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Precompute hash only once when interning string literals

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When a fake string is interned, use the capa field to store the string
hash. This lets us compute it once for hash lookup and embedding the
hash in the interned string.

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>
This commit is contained in:
Étienne Barrié 2024-11-04 11:41:04 +01:00 committed by Jean Boussier
parent 09874e90bf
commit 1e037108a1
Notes: git 2024-11-04 13:37:33 +00:00 
Merged: https://github.com/ruby/ruby/pull/11989
1 changed files with 26 additions and 6 deletions
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32
string.c
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@ -352,9 +352,24 @@ static int fstring_cmp(VALUE a, VALUE b);
static VALUE register_fstring(VALUE str, bool copy, bool precompute_hash);
#if SIZEOF_LONG == SIZEOF_VOIDP
static st_index_t
fstring_hash(VALUE str)
{
if (FL_TEST_RAW(str, STR_FAKESTR)) {
// register_fstring precomputes the hash and stores it in capa for fake strings
return (st_index_t)RSTRING(str)->as.heap.aux.capa;
}
else {
return rb_str_hash(str);
}
}
#else
#define fstring_hash rb_str_hash
#endif
const struct st_hash_type rb_fstring_hash_type = {
fstring_cmp,
rb_str_hash,
fstring_hash,
};
#define BARE_STRING_P(str) (!FL_ANY_RAW(str, FL_EXIVAR) && RBASIC_CLASS(str) == rb_cString)
@ -371,7 +386,7 @@ str_do_hash(VALUE str)
}
static VALUE
str_precompute_hash(VALUE str)
str_store_precomputed_hash(VALUE str, st_index_t hash)
{
RUBY_ASSERT(!FL_TEST_RAW(str, STR_PRECOMPUTED_HASH));
RUBY_ASSERT(STR_EMBED_P(str));
@ -382,7 +397,6 @@ str_precompute_hash(VALUE str)
RUBY_ASSERT(free_bytes >= sizeof(st_index_t));
#endif
st_index_t hash = str_do_hash(str);
memcpy(RSTRING_END(str) + TERM_LEN(str), &hash, sizeof(hash));
FL_SET(str, STR_PRECOMPUTED_HASH);
@ -399,7 +413,6 @@ struct fstr_update_arg {
static int
fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t data, int existing)
{
struct fstr_update_arg *arg = (struct fstr_update_arg *)data;
VALUE str = (VALUE)*key;
@ -429,7 +442,7 @@ fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t data, int exist
STR_SET_LEN(new_str, RSTRING_LEN(str));
TERM_FILL(RSTRING_END(new_str), TERM_LEN(str));
rb_enc_copy(new_str, str);
str_precompute_hash(new_str);
str_store_precomputed_hash(new_str, fstring_hash(str));
}
else {
new_str = str_new(rb_cString, RSTRING(str)->as.heap.ptr, RSTRING(str)->len);
@ -509,6 +522,14 @@ register_fstring(VALUE str, bool copy, bool precompute_hash)
.precompute_hash = precompute_hash
};
#if SIZEOF_VOIDP == SIZEOF_LONG
if (FL_TEST_RAW(str, STR_FAKESTR)) {
// if the string hasn't been interned, we'll need the hash twice, so we
// compute it once and store it in capa
RSTRING(str)->as.heap.aux.capa = (long)str_do_hash(str);
}
#endif
RB_VM_LOCK_ENTER();
{
st_table *frozen_strings = rb_vm_fstring_table();
@ -531,7 +552,6 @@ static VALUE
setup_fake_str(struct RString *fake_str, const char *name, long len, int encidx)
{
fake_str->basic.flags = T_STRING|RSTRING_NOEMBED|STR_NOFREE|STR_FAKESTR;
/* SHARED to be allocated by the callback */
if (!name) {
RUBY_ASSERT_ALWAYS(len == 0);