete occurrences of symbols with NAME.  SYMBOL_DELETE kills
 258          all definitions, SYMBOL_POPDEF kills only the first.
 259          However, if the last instance of a symbol is marked for
 260          tracing, reinsert a placeholder in the table.  And if the
 261          definition is still in use, let the caller free the memory
 262          after it is done with the symbol.  */
 263
 264       if (cmp != 0 || sym == NULL)
 265         return NULL;
 266       {
 267         bool traced = false;
 268         if (SYMBOL_NEXT (sym) != NULL
 269             && SYMBOL_SHADOWED (SYMBOL_NEXT (sym))
 270             && mode == SYMBOL_POPDEF)
 271           {
 272             SYMBOL_SHADOWED (SYMBOL_NEXT (sym)) = false;
 273             SYMBOL_TRACED (SYMBOL_NEXT (sym)) = SYMBOL_TRACED (sym);
 274           }
 275         else
 276           traced = SYMBOL_TRACED (sym);
 277         do
 278           {
 279             *spp = SYMBOL_NEXT (sym);
 280             free_symbol (sym);
 281             sym = *spp;
 282           }
 283         while (*spp != NULL && SYMBOL_SHADOWED (*spp)
 284                && mode == SYMBOL_DELETE);
 285         if (traced)
 286           {
 287             sym = (symbol *) xmalloc (sizeof (symbol));
 288             SYMBOL_TYPE (sym) = TOKEN_VOID;
 289             SYMBOL_TRACED (sym) = true;
 290             SYMBOL_NAME (sym) = xstrdup (name);
 291             SYMBOL_SHADOWED (sym) = false;
 292             SYMBOL_MACRO_ARGS (sym) = false;
 293             SYMBOL_BLIND_NO_ARGS (sym) = false;
 294             SYMBOL_DELETED (sym) = false;
 295             SYMBOL_PENDING_EXPANSIONS (sym) = 0;
 296
 297             SYMBOL_NEXT (sym) = *spp;
 298             (*spp) = sym;
 299           }
 300       }
 301       return NULL;
 302
 303     default:
 304       assert (!"symbol_lookup");
 305       abort ();
 306     }
 307 }
 308
 309 /*-----------------------------------------------------------------.
 310 | The following function is used for the cases where we want to do |
 311 | something to each and every symbol in the table.  The function   |
 312 | hack_all_symbols () traverses the symbol table, and calls a      |
 313 | specified function FUNC for each symbol in the table.  FUNC is   |
 314 | called with a pointer to the symbol, and the DATA argument.      |
 315 |                                                                  |
 316 | FUNC may safely call lookup_symbol with mode SYMBOL_POPDEF or    |
 317 | SYMBOL_LOOKUP, but any other mode can break the iteration.       |
 318 `-----------------------------------------------------------------*/
 319
 320 void
 321 hack_all_symbols (hack_symbol *func, void *data)
 322 {
 323   size_t h;
 324   symbol *sym;
 325   symbol *next;
 326
 327   for (h = 0; h < hash_table_size; h++)
 328     {
 329       /* We allow func to call SYMBOL_POPDEF, which can invalidate
 330          sym, so we must grab the next element to traverse before
 331          calling func.  */
 332       for (sym = symtab[h]; sym != NULL; sym = next)
 333         {
 334           next = SYMBOL_NEXT (sym);
 335           func (sym, data);
 336         }
 337     }
 338 }
 339 \f
 340 #ifdef DEBUG_SYM
 341
 342 static void symtab_print_list (int i);
 343
 344 static void M4_GNUC_UNUSED
 345 symtab_debug (void)
 346 {
 347   token_data td;
 348   const char *text;
 349   symbol *s;
 350   int delete;
 351   static int i;
 352
 353   while (next_token (&td, NULL, NULL, "<debug>") == TOKEN_WORD)
 354     {
 355       text = TOKEN_DATA_TEXT (&td);
 356       if (*text == '_')
 357         {
 358           delete = 1;
 359           text++;
 360         }
 361       else
 362         delete = 0;
 363
 364       s = lookup_symbol (text, SYMBOL_LOOKUP);
 365
 366       if (s == NULL)
 367         xprintf ("Name `%s' is unknown\n", text);
 368
 369       if (delete)
 370         (void) lookup_symbol (text, SYMBOL_DELETE);
 371       else
 372         (void) lookup_symbol (text, SYMBOL_INSERT);
 373     }
 374   symtab_print_list (i++);
 375 }
 376
 377 static void
 378 symtab_print_list (int i)
 379 {
 380   symbol *sym;
 381   size_t h;
 382
 383   xprintf ("Symbol dump #%d:\n", i);
 384   for (h = 0; h < hash_table_size; h++)
 385     for (sym = symtab[h]; sym != NULL; sym = sym->next)
 386       xprintf ("\tname %s, bucket %lu, addr %p, next %p, "
 387                "flags%s%s%s, pending %d\n",
 388                SYMBOL_NAME (sym),
 389                (unsigned long int) h, sym, SYMBOL_NEXT (sym),
 390                SYMBOL_TRACED (sym) ? " traced" : "",
 391                SYMBOL_SHADOWED (sym) ? " shadowed" : "",
 392                SYMBOL_DELETED (sym) ? " deleted" : "",
 393                SYMBOL_PENDING_EXPANSIONS (sym));
 394 }
 395
 396 #endif /* DEBUG_SYM */