[PATCH 21/38] Use htab_up in abbrev_table

[Tom Tromey <tom@tromey.com>]

This changes abbrev_table to use an htab_up rather than an ad hoc,
bucket-based hash table.

2020-01-22  Tom Tromey  <tom@tromey.com>

	* dwarf2/abbrev.c (abbrev_table): Move constructor from header.
	Rewrite.
	(abbrev_table::add_abbrev, abbrev_table::lookup_abbrev): Rewrite.
	* dwarf2/abbrev.h (struct abbrev_info) <next>: Remove.
	(abbrev_table::abbrev_table): No longer inline.
	(ABBREV_HASH_SIZE): Remove.
	(abbrev_table::m_abbrevs): Now an htab_up.

Change-Id: Icbaa8e49501f9c43218d6a81a7e8c4d3a77d65dc
---
 gdb/ChangeLog       | 10 ++++++++++
 gdb/dwarf2/abbrev.c | 48 +++++++++++++++++++++++++++++----------------
 gdb/dwarf2/abbrev.h | 19 +++---------------
 3 files changed, 44 insertions(+), 33 deletions(-)

diff --git a/gdb/dwarf2/abbrev.c b/gdb/dwarf2/abbrev.c
index fac7309b93c..f843e32d950 100644
--- a/gdb/dwarf2/abbrev.c
+++ b/gdb/dwarf2/abbrev.c
@@ -30,6 +30,25 @@
 #include "dwarf2/leb.h"
 #include "bfd.h"
 
+/* Hash function for an abbrev.  */
+
+static hashval_t
+hash_abbrev (const void *item)
+{
+  const struct abbrev_info *info = (const struct abbrev_info *) item;
+  return info->number;
+}
+
+/* Comparison function for abbrevs.  */
+
+static int
+eq_abbrev (const void *lhs, const void *rhs)
+{
+  const struct abbrev_info *l_info = (const struct abbrev_info *) lhs;
+  const struct abbrev_info *r_info = (const struct abbrev_info *) rhs;
+  return l_info->number == r_info->number;
+}
+
 /* Abbreviation tables.
 
    In DWARF version 2, the description of the debugging information is
@@ -37,6 +56,13 @@
    dies from a section we read in all abbreviations and install them
    in a hash table.  */
 
+abbrev_table::abbrev_table (sect_offset off)
+  : sect_off (off),
+    m_abbrevs (htab_create_alloc (20, hash_abbrev, eq_abbrev,
+				  nullptr, xcalloc, xfree))
+{
+}
+
 /* Allocate space for a struct abbrev_info object in ABBREV_TABLE.  */
 
 struct abbrev_info *
@@ -56,11 +82,8 @@ void
 abbrev_table::add_abbrev (unsigned int abbrev_number,
 			  struct abbrev_info *abbrev)
 {
-  unsigned int hash_number;
-
-  hash_number = abbrev_number % ABBREV_HASH_SIZE;
-  abbrev->next = m_abbrevs[hash_number];
-  m_abbrevs[hash_number] = abbrev;
+  void **slot = htab_find_slot (m_abbrevs.get (), abbrev, INSERT);
+  *slot = abbrev;
 }
 
 /* Look up an abbrev in the table.
@@ -69,19 +92,10 @@ abbrev_table::add_abbrev (unsigned int abbrev_number,
 struct abbrev_info *
 abbrev_table::lookup_abbrev (unsigned int abbrev_number)
 {
-  unsigned int hash_number;
-  struct abbrev_info *abbrev;
-
-  hash_number = abbrev_number % ABBREV_HASH_SIZE;
-  abbrev = m_abbrevs[hash_number];
+  struct abbrev_info search;
+  search.number = abbrev_number;
 
-  while (abbrev)
-    {
-      if (abbrev->number == abbrev_number)
-	return abbrev;
-      abbrev = abbrev->next;
-    }
-  return NULL;
+  return (struct abbrev_info *) htab_find (m_abbrevs.get (), &search);
 }
 
 /* Read in an abbrev table.  */
diff --git a/gdb/dwarf2/abbrev.h b/gdb/dwarf2/abbrev.h
index 52103b0a683..b9ace64b448 100644
--- a/gdb/dwarf2/abbrev.h
+++ b/gdb/dwarf2/abbrev.h
@@ -35,7 +35,6 @@ struct abbrev_info
     unsigned short has_children;		/* boolean */
     unsigned short num_attrs;	/* number of attributes */
     struct attr_abbrev *attrs;	/* an array of attribute descriptions */
-    struct abbrev_info *next;	/* next in chain */
   };
 
 struct attr_abbrev
@@ -47,9 +46,6 @@ struct attr_abbrev
     LONGEST implicit_const;
   };
 
-/* Size of abbrev_table.abbrev_hash_table.  */
-#define ABBREV_HASH_SIZE 121
-
 struct abbrev_table;
 typedef std::unique_ptr<struct abbrev_table> abbrev_table_up;
 
@@ -73,13 +69,7 @@ struct abbrev_table
 
 private:
 
-  explicit abbrev_table (sect_offset off)
-    : sect_off (off)
-  {
-    m_abbrevs =
-      XOBNEWVEC (&m_abbrev_obstack, struct abbrev_info *, ABBREV_HASH_SIZE);
-    memset (m_abbrevs, 0, ABBREV_HASH_SIZE * sizeof (struct abbrev_info *));
-  }
+  explicit abbrev_table (sect_offset off);
 
   DISABLE_COPY_AND_ASSIGN (abbrev_table);
 
@@ -90,11 +80,8 @@ private:
   /* Add an abbreviation to the table.  */
   void add_abbrev (unsigned int abbrev_number, struct abbrev_info *abbrev);
 
-  /* Hash table of abbrevs.
-     This is an array of size ABBREV_HASH_SIZE allocated in abbrev_obstack.
-     It could be statically allocated, but the previous code didn't so we
-     don't either.  */
-  struct abbrev_info **m_abbrevs;
+  /* Hash table of abbrevs.  */
+  htab_up m_abbrevs;
 
   /* Storage for the abbrev table.  */
   auto_obstack m_abbrev_obstack;
-- 
2.17.2