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AHOCORASICK - Reduce heap allocation overhead

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A `U8*` structure is used to track character positions during Aho-Corasick
string searching. This used to always be allocated from the heap, and
wrapped in a mortal SV to avoid leakage. However, that incurs overhead.

Following this commit:
* A stack buffer is used if `maxlen` is small enough.
* Otherwise, the heap allocation is saved directly to the savestack
for freeing during stack unwinding.
* Since a mortal SV is no longer used, there is no need to `SAVETMPS`
and `FREETMPS` at scope entry/exit.
This commit is contained in:
Richard Leach 2025-10-18 23:39:31 +00:00
parent a2ff23c0fd
commit 1a871ce3a5
1 changed files with 30 additions and 17 deletions
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47
regexec.c
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@ -3258,29 +3258,40 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
const char *real_start = s;
#endif
STRLEN maxlen = trie->maxlen;
SV *sv_points;
U8 **points; /* map of where we were in the input string
when reading a given char. For ASCII this
is unnecessary overhead as the relationship
is always 1:1, but for Unicode, especially
case folded Unicode this is not true. */
/* For a shorter maxlen, points are stored in a stack buffer. */
/* The choice of STACK_POINTS_MAX here is rather arbitrary.
* When building perl and running test_harness, maxlen rarely
* goes above 8, but presumbaly there are good business cases
* where a somewhat larger value is common. */
enum { STACK_POINTS_MAX = 32 };
U8 *points_stack[STACK_POINTS_MAX];
/* Otherwise, a more costly heap allocation is used. */
bool used_heap = false;
U8 foldbuf[ UTF8_MAXBYTES_CASE + 1 ];
U8 *bitmap = NULL;
U8 **points_heap = NULL;
DECLARE_AND_GET_RE_DEBUG_FLAGS;
/* We can't just allocate points here. We need to wrap it in
* an SV so it gets freed properly if there is a croak while
* running the match */
ENTER;
SAVETMPS;
sv_points = newSV(maxlen * sizeof(U8 *));
SvCUR_set(sv_points,
maxlen * sizeof(U8 *));
SvPOK_on(sv_points);
sv_2mortal(sv_points);
points = (U8**)SvPV_nolen(sv_points );
if (maxlen <= STACK_POINTS_MAX) {
points = points_stack;
} else {
used_heap = true;
/* In case of a die event, the allocation will be freed
as the savestack is unwound. */
ENTER;
Newx(points_heap, maxlen, U8*);
SAVEFREEPV(points_heap);
points = points_heap;
}
if ( trie_type != trie_utf8_fold
&& (trie->bitmap || OP(c)==AHOCORASICKC) )
{
@ -3464,8 +3475,9 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
);
});
if (reginfo->intuit || regtry(reginfo, &s)) {
FREETMPS;
LEAVE;
if (used_heap) {
LEAVE;
}
goto got_it;
}
if (s < reginfo->strend) {
@ -3482,8 +3494,9 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
break;
}
}
FREETMPS;
LEAVE;
if (used_heap) {
LEAVE;
}
}
break;