https://gcc.gnu.org/g:dc65d88cdf15f3538fdcfd1d174c845474989533
commit r17-4552-gdc65d88cdf15f3538fdcfd1d174c845474989533 Author: Tamar Christina <[email protected]> Date: Tue Sep 22 07:19:56 2026 +0100 libstdc++: Continue with regex DFS traversals without next frames [PR126274] The change in r16-7193-g158ad5f96954da5fa24d5c2a91ae92417fb62e20 changed the recursive implementation with an iterative one using an explicit heap. However one benefit of the previous implementation is that the frame did not have to be saved and popped when the match is supposed to continue. This means that on hot paths we now have additional memory accesses and need additional instructions to calculate the memref addresses. For DFS matching this is clearly suboptimal since when _M_rep_once_more then we push and pop the same state but there is enough other acceses in between the push and pop that we get a lot of cache misses. This makes all the private _m_handle_* methods return a _StateIdT which allows the caller to deal with the value, so that for DFS we can avoid pushing the frame if needed. For DFS we try to consume the state immediately until we're told to stop. For this to work the methods have to me marked always inline, because a key part of the optimization is to keep the values in registers rather than passing through stack and the function call overheads and AAPCS requirements would negate the benefits. The __dfs_mode changes are because the constexpr patch still gave a big boost so it prepares to apply it. There is still a regression until the end of the series and each patch will chip away at it. Also note that with none of these changes do I see an increase heap or stack usage that the original fix fixed. RSS stays about the same. PS. thanks for the link to the algorithm in the source, it was useful to understand how the machinery works! Benchmark improvements vs GCC 16: at -O2: email: +36.1% URI: +36.5% IPv4 +33.0% at -O3: email: +45.5%, URI: +44.9% IPv4: +43.0% On Neoverse-V1 libstdc++-v3/ChangeLog: PR libstdc++/126274 * include/bits/regex_executor.h (_Executor): Reserve frame space. (_M_rep_once_more, _M_handle_repeat, _M_handle_subexpr_begin, _M_handle_subexpr_end, _M_handle_line_begin_assertion, _M_handle_line_end_assertion, _M_handle_word_boundary, _M_handle_subexpr_lookahead, _M_handle_match, _M_handle_backref, _M_node): return StateIdT. (_M_visited): Mark inline. * include/bits/regex_executor.tcc (_M_rep_once_more, _M_handle_repeat, _M_handle_subexpr_begin, _M_handle_subexpr_end, _M_handle_line_begin_assertion, _M_handle_line_end_assertion, _M_handle_word_boundary, _M_handle_subexpr_lookahead, _M_handle_match, _M_handle_backref): Return state, mark always inline. (_M_node): Return StateIdT and also decide what to do with the value after return. (_M_dfs): Traverse states iteratively for _S_fopcode_next, _S_fopcode_fallback_next, _S_fopcode_fallback_rep_once_more and _S_fopcode_rep_once_more. * include/bits/regex.h (class _Executor): Move to V2 ABI. Diff: --- libstdc++-v3/include/bits/regex.h | 2 + libstdc++-v3/include/bits/regex_executor.h | 30 +++-- libstdc++-v3/include/bits/regex_executor.tcc | 183 ++++++++++++++++++--------- 3 files changed, 139 insertions(+), 76 deletions(-) diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h index 0e815ca086eb..dce420251db0 100644 --- a/libstdc++-v3/include/bits/regex.h +++ b/libstdc++-v3/include/bits/regex.h @@ -61,8 +61,10 @@ namespace __detail _RegexExecutorPolicy __policy, bool __match_mode); +_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2) template<typename, typename, typename> class _Executor; +_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2) template<typename _Tp> struct __is_contiguous_iter : false_type { }; diff --git a/libstdc++-v3/include/bits/regex_executor.h b/libstdc++-v3/include/bits/regex_executor.h index 797ad702784b..eccf12c5a087 100644 --- a/libstdc++-v3/include/bits/regex_executor.h +++ b/libstdc++-v3/include/bits/regex_executor.h @@ -44,6 +44,7 @@ namespace __detail template<typename _BiIter, bool _Trivial = is_trivially_copyable<_BiIter>::value> struct _ExecutorFrame; +_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2) /** * @brief Takes a regex and an input string and does the matching. * @@ -113,43 +114,43 @@ namespace __detail _M_search(); private: - void + _StateIdT _M_rep_once_more(_Match_mode __match_mode, _StateIdT); - void + _StateIdT _M_handle_repeat(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_subexpr_begin(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_subexpr_end(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_line_begin_assertion(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_line_end_assertion(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_word_boundary(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_subexpr_lookahead(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_match(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_backref(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_accept(_Match_mode, _StateIdT); - void + _StateIdT _M_handle_alternative(_Match_mode, _StateIdT); - void + _StateIdT _M_node(_Match_mode, _StateIdT); void @@ -247,7 +248,7 @@ namespace __detail return (_M_re._M_automaton->_M_options() & __m) == __m; } - bool + inline bool _M_visited(_StateIdT __i) { if (_M_visited_states) @@ -283,6 +284,7 @@ namespace __detail // Do we have a solution so far? bool _M_has_sol; }; +_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2) ///@} regex-detail } // namespace __detail diff --git a/libstdc++-v3/include/bits/regex_executor.tcc b/libstdc++-v3/include/bits/regex_executor.tcc index 167a7a345300..9361c27d4c5b 100644 --- a/libstdc++-v3/include/bits/regex_executor.tcc +++ b/libstdc++-v3/include/bits/regex_executor.tcc @@ -250,8 +250,14 @@ namespace __detail // infinite loop by refusing to continue when it's already been // visited more than twice. It's `twice` instead of `once` because // we need to spare one more time for potential group capture. + // + // If the node cannot be re-entered anymore from the current state then return + // _S_invalid_state_id otherwise return the current state without going + // through a vector, allowing the caller to decide what to do with the state + // This is beneficial for DFS since DFS can continue with the next state + // immediately template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: + _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_rep_once_more(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; @@ -263,7 +269,7 @@ namespace __detail _M_frames.back()._M_count = __rep_count.second; __rep_count.first = _M_current; __rep_count.second = 1; - _M_frames.emplace_back(_S_fopcode_next, __state._M_alt); + return __state._M_alt; } else { @@ -271,9 +277,10 @@ namespace __detail { __rep_count.second++; _M_frames.emplace_back(_S_fopcode_decrement_rep_count, __i); - _M_frames.emplace_back(_S_fopcode_next, __state._M_alt); + return __state._M_alt; } } + return _S_invalid_state_id; } // _M_alt branch is "match once more", while _M_next is "get me out @@ -281,8 +288,11 @@ namespace __detail // mean the same thing, and we need to choose the correct order under // given greedy mode. template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: - _M_handle_repeat(_Match_mode, _StateIdT __i) +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: + _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; // Greedy. @@ -294,7 +304,7 @@ namespace __detail _M_current); else _M_frames.emplace_back(_S_fopcode_next, __state._M_next); - _M_frames.emplace_back(_S_fopcode_rep_once_more, __i); + return _M_rep_once_more(__match_mode, __i); } else // Non-greedy mode { @@ -303,7 +313,7 @@ namespace __detail // vice-versa. _M_frames.emplace_back(_S_fopcode_fallback_rep_once_more, __i, _M_current); - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } else { @@ -316,97 +326,122 @@ namespace __detail // accepted state *must* be better than a solution that // matches a non-greedy quantifier one more time. _M_frames.emplace_back(_S_fopcode_fallback_rep_once_more, __i); - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } } } + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_subexpr_begin(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; auto& __res = _M_cur_results[__state._M_subexpr]; - _M_frames.emplace_back(_S_fopcode_restore_cur_results, - static_cast<_StateIdT>(__state._M_subexpr), - __res.first); + if (_M_nfa._M_has_backref + || __state._M_subexpr != 0 + || _M_search_mode != _Search_mode::_DFS) + _M_frames.emplace_back(_S_fopcode_restore_cur_results, + static_cast<_StateIdT>(__state._M_subexpr), + __res.first); __res.first = _M_current; - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_subexpr_end(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; auto& __res = _M_cur_results[__state._M_subexpr]; - _M_frames.emplace_back(_S_fopcode_restore_cur_results, - static_cast<_StateIdT>(__state._M_subexpr), - __res.second); - _M_frames.back()._M_subexpr_end = true; - _M_frames.back()._M_matched = __res.matched; + if (_M_nfa._M_has_backref + || __state._M_subexpr != 0 + || _M_search_mode != _Search_mode::_DFS) + { + _M_frames.emplace_back(_S_fopcode_restore_cur_results, + static_cast<_StateIdT>(__state._M_subexpr), + __res.second); + _M_frames.back()._M_subexpr_end = true; + _M_frames.back()._M_matched = __res.matched; + } + __res.second = _M_current; __res.matched = true; - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - inline void _Executor<_BiIter, _Alloc, _TraitsT>:: + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_line_begin_assertion(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; if (_M_at_begin()) - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - inline void _Executor<_BiIter, _Alloc, _TraitsT>:: + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_line_end_assertion(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; if (_M_at_end()) - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - inline void _Executor<_BiIter, _Alloc, _TraitsT>:: + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_word_boundary(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; if (_M_word_boundary() == !__state._M_neg) - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; + return _S_invalid_state_id; } // Here __state._M_alt offers a single start node for a sub-NFA. // We recursively invoke our algorithm to match the sub-NFA. template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: + _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_subexpr_lookahead(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; if (_M_lookahead(__state._M_alt) == !__state._M_neg) - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_match(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; if (_M_current == _M_end) - return; + return _S_invalid_state_id; if (_M_search_mode == _Search_mode::_DFS) { if (__state._M_matches(*_M_current)) { ++_M_current; - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } } else if (__state._M_matches(*_M_current)) _M_match_queue.emplace_back(__state._M_next, _M_cur_results); + + return _S_invalid_state_id; } template<typename _BiIter, typename _TraitsT> @@ -462,7 +497,7 @@ namespace __detail // (_M_current, _M_current + (__submatch.second - __submatch.first)). // If matched, keep going; else just return and try another state. template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: + _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_backref(_Match_mode, _StateIdT __i) { __glibcxx_assert(_M_search_mode == _Search_mode::_DFS); @@ -470,7 +505,7 @@ namespace __detail const auto& __state = _M_nfa[__i]; auto& __submatch = _M_cur_results[__state._M_backref_index]; if (!__submatch.matched) - return; + return _S_invalid_state_id; auto __last = _M_current; for (auto __tmp = __submatch.first; __last != _M_end && __tmp != __submatch.second; @@ -482,12 +517,17 @@ namespace __detail __submatch.first, __submatch.second, _M_current, __last)) { _M_current = __last; - _M_frames.emplace_back(_S_fopcode_next, __state._M_next); + return __state._M_next; } + + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_accept(_Match_mode __match_mode, _StateIdT) { if (_M_search_mode == _Search_mode::_DFS) @@ -528,7 +568,7 @@ namespace __detail { if (_M_current == _M_begin && (_M_flags & regex_constants::match_not_null)) - return; + return _S_invalid_state_id; if (__match_mode == _Match_mode::_Prefix || _M_current == _M_end) if (!_M_has_sol) { @@ -536,10 +576,14 @@ namespace __detail _M_results = _M_cur_results; } } + return _S_invalid_state_id; } template<typename _BiIter, typename _Alloc, typename _TraitsT> - void _Executor<_BiIter, _Alloc, _TraitsT>:: +#ifdef __OPTIMIZE__ + [[__gnu__::__always_inline__]] +#endif + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_handle_alternative(_Match_mode, _StateIdT __i) { const auto& __state = _M_nfa[__i]; @@ -549,7 +593,7 @@ namespace __detail // Pick lhs if it matches. Only try rhs if it doesn't. _M_frames.emplace_back(_S_fopcode_fallback_next, __state._M_next, _M_current); - _M_frames.emplace_back(_S_fopcode_next, __state._M_alt); + return __state._M_alt; } else { @@ -557,7 +601,7 @@ namespace __detail // See "case _S_opcode_accept:" handling above. _M_frames.emplace_back(_S_fopcode_posix_alternative, __state._M_next, _M_current); - _M_frames.emplace_back(_S_fopcode_next, __state._M_alt); + return __state._M_alt; } } @@ -565,54 +609,69 @@ namespace __detail #ifdef __OPTIMIZE__ [[__gnu__::__always_inline__]] #endif - inline void _Executor<_BiIter, _Alloc, _TraitsT>:: + inline _StateIdT _Executor<_BiIter, _Alloc, _TraitsT>:: _M_node(_Match_mode __match_mode, _StateIdT __i) { - if (_M_visited(__i)) - return; + // DFS has no _M_visited implementation as such don't even have the branch + // or the check in the call graph. + if (_M_search_mode == _Search_mode::_BFS) + if (_M_visited(__i)) + return _S_invalid_state_id; + _StateIdT __next = _S_invalid_state_id; switch (_M_nfa[__i]._M_opcode()) { case _S_opcode_repeat: - _M_handle_repeat(__match_mode, __i); break; + __next = _M_handle_repeat(__match_mode, __i); break; case _S_opcode_subexpr_begin: - _M_handle_subexpr_begin(__match_mode, __i); break; + __next = _M_handle_subexpr_begin(__match_mode, __i); + break; case _S_opcode_subexpr_end: - _M_handle_subexpr_end(__match_mode, __i); break; + __next = _M_handle_subexpr_end(__match_mode, __i); + break; case _S_opcode_line_begin_assertion: - _M_handle_line_begin_assertion(__match_mode, __i); break; + __next = _M_handle_line_begin_assertion(__match_mode, __i); break; case _S_opcode_line_end_assertion: - _M_handle_line_end_assertion(__match_mode, __i); break; + __next = _M_handle_line_end_assertion(__match_mode, __i); break; case _S_opcode_word_boundary: - _M_handle_word_boundary(__match_mode, __i); break; + __next = _M_handle_word_boundary(__match_mode, __i); break; case _S_opcode_subexpr_lookahead: - _M_handle_subexpr_lookahead(__match_mode, __i); break; + __next = _M_handle_subexpr_lookahead(__match_mode, __i); break; case _S_opcode_match: - _M_handle_match(__match_mode, __i); break; + __next = _M_handle_match(__match_mode, __i); break; case _S_opcode_backref: if (_M_search_mode == _Search_mode::_DFS) - _M_handle_backref(__match_mode, __i); + __next = _M_handle_backref(__match_mode, __i); else __builtin_unreachable(); break; case _S_opcode_accept: - _M_handle_accept(__match_mode, __i); break; + __next = _M_handle_accept(__match_mode, __i); break; case _S_opcode_alternative: - _M_handle_alternative(__match_mode, __i); break; + __next = _M_handle_alternative(__match_mode, __i); break; default: __glibcxx_assert(false); } + return __next; } template<typename _BiIter, typename _Alloc, typename _TraitsT> void _Executor<_BiIter, _Alloc, _TraitsT>:: _M_dfs(_Match_mode __match_mode, _StateIdT __start) { - const bool __dfs_mode = (_M_search_mode == _Search_mode::_DFS); - _M_frames.emplace_back(_S_fopcode_next, __start); + _StateIdT __next = __start; - while (!_M_frames.empty()) + while (true) { + // Follow immediate successors without re-entering the frame + // loop until we fail. This avoids the needless state save and + // restore through memory. + while (__next != _S_invalid_state_id) + __next = _M_node(__match_mode, __next); + + if (_M_frames.empty()) + break; + _ExecutorFrame<_BiIter> __frame = std::move(_M_frames.back()); _M_frames.pop_back(); @@ -621,27 +680,27 @@ namespace __detail case _S_fopcode_fallback_next: if (_M_has_sol) break; - if (__dfs_mode) + if (_M_search_mode == _Search_mode::_DFS) _M_current = __frame._M_pos; [[__fallthrough__]]; case _S_fopcode_next: - _M_node(__match_mode, __frame._M_state_id); + __next = __frame._M_state_id; break; case _S_fopcode_fallback_rep_once_more: if (_M_has_sol) break; - if (__dfs_mode) + if (_M_search_mode == _Search_mode::_DFS) _M_current = __frame._M_pos; [[__fallthrough__]]; case _S_fopcode_rep_once_more: - _M_rep_once_more(__match_mode, __frame._M_state_id); + __next = _M_rep_once_more(__match_mode, __frame._M_state_id); break; case _S_fopcode_posix_alternative: _M_frames.emplace_back(_S_fopcode_merge_sol, 0, _M_has_sol); - _M_frames.emplace_back(_S_fopcode_next, __frame._M_state_id); - if (__dfs_mode) + __next = __frame._M_state_id; + if (_M_search_mode == _Search_mode::_DFS) _M_current = __frame._M_pos; _M_has_sol = false; break;
