Replace hash function from bcache with fast_hash

This function is not just slower than xxhash, it is slower than
even libiberty's iterative_hash, so there does not seem to be
a reason for it to exist.

------------------------------------------------------------
Benchmark                     Time           CPU Iterations
------------------------------------------------------------
BM_xxh3                      11 ns         11 ns   66127192
BM_xxh32                     19 ns         19 ns   36792609
BM_xxh64                     16 ns         16 ns   42941328
BM_city32                    26 ns         26 ns   27028370
BM_city64                    17 ns         17 ns   40472793
BM_iterative_hash            77 ns         77 ns    9088854
BM_bcache_hash              125 ns        125 ns    5599232

gdb/ChangeLog:

2019-12-03  Christian Biesinger  <cbiesinger@google.com>

	* bcache.c (hash): Remove.
	(hash_continue): Remove.
	* bcache.h (hash): Remove.
	(hash_continue): Remove.
	(struct bcache) <ctor>: Update.
	* psymtab.c (psymbol_hash): Update.
	* stabsread.c (hashname): Update.
	* utils.h (fast_hash): Add an argument for a start value,
	defaulting to zero.

Change-Id: I107f013eda5fdd3293326b5a206be43155dae0f8

1 files changed, 8 insertions, 7 deletions

diff --git a/gdb/bcache.h b/gdb/bcache.h
index 15dcc63440f..f26f79dca39 100644
--- a/gdb/bcache.h
+++ b/gdb/bcache.h
@@ -138,23 +138,18 @@
 
 struct bstring;
 
-/* The hash functions */
-extern unsigned long hash (const void *addr, int length);
-extern unsigned long hash_continue (const void *addr, int length,
-                                    unsigned long h);
-
 struct bcache
 {
   /* Allocate a bcache.  HASH_FN and COMPARE_FN 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
+     HASH_FUNCTION is NULL fast_hash() is used and if COMPARE_FUNCTION is
      NULL memcmp() is used.  */
 
   explicit bcache (unsigned long (*hash_fn)(const void *,
 					    int length) = nullptr,
 		   int (*compare_fn)(const void *, const void *,
 				     int length) = nullptr)
-    : m_hash_function (hash_fn == nullptr ? hash : hash_fn),
+    : m_hash_function (hash_fn == nullptr ? default_hash : hash_fn),
       m_compare_function (compare_fn == nullptr ? compare : compare_fn)
   {
   }
@@ -217,6 +212,12 @@ private:
   /* Default compare function.  */
   static int compare (const void *addr1, const void *addr2, int length);
 
+  /* Default hash function.  */
+  static unsigned long default_hash (const void *ptr, int length)
+  {
+    return fast_hash (ptr, length, 0);
+  }
+
   /* Expand the hash table.  */
   void expand_hash_table ();
 };