gcc/hash-table.c

/* A type-safe hash table template.
   Copyright (C) 2012-2021 Free Software Foundation, Inc.
   Contributed by Lawrence Crowl <crowl@google.com>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */


/* This file implements a typed hash table.
   The implementation borrows from libiberty's hashtab.  */

#ifdef GENERATOR_FILE
#include "bconfig.h"
#else
#include "config.h"
#endif
#include "system.h"
#include "coretypes.h"
#include "hash-table.h"

/* Table of primes and multiplicative inverses.

   Note that these are not minimally reduced inverses.  Unlike when generating
   code to divide by a constant, we want to be able to use the same algorithm
   all the time.  All of these inverses (are implied to) have bit 32 set.

   For the record, here's the function that computed the table; it's a 
   vastly simplified version of the function of the same name from gcc.  */

struct prime_ent const prime_tab[] = {
  {          7, 0x24924925, 0x9999999b, 2 },
  {         13, 0x3b13b13c, 0x745d1747, 3 },
  {         31, 0x08421085, 0x1a7b9612, 4 },
  {         61, 0x0c9714fc, 0x15b1e5f8, 5 },
  {        127, 0x02040811, 0x0624dd30, 6 },
  {        251, 0x05197f7e, 0x073260a5, 7 },
  {        509, 0x01824366, 0x02864fc8, 8 },
  {       1021, 0x00c0906d, 0x014191f7, 9 },
  {       2039, 0x0121456f, 0x0161e69e, 10 },
  {       4093, 0x00300902, 0x00501908, 11 },
  {       8191, 0x00080041, 0x00180241, 12 },
  {      16381, 0x000c0091, 0x00140191, 13 },
  {      32749, 0x002605a5, 0x002a06e6, 14 },
  {      65521, 0x000f00e2, 0x00110122, 15 },
  {     131071, 0x00008001, 0x00018003, 16 },
  {     262139, 0x00014002, 0x0001c004, 17 },
  {     524287, 0x00002001, 0x00006001, 18 },
  {    1048573, 0x00003001, 0x00005001, 19 },
  {    2097143, 0x00004801, 0x00005801, 20 },
  {    4194301, 0x00000c01, 0x00001401, 21 },
  {    8388593, 0x00001e01, 0x00002201, 22 },
  {   16777213, 0x00000301, 0x00000501, 23 },
  {   33554393, 0x00001381, 0x00001481, 24 },
  {   67108859, 0x00000141, 0x000001c1, 25 },
  {  134217689, 0x000004e1, 0x00000521, 26 },
  {  268435399, 0x00000391, 0x000003b1, 27 },
  {  536870909, 0x00000019, 0x00000029, 28 },
  { 1073741789, 0x0000008d, 0x00000095, 29 },
  { 2147483647, 0x00000003, 0x00000007, 30 },
  /* Avoid "decimal constant so large it is unsigned" for 4294967291.  */
  { 0xfffffffb, 0x00000006, 0x00000008, 31 }
};

/* Limit number of comparisons when calling hash_table<>::verify.  */
unsigned int hash_table_sanitize_eq_limit;

/* The following function returns an index into the above table of the
   nearest prime number which is at least N, and near a power of two. */

unsigned int
hash_table_higher_prime_index (unsigned long n)
{
  unsigned int low = 0;
  unsigned int high = sizeof (prime_tab) / sizeof (prime_tab[0]);

  while (low != high)
    {
      unsigned int mid = low + (high - low) / 2;
      if (n > prime_tab[mid].prime)
	low = mid + 1;
      else
	high = mid;
    }

  /* If we've run out of primes, abort.  */
  gcc_assert (n <= prime_tab[low].prime);

  return low;
}

/* Return a reference to the lazily initialized hash-table usage description.
   This needs to be a function rather than a simple global variable so that it
   is reliably initialized before hash table variables in other files such as
   sem_item::m_type_hash_cache.  */
mem_alloc_description<mem_usage>&
hash_table_usage ()
{
  static mem_alloc_description<mem_usage> usage;
  return usage;
}

/* Support function for statistics.  */
void dump_hash_table_loc_statistics (void)
{
  if (!GATHER_STATISTICS)
    return;

  for (unsigned i = HASH_TABLE_ORIGIN; i <= HASH_SET_ORIGIN; i++)
    {
      mem_alloc_origin origin = (mem_alloc_origin) i;
      hash_table_usage ().dump (origin);
    }
}

/* Report a hash table checking error.  */

ATTRIBUTE_NORETURN ATTRIBUTE_COLD
void
hashtab_chk_error ()
{
  fprintf (stderr, "hash table checking failed: "
	   "equal operator returns true for a pair "
	   "of values with a different hash value\n");
  gcc_unreachable ();
}