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Merged
merged 9 commits into from
Oct 29, 2025
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<regex>: Process generic loops non-recursively #5798

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435b2a1
`<regex>`: Process generic loops non-recursively
muellerj2 Oct 22, 2025
6883ea4
fix test for x86
muellerj2 Oct 22, 2025
93bbd6e
Extract code.
StephanTLavavej Oct 24, 2025
90eee22
Fix citation.
StephanTLavavej Oct 24, 2025
abd7f61
All shall love raw string literals and despair.
StephanTLavavej Oct 24, 2025
4e49a7c
Avoid unnecessary escapes.
StephanTLavavej Oct 24, 2025
5b699ff
Adjust test data to be fictional.
StephanTLavavej Oct 24, 2025
235ec50
Add a positive test case.
StephanTLavavej Oct 24, 2025
69c7c17
Drop `std::`.
StephanTLavavej Oct 24, 2025
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210 changes: 135 additions & 75 deletions stl/inc/regex
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Original file line number Diff line number Diff line change
Expand Up @@ -1682,14 +1682,19 @@ enum class _Rx_unwind_ops {
_Do_nothing,
_Loop_simple_nongreedy,
_Loop_simple_greedy,
_Loop_nongreedy,
_Loop_greedy,
_Loop_restore_vals,
};

template <class _BidIt>
class _Rx_state_frame_t {
public:
_Rx_unwind_ops _Code;
int _Loop_idx_sav;
_Node_base* _Node;
_Tgt_state_t<_BidIt> _Match_state;
size_t _Loop_frame_idx_sav;
};

template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
Expand Down Expand Up @@ -1816,7 +1821,6 @@ private:
void _Decrease_stack_usage_count();
void _Increase_complexity_count();

bool _Do_rep(_Node_rep*, bool, int);
void _Prepare_rep(_Node_rep*);
bool _Find_first_inner_capture_group(_Node_base*, _Loop_vals_v2_t*);
_It _Do_class(_Node_base*, _It);
Expand Down Expand Up @@ -3372,7 +3376,7 @@ void _Builder2<_FwdIt, _Elem, _RxTraits>::_Tidy() noexcept { // free memory
template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
size_t _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Push_frame(_Rx_unwind_ops _Code, _Node_base* _Node) {
if (_Frames_count >= _Frames.size()) {
_Frames.push_back({_Code, _Node, _Tgt_state});
_Frames.push_back({_Code, 0, _Node, _Tgt_state, size_t{}});
} else {
auto& _Frame = _Frames[_Frames_count];
_Frame._Code = _Code;
Expand Down Expand Up @@ -3413,74 +3417,6 @@ void _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Increase_complexity_coun
}
}

template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Do_rep(_Node_rep* _Node, bool _Greedy, int _Init_idx) {
// apply repetition
bool _Matched0 = false;
_Loop_vals_v2_t* _Psav = &_Loop_vals[_Node->_Loop_number];
const int _Loop_idx_sav = _Psav->_Loop_idx;
const size_t _Loop_frame_idx_sav = _Psav->_Loop_frame_idx;
const size_t _Frame_idx = _Push_frame();
const bool _Progress = _Init_idx == 0 || _Frames[_Loop_frame_idx_sav]._Match_state._Cur != _Tgt_state._Cur;

if (_Init_idx < _Node->_Min) { // try another required match
_Psav->_Loop_frame_idx = _Frame_idx;
_Psav->_Loop_idx = _Progress ? _Init_idx + 1 : _Node->_Min; // try only one more match after an empty match
_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Psav->_Group_first),
_Tgt_state._Grp_valid.end(), false);
_Matched0 = _Match_pat(_Node->_Next);
} else if (_Init_idx == _Node->_Min || _Progress) {
if (0 <= _Node->_Max && _Node->_Max <= _Init_idx) {
_Matched0 = _Match_pat(_Node->_End_rep->_Next); // reps done, try tail
} else if (_Longest) { // longest, try any number of repetitions

// match with no further repetition
_Matched0 = _Match_pat(_Node->_End_rep->_Next);

// try to match with one more repetition
_Tgt_state = _Frames[_Frame_idx]._Match_state;
_Psav->_Loop_idx = _Init_idx + 1;
_Psav->_Loop_frame_idx = _Frame_idx;
if (_Match_pat(_Node->_Next)) { // always call _Match_pat, even when _Matched0 is already true
_Matched0 = true;
}
} else if (!_Greedy) { // not greedy, favor minimum number of reps
_Matched0 = _Match_pat(_Node->_End_rep->_Next);
if (!_Matched0) { // tail failed, try another rep
_Tgt_state = _Frames[_Frame_idx]._Match_state;
_Psav->_Loop_idx = _Init_idx + 1;
_Psav->_Loop_frame_idx = _Frame_idx;
_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Psav->_Group_first),
_Tgt_state._Grp_valid.end(), false);
_Matched0 = _Match_pat(_Node->_Next);
}
} else { // greedy, favor maximum number of reps,
// so try another rep
_Psav->_Loop_idx = _Init_idx + 1;
_Psav->_Loop_frame_idx = _Frame_idx;
_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Psav->_Group_first),
_Tgt_state._Grp_valid.end(), false);
_Matched0 = _Match_pat(_Node->_Next);

if (!_Matched0) { // rep failed, try tail
_Psav->_Loop_idx = _Loop_idx_sav;
_Psav->_Loop_frame_idx = _Loop_frame_idx_sav;
_Tgt_state = _Frames[_Frame_idx]._Match_state;
_Matched0 = _Match_pat(_Node->_End_rep->_Next);
}
}
} else if (_Init_idx == 1 && (_Sflags & regex_constants::_Any_posix)) {
// POSIX allows an empty repetition if the subexpression is matched only once,
// so try tail
_Matched0 = _Match_pat(_Node->_End_rep->_Next);
}

_Psav->_Loop_idx = _Loop_idx_sav;
_Psav->_Loop_frame_idx = _Loop_frame_idx_sav;
_Pop_frame(_Frame_idx);
return _Matched0;
}

template <class _BidIt, class _Elem, class _RxTraits, class _It, class _Alloc>
void _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Prepare_rep(_Node_rep* _Node) {
_Loop_vals_v2_t* _Psav = &_Loop_vals[_Node->_Loop_number];
Expand Down Expand Up @@ -4055,9 +3991,9 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
auto _Node = static_cast<_Node_rep*>(_Nx);
_Prepare_rep(_Node);
bool _Greedy = (_Node->_Flags & _Fl_greedy) != 0;
auto& _Sav = _Loop_vals[_Node->_Loop_number];

if (_Node->_Simple_loop == 1) {
auto& _Sav = _Loop_vals[_Node->_Loop_number];
_Sav._Loop_frame_idx = _Push_frame(_Rx_unwind_ops::_Do_nothing);
_Increase_complexity_count();
if (_Node->_Min > 0 || (_Greedy && !_Longest && _Node->_Max != 0)) { // try a rep first
Expand All @@ -4078,8 +4014,33 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
}
}
} else {
_Failed = !_Do_rep(_Node, _Greedy, 0);
_Next = nullptr;
if (_Node->_Min > 0 || (_Greedy && !_Longest && _Node->_Max != 0)) { // try a rep first
// set up stack unwinding for greedy matching or loop val restoration
auto _Frame_idx = _Push_frame(
_Node->_Min == 0 ? _Rx_unwind_ops::_Loop_greedy : _Rx_unwind_ops::_Loop_restore_vals,
_Node);
auto& _Frame = _Frames[_Frame_idx];
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_idx = 1;
_Sav._Loop_frame_idx = _Frame_idx;
_Increase_stack_usage_count();
// _Next is already assigned correctly for matching a rep
} else { // try tail first
_Next = _Node->_End_rep->_Next;
// set up stack unwinding for non-greedy matching if at least one rep is allowed
if (_Node->_Max != 0) {
auto _Frame_idx = _Push_frame(_Rx_unwind_ops::_Loop_nongreedy, _Node);
auto& _Frame = _Frames[_Frame_idx];
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_idx = 0;
_Sav._Loop_frame_idx = _Frame_idx;
_Increase_stack_usage_count();
} else {
_Increase_complexity_count();
}
}
}
}

Expand Down Expand Up @@ -4128,8 +4089,62 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
_Increase_complexity_count();
}
} else {
_Failed = !_Do_rep(_Nr, _Greedy, _Sav._Loop_idx);
_Next = nullptr;
const bool _Progress = _Frames[_Sav._Loop_frame_idx]._Match_state._Cur != _Tgt_state._Cur;
if (_Sav._Loop_idx < _Nr->_Min) { // try another required match
auto _Frame_idx = _Push_frame(_Rx_unwind_ops::_Loop_restore_vals, _Nr);
auto& _Frame = _Frames[_Frame_idx];
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_frame_idx = _Frame_idx;
if (_Progress) {
++_Sav._Loop_idx;
} else { // try only one more match after an empty match
_Sav._Loop_idx = _Nr->_Min;
}
_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Sav._Group_first),
_Tgt_state._Grp_valid.end(), false);
_Next = _Nr->_Next;
_Increase_stack_usage_count();
} else if (!_Progress) { // latest rep match empty
// An empty match is allowed if it is needed to reach the minimum number of reps.
// Moreover, POSIX allows an empty repetition if the subexpression is matched only once.
// So try tail in either case, else fail.
if (_Sav._Loop_idx != _Nr->_Min
&& !((_Sflags & regex_constants::_Any_posix) && _Sav._Loop_idx == 1)) {
_Failed = true;
} else {
_Increase_complexity_count();
}
// _Next is already assigned correctly for matching tail
} else if (_Greedy && !_Longest && _Sav._Loop_idx != _Nr->_Max) { // one more rep to try next
// set up stack unwinding for greedy matching
auto _Frame_idx = _Push_frame(_Rx_unwind_ops::_Loop_greedy, _Nr);
auto& _Frame = _Frames[_Frame_idx];
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_frame_idx = _Frame_idx;
if (_Sav._Loop_idx < INT_MAX) {
++_Sav._Loop_idx;
}

_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Sav._Group_first),
_Tgt_state._Grp_valid.end(), false);
_Next = _Nr->_Next;
_Increase_stack_usage_count();
} else { // non-greedy matching or greedy matching with maximum reached
// set up stack unwinding for non-greedy matching if one more rep is allowed
if (_Sav._Loop_idx != _Nr->_Max) {
auto _Frame_idx = _Push_frame(_Rx_unwind_ops::_Loop_nongreedy, _Nr);
auto& _Frame = _Frames[_Frame_idx];
_Frame._Loop_idx_sav = _Sav._Loop_idx;
_Frame._Loop_frame_idx_sav = _Sav._Loop_frame_idx;
_Sav._Loop_frame_idx = _Frame_idx;
_Increase_stack_usage_count();
} else {
_Increase_complexity_count();
}
// _Next is already assigned correctly for matching tail
}
}
break;
}
Expand Down Expand Up @@ -4249,6 +4264,51 @@ bool _Matcher3<_BidIt, _Elem, _RxTraits, _It, _Alloc>::_Match_pat(_Node_base* _N
}
break;

case _Rx_unwind_ops::_Loop_greedy:
// try tail if matching one more rep failed
if (_Failed) {
auto _Node = static_cast<_Node_rep*>(_Frame._Node);

_Increase_complexity_count();
_Nx = _Node->_End_rep->_Next;
_Tgt_state = _Frame._Match_state;
_Failed = false;
}
_FALLTHROUGH;

case _Rx_unwind_ops::_Loop_restore_vals:
{ // restore loop vals after processing of a rep is completed
auto _Node = static_cast<_Node_rep*>(_Frame._Node);
auto& _Sav = _Loop_vals[_Node->_Loop_number];

_Sav._Loop_idx = _Frame._Loop_idx_sav;
_Sav._Loop_frame_idx = _Frame._Loop_frame_idx_sav;

_Decrease_stack_usage_count();
}
break;

case _Rx_unwind_ops::_Loop_nongreedy:
// try another rep if matching tail failed or longest mode
if (_Failed || _Longest) {
auto _Node = static_cast<_Node_rep*>(_Frame._Node);
auto& _Sav = _Loop_vals[_Node->_Loop_number];

_Increase_complexity_count();
_Nx = _Node->_Next;
_Tgt_state = _Frame._Match_state;
_STD fill(_Tgt_state._Grp_valid.begin() + static_cast<ptrdiff_t>(_Sav._Group_first),
_Tgt_state._Grp_valid.end(), false);
_Failed = false;
if (_Sav._Loop_idx < INT_MAX) { // avoid overflowing _Loop_idx
++_Sav._Loop_idx;
}

_Frame._Code = _Rx_unwind_ops::_Loop_restore_vals;
++_Frames_count;
}
break;

default:
#if _ITERATOR_DEBUG_LEVEL != 0
_STL_REPORT_ERROR("internal stack of regex matcher corrupted");
Expand Down
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