X-Git-Url: http://drtracing.org/?a=blobdiff_plain;f=gdb%2Fbcache.c;h=f3abc12a10e2351db126c4da253865ee707d71e1;hb=e81d5d059b485b37a6f8cfb44e563ad8b702df07;hp=97485ddda3a71ddc16406e1916b85aeca1567c7d;hpb=30727aa6d12fb866494020c0b62ab265a2bdcdfe;p=deliverable%2Fbinutils-gdb.git

diff --git a/gdb/bcache.c b/gdb/bcache.c
index 97485ddda3..f3abc12a10 100644
--- a/gdb/bcache.c
+++ b/gdb/bcache.c
@@ -1,12 +1,14 @@
 /* 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) 1999-2015 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,
@@ -15,202 +17,474 @@
    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 "gdb_obstack.h"
 #include "bcache.h"
-#include "gdb_string.h"		/* For memcpy declaration */
 
-/* Prototypes for local functions. */
+/* 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.  */
+
+struct bstring
+{
+  /* 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 unsigned int hash PARAMS ((void *, int));
 
-static void *lookup_cache PARAMS ((void *, int, int, struct bcache *));
+/* The structure for a bcache itself.  The bcache is initialized, in
+   bcache_xmalloc(), by filling it with zeros and then setting the
+   corresponding obstack's malloc() and free() methods.  */
+
+struct bcache
+{
+  /* All the bstrings are allocated here.  */
+  struct obstack cache;
+
+  /* How many hash buckets we're using.  */
+  unsigned int num_buckets;
+  
+  /* Hash buckets.  This table is allocated using malloc, so when we
+     grow the table we can return the old table to the system.  */
+  struct bstring **bucket;
+
+  /* Statistics.  */
+  unsigned long unique_count;	/* number of unique strings */
+  long total_count;	/* total number of strings cached, including dups */
+  long unique_size;	/* size of unique strings, in bytes */
+  long total_size;      /* total number of bytes cached, including dups */
+  long structure_size;	/* total size of bcache, including infrastructure */
+  /* Number of times that the hash table is expanded and hence
+     re-built, and the corresponding number of times that a string is
+     [re]hashed as part of entering it into the expanded table.  The
+     total number of hashes can be computed by adding TOTAL_COUNT to
+     expand_hash_count.  */
+  unsigned long expand_count;
+  unsigned long expand_hash_count;
+  /* Number of times that the half-hash compare hit (compare the upper
+     16 bits of hash values) hit, but the corresponding combined
+     length/data compare missed.  */
+  unsigned long half_hash_miss_count;
+
+  /* Hash function to be used for this bcache object.  */
+  unsigned long (*hash_function)(const void *addr, int length);
+
+  /* Compare function to be used for this bcache object.  */
+  int (*compare_function)(const void *, const void *, int length);
+};
+
+/* The old hash function was stolen from SDBM. This is what DB 3.0
+   uses now, and is better than the old one.  */
+
+unsigned long
+hash(const void *addr, int length)
+{
+  return hash_continue (addr, length, 0);
+}
 
-/* FIXME:  Incredibly simplistic hash generator.  Probably way too expensive
-   (consider long strings) and unlikely to have good distribution across hash
-   values for typical input. */
+/* Continue the calculation of the hash H at the given address.  */
 
-static unsigned int
-hash (bytes, count)
-     void *bytes;
-     int count;
+unsigned long
+hash_continue (const void *addr, int length, unsigned long h)
 {
-  unsigned int len;
-  unsigned long hashval;
-  unsigned int c;
-  const unsigned char *data = bytes;
-
-  hashval = 0;
-  len = 0;
-  while (count-- > 0)
+  const unsigned char *k, *e;
+
+  k = (const unsigned char *)addr;
+  e = k+length;
+  for (; k< e;++k)
     {
-      c = *data++;
-      hashval += c + (c << 17);
-      hashval ^= hashval >> 2;
-      ++len;
+      h *=16777619;
+      h ^= *k;
     }
-  hashval += len + (len << 17);
-  hashval ^= hashval >> 2;
-  return (hashval % BCACHE_HASHSIZE);
+  return (h);
 }
+
+/* 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)
 
-static void *
-lookup_cache (bytes, count, hashval, bcachep)
-     void *bytes;
-     int count;
-     int hashval;
-     struct bcache *bcachep;
+static void
+expand_hash_table (struct bcache *bcache)
 {
-  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 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.  */
+  bcache->expand_count++;
+  bcache->expand_hash_count += bcache->unique_count;
+
+  /* Find the next size.  */
+  new_num_buckets = bcache->num_buckets * 2;
+  for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++)
+    if (sizes[i] > bcache->num_buckets)
+      {
+	new_num_buckets = sizes[i];
+	break;
+      }
+
+  /* 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);
 
-  hashtablep = bcachep->indextable[count];
-  if (hashtablep != NULL)
+    bcache->structure_size -= (bcache->num_buckets
+			       * sizeof (bcache->bucket[0]));
+    bcache->structure_size += new_size;
+  }
+
+  /* Rehash all existing strings.  */
+  for (i = 0; i < bcache->num_buckets; i++)
     {
-      linkp = hashtablep[hashval];
-      while (linkp != NULL)
+      struct bstring *s, *next;
+
+      for (s = bcache->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[(bcache->hash_function (&s->d.data,
+							    s->length)
+				     % new_num_buckets)];
+	  s->next = *new_bucket;
+	  *new_bucket = s;
 	}
     }
-  return (location);
+
+  /* Plug in the new table.  */
+  if (bcache->bucket)
+    xfree (bcache->bucket);
+  bcache->bucket = new_buckets;
+  bcache->num_buckets = new_num_buckets;
 }
 
-void *
-bcache (bytes, count, bcachep)
-     void *bytes;
-     int count;
-     struct bcache *bcachep;
+
+/* 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.  */
+const void *
+bcache (const void *addr, int length, struct bcache *cache)
 {
-  int hashval;
-  void *location;
-  struct hashlink *newlink;
-  struct hashlink **linkpp;
-  struct hashlink ***hashtablepp;
+  return bcache_full (addr, length, cache, NULL);
+}
+
+/* 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_full (const void *addr, int length, struct bcache *bcache, int *added)
+{
+  unsigned long full_hash;
+  unsigned short half_hash;
+  int hash_index;
+  struct bstring *s;
+
+  if (added)
+    *added = 0;
 
-  if (count >= BCACHE_MAXLENGTH)
+  /* Lazily initialize the obstack.  This can save quite a bit of
+     memory in some cases.  */
+  if (bcache->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 (&bcache->cache);
     }
-  else
+
+  /* If our average chain length is too high, expand the hash table.  */
+  if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD)
+    expand_hash_table (bcache);
+
+  bcache->total_count++;
+  bcache->total_size += length;
+
+  full_hash = bcache->hash_function (addr, length);
+
+  half_hash = (full_hash >> 16);
+  hash_index = full_hash % bcache->num_buckets;
+
+  /* Search the hash bucket for a string identical to the caller's.
+     As a short-circuit first compare the upper part of each hash
+     values.  */
+  for (s = bcache->bucket[hash_index]; s; s = s->next)
     {
-      hashval = hash (bytes, count);
-      location = lookup_cache (bytes, count, hashval, bcachep);
-      if (location != NULL)
-	{
-	  bcachep->cache_savings += count;
-	  bcachep->cache_hits++;
-	}
-      else
+      if (s->half_hash == half_hash)
 	{
-	  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
+	      && bcache->compare_function (&s->d.data, addr, length))
+	    return &s->d.data;
+	  else
+	    bcache->half_hash_miss_count++;
 	}
     }
-  return (location);
+
+  /* The user's string isn't in the list.  Insert it after *ps.  */
+  {
+    struct bstring *newobj
+      = obstack_alloc (&bcache->cache, BSTRING_SIZE (length));
+
+    memcpy (&newobj->d.data, addr, length);
+    newobj->length = length;
+    newobj->next = bcache->bucket[hash_index];
+    newobj->half_hash = half_hash;
+    bcache->bucket[hash_index] = newobj;
+
+    bcache->unique_count++;
+    bcache->unique_size += length;
+    bcache->structure_size += BSTRING_SIZE (length);
+
+    if (added)
+      *added = 1;
+
+    return &newobj->d.data;
+  }
 }
+
+
+/* Compare the byte string at ADDR1 of lenght LENGHT to the
+   string at ADDR2.  Return 1 if they are equal.  */
+
+static int
+bcache_compare (const void *addr1, const void *addr2, int length)
+{
+  return memcmp (addr1, addr2, length) == 0;
+}
+
+/* Allocating and freeing bcaches.  */
+
+/* Allocated a bcache.  HASH_FUNCTION and COMPARE_FUNCTION can be used
+   to pass in custom hash, and compare functions to be used by this
+   bcache.  If HASH_FUNCTION is NULL hash() is used and if
+   COMPARE_FUNCTION is NULL memcmp() is used.  */
 
+struct bcache *
+bcache_xmalloc (unsigned long (*hash_function)(const void *, int length),
+                int (*compare_function)(const void *, 
+					const void *, 
+					int length))
+{
+  /* Allocate the bcache pre-zeroed.  */
+  struct bcache *b = XCNEW (struct bcache);
+
+  if (hash_function)
+    b->hash_function = hash_function;
+  else
+    b->hash_function = hash;
+
+  if (compare_function)
+    b->compare_function = compare_function;
+  else
+    b->compare_function = bcache_compare;
+  return b;
+}
+
+/* Free all the storage associated with BCACHE.  */
 void
-print_bcache_statistics (bcachep, id)
-     struct bcache *bcachep;
-     char *id;
+bcache_xfree (struct bcache *bcache)
 {
-  struct hashlink **hashtablep;
-  struct hashlink *linkp;
-  int tidx, tcount, hidx, hcount, lcount, lmax, temp, lmaxt, lmaxh;
+  if (bcache == NULL)
+    return;
+  /* Only free the obstack if we actually initialized it.  */
+  if (bcache->total_count > 0)
+    obstack_free (&bcache->cache, 0);
+  xfree (bcache->bucket);
+  xfree (bcache);
+}
 
-  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));
-    }
+
+
+/* Printing statistics.  */
+
+static void
+print_percentage (int portion, int total)
+{
+  if (total == 0)
+    /* i18n: Like "Percentage of duplicates, by count: (not applicable)".  */
+    printf_filtered (_("(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));
-    }
+    printf_filtered ("%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 `printf_filtered' and
+   its ilk.  */
+void
+print_bcache_statistics (struct bcache *c, 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, c->num_buckets + 1);
+    int *entry_size = XCNEWVEC (int, c->unique_count + 1);
+    int stringi = 0;
+
+    occupied_buckets = 0;
+
+    for (b = 0; b < c->num_buckets; b++)
+      {
+	struct bstring *s = c->bucket[b];
+
+	chain_length[b] = 0;
+
+	if (s)
+	  {
+	    occupied_buckets++;
+	    
+	    while (s)
+	      {
+		gdb_assert (b < c->num_buckets);
+		chain_length[b]++;
+		gdb_assert (stringi < c->unique_count);
+		entry_size[stringi++] = s->length;
+		s = s->next;
+	      }
+	  }
+      }
+
+    /* To compute the median, we need the set of chain lengths
+       sorted.  */
+    qsort (chain_length, c->num_buckets, sizeof (chain_length[0]),
+	   compare_positive_ints);
+    qsort (entry_size, c->unique_count, sizeof (entry_size[0]),
+	   compare_positive_ints);
+
+    if (c->num_buckets > 0)
+      {
+	max_chain_length = chain_length[c->num_buckets - 1];
+	median_chain_length = chain_length[c->num_buckets / 2];
+      }
+    else
+      {
+	max_chain_length = 0;
+	median_chain_length = 0;
+      }
+    if (c->unique_count > 0)
+      {
+	max_entry_size = entry_size[c->unique_count - 1];
+	median_entry_size = entry_size[c->unique_count / 2];
+      }
+    else
+      {
+	max_entry_size = 0;
+	median_entry_size = 0;
+      }
+
+    xfree (chain_length);
+    xfree (entry_size);
+  }
+
+  printf_filtered (_("  Cached '%s' statistics:\n"), type);
+  printf_filtered (_("    Total object count:  %ld\n"), c->total_count);
+  printf_filtered (_("    Unique object count: %lu\n"), c->unique_count);
+  printf_filtered (_("    Percentage of duplicates, by count: "));
+  print_percentage (c->total_count - c->unique_count, c->total_count);
+  printf_filtered ("\n");
+
+  printf_filtered (_("    Total object size:   %ld\n"), c->total_size);
+  printf_filtered (_("    Unique object size:  %ld\n"), c->unique_size);
+  printf_filtered (_("    Percentage of duplicates, by size:  "));
+  print_percentage (c->total_size - c->unique_size, c->total_size);
+  printf_filtered ("\n");
+
+  printf_filtered (_("    Max entry size:     %d\n"), max_entry_size);
+  printf_filtered (_("    Average entry size: "));
+  if (c->unique_count > 0)
+    printf_filtered ("%ld\n", c->unique_size / c->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)".  */
+    printf_filtered (_("(not applicable)\n"));    
+  printf_filtered (_("    Median entry size:  %d\n"), median_entry_size);
+  printf_filtered ("\n");
+
+  printf_filtered (_("    \
+Total memory used by bcache, including overhead: %ld\n"),
+		   c->structure_size);
+  printf_filtered (_("    Percentage memory overhead: "));
+  print_percentage (c->structure_size - c->unique_size, c->unique_size);
+  printf_filtered (_("    Net memory savings:         "));
+  print_percentage (c->total_size - c->structure_size, c->total_size);
+  printf_filtered ("\n");
+
+  printf_filtered (_("    Hash table size:           %3d\n"), 
+		   c->num_buckets);
+  printf_filtered (_("    Hash table expands:        %lu\n"),
+		   c->expand_count);
+  printf_filtered (_("    Hash table hashes:         %lu\n"),
+		   c->total_count + c->expand_hash_count);
+  printf_filtered (_("    Half hash misses:          %lu\n"),
+		   c->half_hash_miss_count);
+  printf_filtered (_("    Hash table population:     "));
+  print_percentage (occupied_buckets, c->num_buckets);
+  printf_filtered (_("    Median hash chain length:  %3d\n"),
+		   median_chain_length);
+  printf_filtered (_("    Average hash chain length: "));
+  if (c->num_buckets > 0)
+    printf_filtered ("%3lu\n", c->unique_count / c->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)".  */
+    printf_filtered (_("(not applicable)\n"));
+  printf_filtered (_("    Maximum hash chain length: %3d\n"), 
+		   max_chain_length);
+  printf_filtered ("\n");
+}
+
+int
+bcache_memory_used (struct bcache *bcache)
+{
+  if (bcache->total_count == 0)
+    return 0;
+  return obstack_memory_used (&bcache->cache);
 }