From 4cbd39b289b012782df2fdda9adc7eacdcfc6ad7 Mon Sep 17 00:00:00 2001 From: Christian Biesinger Date: Mon, 2 Dec 2019 18:58:35 -0600 Subject: [PATCH] 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 * bcache.c (hash): Remove. (hash_continue): Remove. * bcache.h (hash): Remove. (hash_continue): Remove. (struct bcache) : 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 --- gdb/ChangeLog | 12 ++++++++++++ gdb/bcache.c | 25 ------------------------- gdb/bcache.h | 15 ++++++++------- gdb/psymtab.c | 11 +++++------ gdb/stabsread.c | 2 +- gdb/utils.h | 11 ++++++----- 6 files changed, 32 insertions(+), 44 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 5ece6883523..d12bd1c5a57 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,15 @@ +2019-12-03 Christian Biesinger + + * bcache.c (hash): Remove. + (hash_continue): Remove. + * bcache.h (hash): Remove. + (hash_continue): Remove. + (struct bcache) : Update. + * psymtab.c (psymbol_hash): Update. + * stabsread.c (hashname): Update. + * utils.h (fast_hash): Add an argument for a start value, + defaulting to zero. + 2019-12-03 Philippe Waroquiers * symtab.c (symbol_cache_clear_slot): Move close to cleared type. (destroy_block_symbol_cache): New function. diff --git a/gdb/bcache.c b/gdb/bcache.c index 3f0a63be229..497efe96cbf 100644 --- a/gdb/bcache.c +++ b/gdb/bcache.c @@ -51,31 +51,6 @@ struct bstring d; }; -/* 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); -} - -/* Continue the calculation of the hash H at the given address. */ - -unsigned long -hash_continue (const void *addr, int length, unsigned long h) -{ - const unsigned char *k, *e; - - k = (const unsigned char *)addr; - e = k+length; - for (; k< e;++k) - { - h *=16777619; - h ^= *k; - } - return (h); -} /* Growing the bcache's hash table. */ 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 (); }; diff --git a/gdb/psymtab.c b/gdb/psymtab.c index 7074a32956a..2cbc6d4f65f 100644 --- a/gdb/psymtab.c +++ b/gdb/psymtab.c @@ -1530,14 +1530,13 @@ psymbol_hash (const void *addr, int length) unsigned int domain = psymbol->domain; unsigned int theclass = psymbol->aclass; - h = hash_continue (&psymbol->ginfo.value, sizeof (psymbol->ginfo.value), h); - h = hash_continue (&lang, sizeof (unsigned int), h); - h = hash_continue (&domain, sizeof (unsigned int), h); - h = hash_continue (&theclass, sizeof (unsigned int), h); + h = fast_hash (&psymbol->ginfo.value, sizeof (psymbol->ginfo.value), h); + h = fast_hash (&lang, sizeof (unsigned int), h); + h = fast_hash (&domain, sizeof (unsigned int), h); + h = fast_hash (&theclass, sizeof (unsigned int), h); /* Note that psymbol names are interned via symbol_set_names, so there's no need to hash the contents of the name here. */ - h = hash_continue (&psymbol->ginfo.name, - sizeof (psymbol->ginfo.name), h); + h = fast_hash (&psymbol->ginfo.name, sizeof (psymbol->ginfo.name), h); return h; } diff --git a/gdb/stabsread.c b/gdb/stabsread.c index 979df0266cf..91a73dd10db 100644 --- a/gdb/stabsread.c +++ b/gdb/stabsread.c @@ -4778,7 +4778,7 @@ find_name_end (const char *name) int hashname (const char *name) { - return hash (name, strlen (name)) % HASHSIZE; + return fast_hash (name, strlen (name)) % HASHSIZE; } /* Initializer for this module. */ diff --git a/gdb/utils.h b/gdb/utils.h index 79c8a6fc8d8..c8337f23017 100644 --- a/gdb/utils.h +++ b/gdb/utils.h @@ -571,17 +571,18 @@ extern void copy_bitwise (gdb_byte *dest, ULONGEST dest_offset, const gdb_byte *source, ULONGEST source_offset, ULONGEST nbits, int bits_big_endian); -/* A fast hashing function. This can be used to hash strings in a fast way +/* A fast hashing function. This can be used to hash data in a fast way when the length is known. If no fast hashing library is available, falls - back to iterative_hash from libiberty. */ + back to iterative_hash from libiberty. START_VALUE can be set to + continue hashing from a previous value. */ static inline unsigned int -fast_hash (const char* str, size_t len) +fast_hash (const void *ptr, size_t len, unsigned int start_value = 0) { #ifdef HAVE_LIBXXHASH - return XXH64 (str, len, 0); + return XXH64 (ptr, len, start_value); #else - return iterative_hash (str, len, 0); + return iterative_hash (ptr, len, start_value); #endif } -- 2.39.5