Aegisub/vendor/luajit/0001-lj_str.c-Remove-special-case-string-interning-fastpa.patch
Luke Gorrie 45cd713ef9 lj_str.c: Remove special-case string interning fastpath
lj_str_new() had a separate fast-path and slow-path. This was bad
because (a) the fast-path was complex and (b) the fast-path was
actually slower than the slow-path in practice and (c) in practice it
could cause confusing performance problems depending on the memory
alignment of any often-reused string buffers in a program.

This change specifically makes the 'life' benchmark faster and more
robust to memory layout.
2019-11-02 00:23:50 -04:00

83 lines
3 KiB
Diff

From fcf86b84772735a3195af034d0bc7ed0f4106337 Mon Sep 17 00:00:00 2001
From: Luke Gorrie <luke@snabb.co>
Date: Wed, 3 Jan 2018 13:04:56 +0000
Subject: [PATCH] lj_str.c: Remove special-case string interning fastpath
lj_str_new() had a separate fast-path and slow-path. This was bad
because (a) the fast-path was complex and (b) the fast-path was
actually slower than the slow-path in practice and (c) in practice it
could cause confusing performance problems depending on the memory
alignment of any often-reused string buffers in a program.
This change specifically makes the 'life' benchmark faster and more
robust to memory layout.
---
src/lj_str.c | 47 +++++++----------------------------------------
1 file changed, 7 insertions(+), 40 deletions(-)
diff --git a/src/lj_str.c b/src/lj_str.c
index b32d1398..d8f314ae 100644
--- a/src/lj_str.c
+++ b/src/lj_str.c
@@ -37,27 +37,6 @@ int32_t 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-1) & (LJ_PAGESIZE-1)) <= LJ_PAGESIZE-4);
- do { /* Note: innocuous access up to end of string + 3. */
- uint32_t v = lj_getu32(a+i) ^ *(const uint32_t *)(b+i);
- if (v) {
- i -= len;
-#if LJ_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;
-}
-
/* Find fixed string p inside string s. */
const char *lj_str_find(const char *s, const char *p, MSize slen, MSize plen)
{
@@ -149,26 +128,14 @@ GCstr *lj_str_new(lua_State *L, const char *str, size_t lenx)
h ^= b; h -= lj_rol(b, 16);
/* Check if the string has already been interned. */
o = gcref(g->strhash[h & g->strmask]);
- if (LJ_LIKELY((((uintptr_t)str+len-1) & (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);
+ 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. */
s = lj_mem_newt(L, sizeof(GCstr)+len+1, GCstr);