On Thu, 29 Jan 2026, Jonathan Wakely wrote:
> On Wed, 28 Jan 2026 at 11:27 -0500, Patrick Palka wrote:
> > Changes in v7:
> > - Make fallback_next and fallback_rep_once_more code paths fall through
> > to the next / rep_once_more code paths instead of pushing a frame
> > that gets immediately popped.
> >
> > Changes in v6:
> > - Use an inline namespace to give the _Executor class a different
> > mangled name since its implementation is no longer compatible with
> > the previous recursive one
> > - Explicitly cast _M_subexpr to _StateIdT in _M_handle_subexpr_begin/end
> > to self-document that what we're storing in _ExecutorFrame::_M_state_id
> > isn't really a state id
> > - I experimented with using std::deque instead of std::vector for the
> > frames stack.
> > Upsides:
> > - Reduces peak memory use from 50MB to 33MB for the microbenchmark
> > regex_match(string(200000, 'a'), "(a|b|c)*")
> > due to less unused capacity (vector's 2x growth factor means that
> > 50% of the time there will be at least 25% unused capacity)
> > - Seems to be as fast as vector
> > - Automatically reclaims unused capacity as the stack unwinds
> > - No expensive reallocation needed when growing the stack in the
> > case of non-trivially-copyable input iterators
> > Downsides:
> > - deque will allocate/free a chunk of memory whenever crossing a
> > chunk boundary (512 elements) in either direction, which could
> > degrade performance in rare cases where our stack size hovers
> > near a multiple of the chunk boundary.
> > - the fixed chunk size means small inputs will use at least
> > 512*24 bytes=12kB of memory
> > Ultimately it seems using std::deque is better for very large
> > inputs, and for small inputs std::vector is slightly better. I'm
> > not sure which container to go with, for now I stuck with std::vector.
> > (N.B. we seem to be 2x faster than libc++'s std::regex and use 60%
> > less memory for the above microbenchmark)
>
> Another option would be to stick with vector, but manage the capacity
> semi-manually. So when emplacing N new frames (where N == 1 or N == 2)
> check if we have capacity and if not, call
>
> _M_frames.reserve(_M_frames.size() * 3 / 2 + N);
>
> This would grow by a factor of 1.5 which would result in less overhead
> when we actually only need a tiny bit more capacity, and is claimed to
> be a better choice anyway:
> https://github.com/facebook/folly/blob/main/folly/docs/FBVector.md#memory-handling
>
> Maybe put that inside a _M_reserve_frames member so that any function
> which wants to call _M_frames.emplace_back would call
> _M_reserve_frames(1) or _M_reserve_frames(2) and inside that function
> it would do the check to see if it needs to increase the capacity.
>
> That can be a follow-up patch though, using vector is fine for this
> patch.
Will experiment with this as a follow-up
>
> > Changes in v5:
> > - Replace char _ExecutorFrame::_M_char with
> > uint8_t _ExecutorFrame::_M_bytes[7] to fully account for
> > the implicit struct padding and make it char size/signedness
> > agnostic.
> >
> > Changes in v4:
> > - Do not remove the BFS executor. I convinced myself that it's
> > worthwhile to keep it around for backwards compatibility and its
> > better time complexity (e.g. for PR78276).
> > - However, this means the mangling of _Executor is now the same as
> > before (since the __dfs_mode template parameter is no longer gone).
> > I believe we need to give this class a different mangling so
> > programs that mix old/new std::regex impls continue to work.
> >
> > Changes in v3:
> >
> > - Add char _M_char member to _ExecutorFrame (without increasing the
> > size of struct thanks to padding)
> > - Use it to fix bug in restore_subexpr_end frame code whereby we
> > weren't restoring _M_cur_results.matched properly
> > - Combine restore_subexpr_begin/end frame codes into one
> > restore_cur_results frame code
> > - Combine restore_rep_count_val/posn frame codes into single
> > restore_rep_count frame_code (this makes the patch 3/4 from v2
> > obsolete)
> > - Store the frame stack in the data member _ExecutorFrame::_M_frames
> > alongside the rest of the executor state instead of using a local.
> > Using a local variable is just more code with no real benefit.
> >
> > -- >8 --
> >
> > libstdc++/regex: Convert DFS executor to use iteration [PR86164]
> >
> > This replaces the recursion and implicit system stack usage of the DFS
> > executor with iteration and an explicit heap-based stack. After this
> > patch, we no longer stack overflow on the PR86164 testcases since system
> > stack usage is no longer linear with respect to input size. This should
> > otherwise be a non-functional change.
>
> This is so cool. Much simpler and cleaner than my abandoned attempt to
> do this - and with the added benefit that it actually works!
>
> > PR libstdc++/86164
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/regex.h (__detail::_Executor): Use inline
> > namespace _V2.
> > * include/bits/regex_executor.h (__detail::_ExecutorFrame):
> > Declare.
> > (__detail::_Executor): Use inline namespace _V2.
> > (__detail::_Executor::_M_node): Declare.
> > (__detail::_Executor::_M_frames): New data member.
> > * include/bits/regex_executor.tcc (__detail::_ExecutorFrameOpcode):
> > New.
> > (__detail::_ExecutorFrame): New.
> > (__detail::_Executor): Use inline namespace _V2.
> > (__detail::_Executor::_M_rep_once_more): Replace recursive
> > _M_dfs calls with an _S_opcode_next frame push, and any tail work
> > after such calls with an appropriate frame push.
> > (__detail::_M_handle_repeat): Likewise.
> > (__detail::_M_handle_subexpr_begin): Likewise.
> > (__detail::_M_handle_subexpr_end): Likewise.
> > (__detail::_M_handle_line_begin_assertion): Likewise.
> > (__detail::_M_handle_line_end_assertion): Likewise.
> > (__detail::_M_handle_word_boundary): Likewise.
> > (__detail::_M_handle_subexpr_lookahead): Likewise.
> > (__detail::_M_handle_match): Likewise.
> > (__detail::_M_handle_backref): Likewise.
> > (__detail::_M_handle_accept): Likewise.
> > (__detail::_M_handle_alternative): Likewise.
> > (__detail::_M_node): Factored out from _M_dfs.
> > (__detail::_M_dfs): Push an initial frame to _M_frames that
> > visits the starting node and pass this stack each subroutine.
> > Pop the latest _ExecutorFrame from _M_frames and handle
> > appropriately according to its _ExecutorFrameOpcode. Loop until
> > _M_frames is empty.
> > * include/std/regex: Include <cstdint>.
> > ---
> > libstdc++-v3/include/bits/regex.h | 2 +
> > libstdc++-v3/include/bits/regex_executor.h | 9 +
> > libstdc++-v3/include/bits/regex_executor.tcc | 218 +++++++++++++++----
> > libstdc++-v3/include/std/regex | 1 +
> > 4 files changed, 185 insertions(+), 45 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/regex.h
> > b/libstdc++-v3/include/bits/regex.h
> > index 68fb6254f362..5bcb9a447ce2 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, bool>
> > 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 f9857bfc4c1d..94048e1f632c 100644
> > --- a/libstdc++-v3/include/bits/regex_executor.h
> > +++ b/libstdc++-v3/include/bits/regex_executor.h
> > @@ -36,11 +36,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >
> > namespace __detail
> > {
> > +_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
> > /**
> > * @addtogroup regex-detail
> > * @{
> > */
> >
> > + template<typename _BiIter, bool _Trivial =
> > is_trivially_copyable<_BiIter>::value>
>
> I wondered if trivially-copyable is the right property, but I think it
> is close enough. I think the precise conditions for using this
> optimization are trivially move constructible, trivially move
> assignable, and trivially destructible. In practice, I think iterator
> types that satisfy those requirements but have non-trivial copy
> construction or non-trivial copy assignment (and so are not
> trivially-copyable) are unlikely. So using trivially-copyable is not
> likely to disable the optimization for any realistic types.
Also trivially copyable is already needed for fast std::vector
resizing so I figured might as well use the same property for this
optimization.
>
> > + struct _ExecutorFrame;
> > +
> > /**
> > * @brief Takes a regex and an input string and does the matching.
> > *
> > @@ -142,6 +146,9 @@ namespace __detail
> > void
> > _M_handle_alternative(_Match_mode, _StateIdT);
> >
> > + void
> > + _M_node(_Match_mode, _StateIdT);
> > +
> > void
> > _M_dfs(_Match_mode __match_mode, _StateIdT __start);
> >
> > @@ -290,6 +297,7 @@ namespace __detail
> > };
> >
> > public:
> > + _GLIBCXX_STD_C::vector<_ExecutorFrame<_BiIter>> _M_frames;
> > _ResultsVec _M_cur_results;
> > _BiIter _M_current;
> > _BiIter _M_begin;
> > @@ -305,6 +313,7 @@ namespace __detail
> > };
> >
> > ///@} regex-detail
> > +_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > } // namespace __detail
> > _GLIBCXX_END_NAMESPACE_VERSION
> > } // namespace std
> > diff --git a/libstdc++-v3/include/bits/regex_executor.tcc
> > b/libstdc++-v3/include/bits/regex_executor.tcc
> > index 421e585f39d9..ddfdbb0cb751 100644
> > --- a/libstdc++-v3/include/bits/regex_executor.tcc
> > +++ b/libstdc++-v3/include/bits/regex_executor.tcc
> > @@ -36,6 +36,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > #pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
> > namespace __detail
> > {
> > +_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > bool __dfs_mode>
> > bool _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
> > @@ -55,6 +56,71 @@ namespace __detail
> > return false;
> > }
> >
> > + enum _ExecutorFrameOpcode : uint8_t
>
> Can we use unsigned char to avoid <cstdint> here?
Done
>
> > + {
> > + _S_fopcode_next,
> > + _S_fopcode_fallback_next,
> > + _S_fopcode_rep_once_more,
> > + _S_fopcode_fallback_rep_once_more,
> > + _S_fopcode_posix_alternative,
> > + _S_fopcode_merge_sol,
> > + _S_fopcode_restore_current,
> > + _S_fopcode_restore_cur_results,
> > + _S_fopcode_restore_rep_count,
> > + _S_fopcode_decrement_rep_count,
> > + };
> > +
> > + template<typename _BiIter, bool _Trivial /* =
> > is_trivially_copyable<_BiIter>::value */>
> > + struct _ExecutorFrame
> > + {
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i)
> > + : _M_op(__op), _M_state_id(__i)
> > + { }
> > +
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i, _BiIter __p)
> > + : _M_op(__op), _M_state_id(__i), _M_pos(__p)
> > + { }
> > +
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i, long __v)
> > + : _M_op(__op), _M_state_id(__i), _M_val(__v)
> > + { }
> > +
> > + _ExecutorFrameOpcode _M_op;
> > + uint8_t _M_bytes[7];
> > + _StateIdT _M_state_id;
> > + // _M_pos and _M_val are mutually exclusive, which the optimized
> > + // partial specialization below depends on.
> > + _BiIter _M_pos = _BiIter();
> > + long _M_val = 0;
> > + };
> > +
> > + // Space-optimized partial specialization for when the input iterator is
> > + // trivially copyable.
> > + template<typename _BiIter>
> > + struct _ExecutorFrame<_BiIter, true>
> > + {
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i)
> > + : _M_op(__op), _M_state_id(__i)
> > + { }
> > +
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i, _BiIter __p)
> > + : _M_op(__op), _M_state_id(__i), _M_pos(__p)
> > + { }
> > +
> > + _ExecutorFrame(_ExecutorFrameOpcode __op, _StateIdT __i, long __v)
> > + : _M_op(__op), _M_state_id(__i), _M_val(__v)
> > + { }
> > +
> > + _ExecutorFrameOpcode _M_op;
> > + uint8_t _M_bytes[7];
> > + _StateIdT _M_state_id;
> > + union
> > + {
> > + _BiIter _M_pos;
> > + long _M_val;
> > + };
> > + };
> > +
> > // The _M_main function operates in different modes, DFS mode or BFS mode,
> > // indicated by template parameter __dfs_mode, and dispatches to one of
> > the
> > // _M_main_dispatch overloads.
> > @@ -181,19 +247,20 @@ namespace __detail
> > auto& __rep_count = _M_rep_count[__i];
> > if (__rep_count.second == 0 || __rep_count.first != _M_current)
> > {
> > - auto __back = __rep_count;
> > + _M_frames.emplace_back(_S_fopcode_restore_rep_count,
> > + __i, __rep_count.first);
> > + _M_frames.back()._M_bytes[0] = __rep_count.second;
>
> __rep_count.second is never greater than 2, right? So always fits in
> uint8_t.
Yes
>
> I wondered about replacing _M_bytes[7] with a union like:
>
> union {
> unsigned char _M_bytes[7];
> struct { // Used by restore_rep_count frame
> unsigned char _M_rep_count : 2;
> };
> struct { // Used by restore_cur_results frame
> unsigned char _M_matched : 1;
> unsigned char _M_restore_first : 1;
> };
> };
>
> So that we use more precise names than just _M_bytes[0] (and could
> still extend it later with other alternatives if needed).
>
> This might be over-complicating things, but if we *did* want to do it,
> I think we should decide now because the difference between setting
> _M_bytes[0] = 0xff and setting _M_restore_first = true would not be
> compatible if we changed it later (old TUs might expect to find 0xff
> there and new TUs would only set one bit).
I think slightly more flexible would be:
union {
unsigned char _M_byte0;
struct { // Used by restore_rep_count frame
unsigned char _M_rep_count : 2;
};
struct { // Used by restore_cur_results frame
unsigned char _M_matched : 1;
unsigned char _M_restore_first : 1;
};
};
unsigned char _M_bytes[6];
So that we could decide how to use each byte independently of the other
(e.g. maybe one byte could be for universal flags that apply to every
code).
>
>
> > __rep_count.first = _M_current;
> > __rep_count.second = 1;
> > - _M_dfs(__match_mode, __state._M_alt);
> > - __rep_count = __back;
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_alt);
> > }
> > else
> > {
> > if (__rep_count.second < 2)
> > {
> > __rep_count.second++;
> > - _M_dfs(__match_mode, __state._M_alt);
> > - __rep_count.second--;
> > + _M_frames.emplace_back(_S_fopcode_decrement_rep_count, __i);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_alt);
> > }
> > }
> > }
> > @@ -208,23 +275,23 @@ namespace __detail
> > _M_handle_repeat(_Match_mode __match_mode, _StateIdT __i)
> > {
> > const auto& __state = _M_nfa[__i];
> > -
> > // Greedy.
> > if (!__state._M_neg)
> > {
> > - _M_rep_once_more(__match_mode, __i);
> > - // If it's DFS executor and already accepted, we're done.
> > - if (!__dfs_mode || !_M_has_sol)
> > - _M_dfs(__match_mode, __state._M_next);
> > + if constexpr (__dfs_mode)
> > + // If it's DFS executor and already accepted, we're done.
> > + _M_frames.emplace_back(_S_fopcode_fallback_next, __state._M_next);
> > + else
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_rep_once_more, __i);
> > }
> > else // Non-greedy mode
> > {
> > if constexpr (__dfs_mode)
> > {
> > // vice-versa.
> > - _M_dfs(__match_mode, __state._M_next);
> > - if (!_M_has_sol)
> > - _M_rep_once_more(__match_mode, __i);
> > + _M_frames.emplace_back(_S_fopcode_fallback_rep_once_more, __i);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> > else
> > {
> > @@ -233,12 +300,11 @@ namespace __detail
> > // be better by attempting its next node.
> > if (!_M_has_sol)
> > {
> > - _M_dfs(__match_mode, __state._M_next);
> > // DON'T attempt anything if it's already accepted. An
> > // accepted state *must* be better than a solution that
> > // matches a non-greedy quantifier one more time.
> > - if (!_M_has_sol)
> > - _M_rep_once_more(__match_mode, __i);
> > + _M_frames.emplace_back(_S_fopcode_fallback_rep_once_more,
> > __i);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> > }
> > }
> > @@ -250,12 +316,13 @@ namespace __detail
> > _M_handle_subexpr_begin(_Match_mode __match_mode, _StateIdT __i)
> > {
> > const auto& __state = _M_nfa[__i];
> > -
> > auto& __res = _M_cur_results[__state._M_subexpr];
> > - auto __back = __res.first;
> > + _M_frames.emplace_back(_S_fopcode_restore_cur_results,
> > + static_cast<_StateIdT>(__state._M_subexpr),
> > + __res.first);
> > + _M_frames.back()._M_bytes[0] = 0xff;
> > __res.first = _M_current;
> > - _M_dfs(__match_mode, __state._M_next);
> > - __res.first = __back;
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > @@ -264,13 +331,14 @@ namespace __detail
> > _M_handle_subexpr_end(_Match_mode __match_mode, _StateIdT __i)
> > {
> > const auto& __state = _M_nfa[__i];
> > -
> > auto& __res = _M_cur_results[__state._M_subexpr];
> > - auto __back = __res;
> > + _M_frames.emplace_back(_S_fopcode_restore_cur_results,
> > + static_cast<_StateIdT>(__state._M_subexpr),
> > + __res.second);
> > + _M_frames.back()._M_bytes[0] = __res.matched;
> > __res.second = _M_current;
> > __res.matched = true;
> > - _M_dfs(__match_mode, __state._M_next);
> > - __res = __back;
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > @@ -280,7 +348,7 @@ namespace __detail
> > {
> > const auto& __state = _M_nfa[__i];
> > if (_M_at_begin())
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > @@ -290,7 +358,7 @@ namespace __detail
> > {
> > const auto& __state = _M_nfa[__i];
> > if (_M_at_end())
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > @@ -300,7 +368,7 @@ namespace __detail
> > {
> > const auto& __state = _M_nfa[__i];
> > if (_M_word_boundary() == !__state._M_neg)
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > // Here __state._M_alt offers a single start node for a sub-NFA.
> > @@ -312,7 +380,7 @@ namespace __detail
> > {
> > const auto& __state = _M_nfa[__i];
> > if (_M_lookahead(__state._M_alt) == !__state._M_neg)
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > @@ -321,16 +389,15 @@ namespace __detail
> > _M_handle_match(_Match_mode __match_mode, _StateIdT __i)
> > {
> > const auto& __state = _M_nfa[__i];
> > -
> > if (_M_current == _M_end)
> > return;
> > if constexpr (__dfs_mode)
> > {
> > if (__state._M_matches(*_M_current))
> > {
> > + _M_frames.emplace_back(_S_fopcode_restore_current, 0,
> > _M_current);
> > ++_M_current;
> > - _M_dfs(__match_mode, __state._M_next);
> > - --_M_current;
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> > }
> > else
> > @@ -413,13 +480,12 @@ namespace __detail
> > {
> > if (__last != _M_current)
> > {
> > - auto __backup = _M_current;
> > + _M_frames.emplace_back(_S_fopcode_restore_current, 0,
> > _M_current);
> > _M_current = __last;
> > - _M_dfs(__match_mode, __state._M_next);
> > - _M_current = __backup;
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> > else
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_next);
> > }
> > }
> >
> > @@ -483,31 +549,26 @@ namespace __detail
> > _M_handle_alternative(_Match_mode __match_mode, _StateIdT __i)
> > {
> > const auto& __state = _M_nfa[__i];
> > -
> > if (_M_nfa._M_flags & regex_constants::ECMAScript)
> > {
> > // TODO: Fix BFS support. It is wrong.
> > - _M_dfs(__match_mode, __state._M_alt);
> > // Pick lhs if it matches. Only try rhs if it doesn't.
> > - if (!_M_has_sol)
> > - _M_dfs(__match_mode, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_fallback_next, __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_alt);
> > }
> > else
> > {
> > // Try both and compare the result.
> > // See "case _S_opcode_accept:" handling above.
> > - _M_dfs(__match_mode, __state._M_alt);
> > - auto __has_sol = _M_has_sol;
> > - _M_has_sol = false;
> > - _M_dfs(__match_mode, __state._M_next);
> > - _M_has_sol |= __has_sol;
> > + _M_frames.emplace_back(_S_fopcode_posix_alternative,
> > __state._M_next);
> > + _M_frames.emplace_back(_S_fopcode_next, __state._M_alt);
> > }
> > }
> >
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > bool __dfs_mode>
> > void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
> > - _M_dfs(_Match_mode __match_mode, _StateIdT __i)
> > + _M_node(_Match_mode __match_mode, _StateIdT __i)
> > {
> > if (_M_states._M_visited(__i))
> > return;
> > @@ -545,6 +606,72 @@ namespace __detail
> > }
> > }
> >
> > + template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > + bool __dfs_mode>
> > + void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
> > + _M_dfs(_Match_mode __match_mode, _StateIdT __start)
> > + {
> > + _M_frames.emplace_back(_S_fopcode_next, __start);
> > +
> > + while (!_M_frames.empty())
> > + {
> > + _ExecutorFrame<_BiIter> __frame = std::move(_M_frames.back());
> > + _M_frames.pop_back();
> > +
> > + switch (__frame._M_op)
> > + {
> > + case _S_fopcode_fallback_next:
> > + if (_M_has_sol)
> > + break;
> > + // fallthrough
>
> Bah, C++11 so we can't use [[fallthough]].
>
> We could use [[__fallthrough__]], but I don't think that has much
> benefit over the comment (which I assume Clang supports too).
Changed to use [[__fallthrough__]]
>
>
> > + case _S_fopcode_next:
> > + _M_node(__match_mode, __frame._M_state_id);
> > + break;
> > +
> > + case _S_fopcode_fallback_rep_once_more:
> > + if (_M_has_sol)
> > + break;
> > + // fallthrough
> > + case _S_fopcode_rep_once_more:
> > + _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);
> > + _M_has_sol = false;
> > + break;
> > +
> > + case _S_fopcode_merge_sol:
> > + _M_has_sol |= __frame._M_val;
> > + break;
> > +
> > + case _S_fopcode_restore_current:
> > + _M_current = __frame._M_pos;
> > + break;
> > +
> > + case _S_fopcode_restore_cur_results:
> > + if (__frame._M_bytes[0] == 0xff)
> > + _M_cur_results[__frame._M_state_id].first = __frame._M_pos;
> > + else
> > + {
> > + _M_cur_results[__frame._M_state_id].second = __frame._M_pos;
> > + _M_cur_results[__frame._M_state_id].matched =
> > __frame._M_bytes[0];
> > + }
> > + break;
> > +
> > + case _S_fopcode_restore_rep_count:
> > + _M_rep_count[__frame._M_state_id].first = __frame._M_pos;
> > + _M_rep_count[__frame._M_state_id].second = __frame._M_bytes[0];
> > + break;
> > +
> > + case _S_fopcode_decrement_rep_count:
> > + _M_rep_count[__frame._M_state_id].second--;
> > + break;
> > + }
> > + }
> > + }
> > +
> > // Return whether now is at some word boundary.
> > template<typename _BiIter, typename _Alloc, typename _TraitsT,
> > bool __dfs_mode>
> > @@ -569,6 +696,7 @@ namespace __detail
> >
> > return __left_is_word != __right_is_word;
> > }
> > +_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > } // namespace __detail
> > #pragma GCC diagnostic pop
> >
> > diff --git a/libstdc++-v3/include/std/regex b/libstdc++-v3/include/std/regex
> > index c8fecfb2ad7a..003499c1bab5 100644
> > --- a/libstdc++-v3/include/std/regex
> > +++ b/libstdc++-v3/include/std/regex
> > @@ -40,6 +40,7 @@
> > #else
> >
> > #include <bitset>
> > +#include <cstdint>
> > #include <locale>
> > #include <stack>
> > #include <stdexcept>
> > --
> > 2.53.0.rc1.65.gea24e2c554
> >
> >
>
>
