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Speed up string compares in string interning.

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This commit is contained in:
Mike Pall 2010-07-21 23:55:05 +02:00
parent 420124372b
commit c5feda2d53
2 changed files with 51 additions and 6 deletions
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10
src/lj.supp
View File

@ -4,3 +4,13 @@
Memcheck:Addr4
fun:lj_str_cmp
}
{
Optimized string compare
Memcheck:Addr4
fun:lj_str_new
}
{
Optimized string compare
Memcheck:Cond
fun:lj_str_new
}

47
src/lj_str.c
View File

@ -43,6 +43,27 @@ int32_t LJ_FASTCALL lj_str_cmp(GCstr *a, GCstr *b)
return (int32_t)(a->len - b->len);
}
/* Fast string data comparison. Caveat: unaligned access to 1st string! */
static LJ_AINLINE int str_fastcmp(const char *a, const char *b, MSize len)
{
MSize i = 0;
lua_assert(len > 0);
lua_assert((((uintptr_t)a + len) & (LJ_PAGESIZE-1)) <= LJ_PAGESIZE-4);
do { /* Note: innocuous access up to end of string + 3. */
uint32_t v = *(const uint32_t *)(a+i) ^ *(const uint32_t *)(b+i);
if (v) {
i -= len;
#if LJ_ARCH_ENDIAN == LUAJIT_LE
return (int32_t)i >= -3 ? (v << (32+(i<<3))) : 1;
#else
return (int32_t)i >= -3 ? (v >> (32+(i<<3))) : 1;
#endif
}
i += 4;
} while (i < len);
return 0;
}
/* Resize the string hash table (grow and shrink). */
void lj_str_resize(lua_State *L, MSize newmask)
{
@ -99,12 +120,26 @@ GCstr *lj_str_new(lua_State *L, const char *str, size_t lenx)
b ^= a; b -= lj_rol(a, 25);
h ^= b; h -= lj_rol(b, 16);
/* Check if the string has already been interned. */
for (o = gcref(g->strhash[h & g->strmask]); o != NULL; o = gcnext(o)) {
GCstr *tso = gco2str(o);
if (tso->len == len && (memcmp(str, strdata(tso), len) == 0)) {
/* Resurrect if dead. Can only happen with fixstring() (keywords). */
if (isdead(g, o)) flipwhite(o);
return tso; /* Return existing string. */
o = gcref(g->strhash[h & g->strmask]);
if (LJ_LIKELY((((uintptr_t)str + len) & (LJ_PAGESIZE-1)) <= LJ_PAGESIZE-4)) {
while (o != NULL) {
GCstr *sx = gco2str(o);
if (sx->len == len && str_fastcmp(str, strdata(sx), len) == 0) {
/* Resurrect if dead. Can only happen with fixstring() (keywords). */
if (isdead(g, o)) flipwhite(o);
return sx; /* Return existing string. */
}
o = gcnext(o);
}
} else { /* Slow path: end of string is too close to a page boundary. */
while (o != NULL) {
GCstr *sx = gco2str(o);
if (sx->len == len && memcmp(str, strdata(sx), len) == 0) {
/* Resurrect if dead. Can only happen with fixstring() (keywords). */
if (isdead(g, o)) flipwhite(o);
return sx; /* Return existing string. */
}
o = gcnext(o);
}
}
/* Nope, create a new string. */