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<regex>: Avoid allocating during matching when regex defines no captures #5518

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Merged
merged 1 commit into from
May 22, 2025
Merged

<regex>: Avoid allocating during matching when regex defines no captures #5518

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1 change: 1 addition & 0 deletions benchmarks/src/regex_search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ void bm_lorem_search(benchmark::State& state, const char* pattern) {
}

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);

Expand Down
40 changes: 27 additions & 13 deletions stl/inc/regex
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Original file line number Diff line number Diff line change
Expand Up @@ -1695,9 +1695,10 @@ public:
}

_Tgt_state._Cur = _Begin;
_Tgt_state._Grp_valid.resize(_Ncap);
_Tgt_state._Grps.resize(_Ncap);
_Cap = static_cast<bool>(_Matches);
if (_Ncap > 1U) {
_Tgt_state._Grp_valid.resize(_Ncap);
_Tgt_state._Grps.resize(_Ncap);
}
_Full = _Full_match;
_Max_complexity_count = _REGEX_MAX_COMPLEXITY_COUNT;
_Max_stack_count = _REGEX_MAX_STACK_COUNT;
Expand All @@ -1711,7 +1712,13 @@ public:
if (_Matches) { // copy results to _Matches
_Matches->_Resize(_Ncap);
const auto& _Result = _Longest ? _Res : _Tgt_state;
for (unsigned int _Idx = 0; _Idx < _Ncap; ++_Idx) { // copy submatch _Idx

auto& _Submatch0 = _Matches->_At(0U);
_Submatch0.matched = true;
_Submatch0.first = _Begin;
_Submatch0.second = _Result._Cur;

for (unsigned int _Idx = 1U; _Idx < _Ncap; ++_Idx) { // copy submatch _Idx
if (_Result._Grp_valid[_Idx]) { // copy successful match
_Matches->_At(_Idx).matched = true;
_Matches->_At(_Idx).first = _Result._Grps[_Idx]._Begin;
Expand Down Expand Up @@ -1763,7 +1770,6 @@ private:
regex_constants::syntax_option_type _Sflags;
regex_constants::match_flag_type _Mflags;
bool _Matched = false;
bool _Cap;
unsigned int _Ncap;
bool _Longest;
const _RxTraits& _Traits;
Expand Down Expand Up @@ -3499,10 +3505,10 @@ bool _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Do_rep_first(_Node_rep*

// Determine first capture group in repetition for later capture group reset, if not done so previously.
// No capture group reset is performed for POSIX regexes,
// so we prevent any reset by setting the first capture group to the number of capture groups _Ncap.
if (_Psav->_Group_first == 0) {
// so we prevent any reset by setting the first capture group to the size of the capture group vector.
if (_Psav->_Group_first == 0U) {
if ((_Sflags & regex_constants::_Any_posix) || !_Find_first_inner_capture_group(_Node->_Next, _Psav)) {
_Psav->_Group_first = _Ncap;
_Psav->_Group_first = static_cast<unsigned int>(_Tgt_state._Grp_valid.size());
}
}

Expand Down Expand Up @@ -3573,7 +3579,7 @@ bool _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Find_first_inner_capture
_Found_group = true;
_Nx = nullptr;
} else {
_Inner_loop_state->_Group_first = _Ncap;
_Inner_loop_state->_Group_first = static_cast<unsigned int>(_Tgt_state._Grp_valid.size());
_Nx = _Inner_rep->_End_rep;
}
break;
Expand Down Expand Up @@ -3781,7 +3787,13 @@ _It _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Do_class(_Node_base* _Nx,
template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
bool _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Better_match() {
// check for better match under leftmost-longest rule
for (unsigned int _Ix = 0; _Ix < _Ncap; ++_Ix) { // check each capture group

// a longer match is better than a shorter one
if (_Res._Cur != _Tgt_state._Cur) {
return _STD distance(_Begin, _Res._Cur) < _STD distance(_Begin, _Tgt_state._Cur);
}

for (unsigned int _Ix = 1U; _Ix < _Ncap; ++_Ix) { // check each capture group
// any match (even an empty one) is better than no match at all
if (_Res._Grp_valid[_Ix] != _Tgt_state._Grp_valid[_Ix]) {
return _Tgt_state._Grp_valid[_Ix];
Expand Down Expand Up @@ -3939,16 +3951,18 @@ bool _Matcher2<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N

case _N_capture:
{ // record current position
_Node_capture* _Node = static_cast<_Node_capture*>(_Nx);
_Tgt_state._Grps[_Node->_Idx]._Begin = _Tgt_state._Cur;
_Node_capture* _Node = static_cast<_Node_capture*>(_Nx);
if (_Node->_Idx != 0U) {
_Tgt_state._Grps[_Node->_Idx]._Begin = _Tgt_state._Cur;
}
break;
}

case _N_end_capture:
{ // record successful capture
_Node_end_group* _Node = static_cast<_Node_end_group*>(_Nx);
_Node_capture* _Node0 = static_cast<_Node_capture*>(_Node->_Back);
if (_Cap || _Node0->_Idx != 0) { // update capture data
if (_Node0->_Idx != 0U) { // update capture data
_Tgt_state._Grp_valid[_Node0->_Idx] = true;
_Tgt_state._Grps[_Node0->_Idx]._End = _Tgt_state._Cur;
}
Expand Down