/* Implement a cached obstack.
- Written by Fred Fish (fnf@cygnus.com)
- Copyright 1995, 1998 Free Software Foundation, Inc.
+ Written by Fred Fish <fnf@cygnus.com>
+ Rewritten by Jim Blandy <jimb@cygnus.com>
+
+ Copyright (C) 1999-2024 Free Software Foundation, Inc.
This file is part of GDB.
This program 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 2 of the License, or
+ the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 59 Temple Place - Suite 330,
- Boston, MA 02111-1307, USA. */
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
-#include "defs.h"
-#include "obstack.h"
+#include "gdbsupport/gdb_obstack.h"
#include "bcache.h"
-#include "gdb_string.h" /* For memcpy declaration */
-
-/* Prototypes for local functions. */
-static unsigned int hash PARAMS ((void *, int));
+#include <algorithm>
-static void *lookup_cache PARAMS ((void *, int, int, struct bcache *));
+namespace gdb {
-/* FIXME: Incredibly simplistic hash generator. Probably way too expensive
- (consider long strings) and unlikely to have good distribution across hash
- values for typical input. */
+/* The type used to hold a single bcache string. The user data is
+ stored in d.data. Since it can be any type, it needs to have the
+ same alignment as the most strict alignment of any type on the host
+ machine. I don't know of any really correct way to do this in
+ stock ANSI C, so just do it the same way obstack.h does. */
-static unsigned int
-hash (bytes, count)
- void *bytes;
- int count;
+struct bstring
{
- unsigned int len;
- unsigned long hashval;
- unsigned int c;
- const unsigned char *data = bytes;
-
- hashval = 0;
- len = 0;
- while (count-- > 0)
- {
- c = *data++;
- hashval += c + (c << 17);
- hashval ^= hashval >> 2;
- ++len;
- }
- hashval += len + (len << 17);
- hashval ^= hashval >> 2;
- return (hashval % BCACHE_HASHSIZE);
-}
+ /* Hash chain. */
+ struct bstring *next;
+ /* Assume the data length is no more than 64k. */
+ unsigned short length;
+ /* The half hash hack. This contains the upper 16 bits of the hash
+ value and is used as a pre-check when comparing two strings and
+ avoids the need to do length or memcmp calls. It proves to be
+ roughly 100% effective. */
+ unsigned short half_hash;
+
+ union
+ {
+ char data[1];
+ double dummy;
+ }
+ d;
+};
-static void *
-lookup_cache (bytes, count, hashval, bcachep)
- void *bytes;
- int count;
- int hashval;
- struct bcache *bcachep;
+\f
+/* Growing the bcache's hash table. */
+
+/* If the average chain length grows beyond this, then we want to
+ resize our hash table. */
+#define CHAIN_LENGTH_THRESHOLD (5)
+
+void
+bcache::expand_hash_table ()
{
- void *location = NULL;
- struct hashlink **hashtablep;
- struct hashlink *linkp;
+ /* A table of good hash table sizes. Whenever we grow, we pick the
+ next larger size from this table. sizes[i] is close to 1 << (i+10),
+ so we roughly double the table size each time. After we fall off
+ the end of this table, we just double. Don't laugh --- there have
+ been executables sighted with a gigabyte of debug info. */
+ static const unsigned long sizes[] = {
+ 1021, 2053, 4099, 8191, 16381, 32771,
+ 65537, 131071, 262144, 524287, 1048573, 2097143,
+ 4194301, 8388617, 16777213, 33554467, 67108859, 134217757,
+ 268435459, 536870923, 1073741827, 2147483659UL
+ };
+ unsigned int new_num_buckets;
+ struct bstring **new_buckets;
+ unsigned int i;
+
+ /* Count the stats. Every unique item needs to be re-hashed and
+ re-entered. */
+ m_expand_count++;
+ m_expand_hash_count += m_unique_count;
+
+ /* Find the next size. */
+ new_num_buckets = m_num_buckets * 2;
+ for (unsigned long a_size : sizes)
+ if (a_size > m_num_buckets)
+ {
+ new_num_buckets = a_size;
+ break;
+ }
- hashtablep = bcachep->indextable[count];
- if (hashtablep != NULL)
+ /* Allocate the new table. */
+ {
+ size_t new_size = new_num_buckets * sizeof (new_buckets[0]);
+
+ new_buckets = (struct bstring **) xmalloc (new_size);
+ memset (new_buckets, 0, new_size);
+
+ m_structure_size -= m_num_buckets * sizeof (m_bucket[0]);
+ m_structure_size += new_size;
+ }
+
+ /* Rehash all existing strings. */
+ for (i = 0; i < m_num_buckets; i++)
{
- linkp = hashtablep[hashval];
- while (linkp != NULL)
+ struct bstring *s, *next;
+
+ for (s = m_bucket[i]; s; s = next)
{
- if (memcmp (BCACHE_DATA (linkp), bytes, count) == 0)
- {
- location = BCACHE_DATA (linkp);
- break;
- }
- linkp = linkp->next;
+ struct bstring **new_bucket;
+ next = s->next;
+
+ new_bucket = &new_buckets[(this->hash (&s->d.data, s->length)
+ % new_num_buckets)];
+ s->next = *new_bucket;
+ *new_bucket = s;
}
}
- return (location);
+
+ /* Plug in the new table. */
+ xfree (m_bucket);
+ m_bucket = new_buckets;
+ m_num_buckets = new_num_buckets;
}
-void *
-bcache (bytes, count, bcachep)
- void *bytes;
- int count;
- struct bcache *bcachep;
+\f
+/* Looking up things in the bcache. */
+
+/* The number of bytes needed to allocate a struct bstring whose data
+ is N bytes long. */
+#define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n))
+
+/* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has
+ never seen those bytes before, add a copy of them to BCACHE. In
+ either case, return a pointer to BCACHE's copy of that string. If
+ optional ADDED is not NULL, return 1 in case of new entry or 0 if
+ returning an old entry. */
+
+const void *
+bcache::insert (const void *addr, int length, bool *added)
{
- int hashval;
- void *location;
- struct hashlink *newlink;
- struct hashlink **linkpp;
- struct hashlink ***hashtablepp;
+ unsigned long full_hash;
+ unsigned short half_hash;
+ int hash_index;
+ struct bstring *s;
- if (count >= BCACHE_MAXLENGTH)
+ if (added != nullptr)
+ *added = false;
+
+ /* Lazily initialize the obstack. This can save quite a bit of
+ memory in some cases. */
+ if (m_total_count == 0)
{
- /* Rare enough to just stash unique copies */
- location = (void *) obstack_alloc (&bcachep->cache, count);
- bcachep->cache_bytes += count;
- memcpy (location, bytes, count);
- bcachep->bcache_overflows++;
+ /* We could use obstack_specify_allocation here instead, but
+ gdb_obstack.h specifies the allocation/deallocation
+ functions. */
+ obstack_init (&m_cache);
}
- else
+
+ /* If our average chain length is too high, expand the hash table. */
+ if (m_unique_count >= m_num_buckets * CHAIN_LENGTH_THRESHOLD)
+ expand_hash_table ();
+
+ m_total_count++;
+ m_total_size += length;
+
+ full_hash = this->hash (addr, length);
+
+ half_hash = (full_hash >> 16);
+ hash_index = full_hash % m_num_buckets;
+
+ /* Search the hash m_bucket for a string identical to the caller's.
+ As a short-circuit first compare the upper part of each hash
+ values. */
+ for (s = m_bucket[hash_index]; s; s = s->next)
{
- hashval = hash (bytes, count);
- location = lookup_cache (bytes, count, hashval, bcachep);
- if (location != NULL)
+ if (s->half_hash == half_hash)
{
- bcachep->cache_savings += count;
- bcachep->cache_hits++;
- }
- else
- {
- bcachep->cache_misses++;
- hashtablepp = &bcachep->indextable[count];
- if (*hashtablepp == NULL)
- {
- *hashtablepp = (struct hashlink **)
- obstack_alloc (&bcachep->cache, BCACHE_HASHSIZE * sizeof (struct hashlink *));
- bcachep->cache_bytes += BCACHE_HASHSIZE * sizeof (struct hashlink *);
- memset (*hashtablepp, 0, BCACHE_HASHSIZE * sizeof (struct hashlink *));
- }
- linkpp = &(*hashtablepp)[hashval];
- newlink = (struct hashlink *)
- obstack_alloc (&bcachep->cache, BCACHE_DATA_ALIGNMENT + count);
- bcachep->cache_bytes += BCACHE_DATA_ALIGNMENT + count;
- memcpy (BCACHE_DATA (newlink), bytes, count);
- newlink->next = *linkpp;
- *linkpp = newlink;
- location = BCACHE_DATA (newlink);
+ if (s->length == length
+ && this->compare (&s->d.data, addr, length))
+ return &s->d.data;
+ else
+ m_half_hash_miss_count++;
}
}
- return (location);
+
+ /* The user's string isn't in the list. Insert it after *ps. */
+ {
+ struct bstring *newobj
+ = (struct bstring *) obstack_alloc (&m_cache,
+ BSTRING_SIZE (length));
+
+ memcpy (&newobj->d.data, addr, length);
+ newobj->length = length;
+ newobj->next = m_bucket[hash_index];
+ newobj->half_hash = half_hash;
+ m_bucket[hash_index] = newobj;
+
+ m_unique_count++;
+ m_unique_size += length;
+ m_structure_size += BSTRING_SIZE (length);
+
+ if (added != nullptr)
+ *added = true;
+
+ return &newobj->d.data;
+ }
}
+\f
-void
-print_bcache_statistics (bcachep, id)
- struct bcache *bcachep;
- char *id;
+/* See bcache.h. */
+
+unsigned long
+bcache::hash (const void *addr, int length)
{
- struct hashlink **hashtablep;
- struct hashlink *linkp;
- int tidx, tcount, hidx, hcount, lcount, lmax, temp, lmaxt, lmaxh;
+ return fast_hash (addr, length, 0);
+}
- for (lmax = lcount = tcount = hcount = tidx = 0; tidx < BCACHE_MAXLENGTH; tidx++)
- {
- hashtablep = bcachep->indextable[tidx];
- if (hashtablep != NULL)
- {
- tcount++;
- for (hidx = 0; hidx < BCACHE_HASHSIZE; hidx++)
- {
- linkp = hashtablep[hidx];
- if (linkp != NULL)
- {
- hcount++;
- for (temp = 0; linkp != NULL; linkp = linkp->next)
- {
- lcount++;
- temp++;
- }
- if (temp > lmax)
- {
- lmax = temp;
- lmaxt = tidx;
- lmaxh = hidx;
- }
- }
- }
- }
- }
- printf_filtered (" Cached '%s' statistics:\n", id);
- printf_filtered (" Cache hits: %d\n", bcachep->cache_hits);
- printf_filtered (" Cache misses: %d\n", bcachep->cache_misses);
- printf_filtered (" Cache hit ratio: ");
- if (bcachep->cache_hits + bcachep->cache_misses > 0)
- {
- printf_filtered ("%d%%\n", ((bcachep->cache_hits) * 100) /
- (bcachep->cache_hits + bcachep->cache_misses));
- }
+/* See bcache.h. */
+
+int
+bcache::compare (const void *left, const void *right, int length)
+{
+ return memcmp (left, right, length) == 0;
+}
+
+/* Free all the storage associated with BCACHE. */
+bcache::~bcache ()
+{
+ /* Only free the obstack if we actually initialized it. */
+ if (m_total_count > 0)
+ obstack_free (&m_cache, 0);
+ xfree (m_bucket);
+}
+
+
+\f
+/* Printing statistics. */
+
+static void
+print_percentage (int portion, int total)
+{
+ if (total == 0)
+ /* i18n: Like "Percentage of duplicates, by count: (not applicable)". */
+ gdb_printf (_("(not applicable)\n"));
else
- {
- printf_filtered ("(not applicable)\n");
- }
- printf_filtered (" Space used for caching: %d\n", bcachep->cache_bytes);
- printf_filtered (" Space saved by cache hits: %d\n", bcachep->cache_savings);
- printf_filtered (" Number of bcache overflows: %d\n", bcachep->bcache_overflows);
- printf_filtered (" Number of index buckets used: %d\n", tcount);
- printf_filtered (" Number of hash table buckets used: %d\n", hcount);
- printf_filtered (" Number of chained items: %d\n", lcount);
- printf_filtered (" Average hash table population: ");
- if (tcount > 0)
- {
- printf_filtered ("%d%%\n", (hcount * 100) / (tcount * BCACHE_HASHSIZE));
- }
+ gdb_printf ("%3d%%\n", (int) (portion * 100.0 / total));
+}
+
+
+/* Print statistics on BCACHE's memory usage and efficacity at
+ eliminating duplication. NAME should describe the kind of data
+ BCACHE holds. Statistics are printed using `gdb_printf' and
+ its ilk. */
+void
+bcache::print_statistics (const char *type)
+{
+ int occupied_buckets;
+ int max_chain_length;
+ int median_chain_length;
+ int max_entry_size;
+ int median_entry_size;
+
+ /* Count the number of occupied buckets, tally the various string
+ lengths, and measure chain lengths. */
+ {
+ unsigned int b;
+ int *chain_length = XCNEWVEC (int, m_num_buckets + 1);
+ int *entry_size = XCNEWVEC (int, m_unique_count + 1);
+ int stringi = 0;
+
+ occupied_buckets = 0;
+
+ for (b = 0; b < m_num_buckets; b++)
+ {
+ struct bstring *s = m_bucket[b];
+
+ chain_length[b] = 0;
+
+ if (s)
+ {
+ occupied_buckets++;
+
+ while (s)
+ {
+ gdb_assert (b < m_num_buckets);
+ chain_length[b]++;
+ gdb_assert (stringi < m_unique_count);
+ entry_size[stringi++] = s->length;
+ s = s->next;
+ }
+ }
+ }
+
+ /* To compute the median, we need the set of chain lengths
+ sorted. */
+ std::sort (chain_length, chain_length + m_num_buckets);
+ std::sort (entry_size, entry_size + m_unique_count);
+
+ if (m_num_buckets > 0)
+ {
+ max_chain_length = chain_length[m_num_buckets - 1];
+ median_chain_length = chain_length[m_num_buckets / 2];
+ }
+ else
+ {
+ max_chain_length = 0;
+ median_chain_length = 0;
+ }
+ if (m_unique_count > 0)
+ {
+ max_entry_size = entry_size[m_unique_count - 1];
+ median_entry_size = entry_size[m_unique_count / 2];
+ }
+ else
+ {
+ max_entry_size = 0;
+ median_entry_size = 0;
+ }
+
+ xfree (chain_length);
+ xfree (entry_size);
+ }
+
+ gdb_printf (_(" M_Cached '%s' statistics:\n"), type);
+ gdb_printf (_(" Total object count: %ld\n"), m_total_count);
+ gdb_printf (_(" Unique object count: %lu\n"), m_unique_count);
+ gdb_printf (_(" Percentage of duplicates, by count: "));
+ print_percentage (m_total_count - m_unique_count, m_total_count);
+ gdb_printf ("\n");
+
+ gdb_printf (_(" Total object size: %ld\n"), m_total_size);
+ gdb_printf (_(" Unique object size: %ld\n"), m_unique_size);
+ gdb_printf (_(" Percentage of duplicates, by size: "));
+ print_percentage (m_total_size - m_unique_size, m_total_size);
+ gdb_printf ("\n");
+
+ gdb_printf (_(" Max entry size: %d\n"), max_entry_size);
+ gdb_printf (_(" Average entry size: "));
+ if (m_unique_count > 0)
+ gdb_printf ("%ld\n", m_unique_size / m_unique_count);
else
- {
- printf_filtered ("(not applicable)\n");
- }
- printf_filtered (" Average chain length ");
- if (hcount > 0)
- {
- printf_filtered ("%d\n", lcount / hcount);
- }
+ /* i18n: "Average entry size: (not applicable)". */
+ gdb_printf (_("(not applicable)\n"));
+ gdb_printf (_(" Median entry size: %d\n"), median_entry_size);
+ gdb_printf ("\n");
+
+ gdb_printf (_(" \
+Total memory used by bcache, including overhead: %ld\n"),
+ m_structure_size);
+ gdb_printf (_(" Percentage memory overhead: "));
+ print_percentage (m_structure_size - m_unique_size, m_unique_size);
+ gdb_printf (_(" Net memory savings: "));
+ print_percentage (m_total_size - m_structure_size, m_total_size);
+ gdb_printf ("\n");
+
+ gdb_printf (_(" Hash table size: %3d\n"),
+ m_num_buckets);
+ gdb_printf (_(" Hash table expands: %lu\n"),
+ m_expand_count);
+ gdb_printf (_(" Hash table hashes: %lu\n"),
+ m_total_count + m_expand_hash_count);
+ gdb_printf (_(" Half hash misses: %lu\n"),
+ m_half_hash_miss_count);
+ gdb_printf (_(" Hash table population: "));
+ print_percentage (occupied_buckets, m_num_buckets);
+ gdb_printf (_(" Median hash chain length: %3d\n"),
+ median_chain_length);
+ gdb_printf (_(" Average hash chain length: "));
+ if (m_num_buckets > 0)
+ gdb_printf ("%3lu\n", m_unique_count / m_num_buckets);
else
- {
- printf_filtered ("(not applicable)\n");
- }
- printf_filtered (" Maximum chain length %d at %d:%d\n", lmax, lmaxt, lmaxh);
+ /* i18n: "Average hash chain length: (not applicable)". */
+ gdb_printf (_("(not applicable)\n"));
+ gdb_printf (_(" Maximum hash chain length: %3d\n"),
+ max_chain_length);
+ gdb_printf ("\n");
}
+
+int
+bcache::memory_used ()
+{
+ if (m_total_count == 0)
+ return 0;
+ return obstack_memory_used (&m_cache);
+}
+
+} /* namespace gdb */
projects / thirdparty / binutils-gdb.git / blobdiff