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<regex>: Speed up searches for regexes that start with assertions #5576

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Merged
StephanTLavavej merged 2 commits into from
Jun 14, 2025
Merged

<regex>: Speed up searches for regexes that start with assertions #5576

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8b321d2
`<regex>`: Speed up searches for regexes that start with assertions
muellerj2 Jun 7, 2025
adc8323
Merge branch 'main' into regex-speedup-assertion-searches
StephanTLavavej Jun 14, 2025
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5 changes: 5 additions & 0 deletions benchmarks/src/regex_search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -36,5 +36,10 @@ BENCHMARK_CAPTURE(bm_lorem_search, "bibe", "bibe")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, "(bibe)", "(bibe)")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, "(bibe)+", "(bibe)+")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, "(?:bibe)+", "(?:bibe)+")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, R"(\bbibe)", R"(\bbibe)")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, R"(\Bibe)", R"(\Bibe)")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, R"((?=....)bibe)", R"((?=....)bibe)")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, R"((?=bibe)....)", R"((?=bibe)....)")->Arg(2)->Arg(3)->Arg(4);
BENCHMARK_CAPTURE(bm_lorem_search, R"((?!lorem)bibe)", R"((?!lorem)bibe)")->Arg(2)->Arg(3)->Arg(4);

BENCHMARK_MAIN();
51 changes: 45 additions & 6 deletions stl/inc/regex
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Expand Up @@ -1781,7 +1781,7 @@ public:
return true;
}

_BidIt _Skip(_BidIt, _BidIt, _Node_base* = nullptr);
_BidIt _Skip(_BidIt, _BidIt, _Node_base* = nullptr, unsigned int _Recursion_depth = 0U);

private:
_Tgt_state_t<_It> _Tgt_state;
Expand Down Expand Up @@ -4107,12 +4107,14 @@ bool _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
}

template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
_BidIt _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Skip(_BidIt _First_arg, _BidIt _Last, _Node_base* _Node_arg) {
_BidIt _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Skip(
_BidIt _First_arg, _BidIt _Last, _Node_base* _Node_arg, unsigned int _Recursion_depth) {
// skip until possible match
// assumes --_First_arg is valid
static constexpr char _Line_terminators_char[] = {static_cast<char>(_Meta_cr), static_cast<char>(_Meta_nl)};
static constexpr wchar_t _Line_terminators_wchar_t[] = {static_cast<wchar_t>(_Meta_cr),
static_cast<wchar_t>(_Meta_nl), static_cast<wchar_t>(_Meta_ls), static_cast<wchar_t>(_Meta_ps)};
constexpr unsigned int _Max_recursion_depth = 50U;
_Node_base* _Nx = _Node_arg ? _Node_arg : _Rep;

while (_First_arg != _Last && _Nx) { // check current node
Expand Down Expand Up @@ -4227,17 +4229,54 @@ _BidIt _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Skip(_BidIt _First_arg
break;
}

case _N_assert:
{
if (_Recursion_depth >= _Max_recursion_depth) {
return _First_arg;
}

_Node_assert* _Node = static_cast<_Node_assert*>(_Nx);
_First_arg = _Skip(_First_arg, _Last, _Node->_Child);
_BidIt _Next;
for (;;) {
_Next = _Skip(_First_arg, _Last, _Node->_Next, _Recursion_depth + 1U);
if (_Next == _First_arg) {
return _First_arg;
}

_First_arg = _Skip(_Next, _Last, _Node->_Child, _Recursion_depth + 1U);
if (_Next == _First_arg) {
return _First_arg;
}
}
}

case _N_neg_assert:
// we skip the negated assertion body and continue examining the rest of the regex
break;

case _N_wbound:
{
bool _Negated = (_Nx->_Flags & _Fl_negate) != 0;
bool _Prev_word = _STD _Is_word(*_STD _Prev_iter(_First_arg));
for (; _First_arg != _Last; ++_First_arg) {
bool _Next_word = _STD _Is_word(*_First_arg);
if (_Negated == (_Next_word == _Prev_word)) {
break;
}
_Prev_word = _Next_word;
}
return _First_arg;
}

case _N_begin:
case _N_endif:
break;

case _N_end:
case _N_none:
case _N_wbound:
case _N_dot:
case _N_assert:
case _N_neg_assert:
case _N_back:
case _N_endif:
case _N_end_rep:
default:
return _First_arg;
Expand Down
16 changes: 14 additions & 2 deletions tests/std/tests/VSO_0000000_regex_use/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -234,8 +234,8 @@ void test_VSO_167760_nested_quantifiers_should_not_infinite_loop() {
void test_DDB_153116_replacements() {
g_regexTester.should_replace_to("abc def def ghi", "^", "X", format_default, "Xabc def def ghi");
g_regexTester.should_replace_to("abc def def ghi", "$", "X", format_default, "abc def def ghiX");
g_regexTester.should_replace_to("abc def def ghi", "\\b", "X", format_default, "XabcX XdefX XdefX XghiX");
g_regexTester.should_replace_to("abc def def ghi", "\\B", "X", format_default, "aXbXc dXeXf dXeXf gXhXi");
g_regexTester.should_replace_to("abc def def ghi", "\\b", "X", format_default, "XabcX XdefX XdefX XghiX");
g_regexTester.should_replace_to("abc def def ghi", "\\B", "X", format_default, "aXbXc X dXeXf dXeXf X gXhXi");
g_regexTester.should_replace_to("abc def def ghi", "(?=ef)", "X", format_default, "abc dXef dXef ghi");
g_regexTester.should_replace_to("abc def def ghi", "(?!ef)", "X", format_default, "XaXbXcX XdeXfX XdeXfX XgXhXiX");
}
Expand Down Expand Up @@ -2092,6 +2092,17 @@ void test_gh_5509() {
}
}

void test_gh_5576() {
// GH-5576 sped up searches for regexes that start with assertions
// by extending the skip heuristic in the matcher.
// We test here that the skip heuristic is correct
// for positive and negative lookahead assertions.
g_regexTester.should_replace_to("AbGweEfFllLLlffflElF", "(?=[[:lower:]][[:upper:]])[fFlL]{2}", R"(X$&)",
match_default, "AbGweEXfFlXlLLlffflEXlF");
g_regexTester.should_replace_to("AbGweEfFllLLlffflElF", "(?![[:upper:]]|[[:lower:]]{2})[fFlL]{2}", R"(X$&)",
match_default, "AbGweEXfFlXlLLlffflEXlF");
}

int main() {
test_dev10_449367_case_insensitivity_should_work();
test_dev11_462743_regex_collate_should_not_disable_regex_icase();
Expand Down Expand Up @@ -2141,6 +2152,7 @@ int main() {
test_gh_5377();
test_gh_5490();
test_gh_5509();
test_gh_5576();

return g_regexTester.result();
}