Some memory use + wall clock benchmarks for
regex_match(string(200000, 'a'), "(a|b|c)*"):
HEAD~4 | HEAD
+----------------+--------------+
-O0 | 150MB, 0.17s | 50MB, 0.31s |
+----------------+-------------+
-O2 | 100MB, 0.07s | 50MB, 0.05s |
+----------------+-------------+
So the only downside to this patch series is that at -O0 we're 1.8x slower
than before at -O0. According to perf this is due std::vector (e.g. 30%
of runtime is in back(), end() and empty()). That seems acceptable given the
50%-66% reduction in memory use (and with -O2 a slight speedup as well).
-- >8 --
The actual incrementing of the current input string position is done by
_M_handle_match which also makes sure to restore it afterwards, via a
restore_current frame. But restoring _M_current is naturally only
necessary when backtracking is involved, not after every single match.
So this patch moves the responsibility of saving/restoring _M_current
from _M_handle_match to the branching nodes _M_handle_alternative and
_M_handle_repeat. This is done by storing _M_current within the
fallback_next, fallback_rep_once_more and posix_alternative frames.
And we can get rid of the restore_current frame.
This reduces the maximum size of the __frames stack by a further 15% for
regex_match(string(200000, 'a'), "(a|b|c)*").
PR libstdc++/86164
libstdc++-v3/ChangeLog:
* include/bits/regex_executor.tcc (__detail::_ExecutorFrameOpcode):
Remove _S_fopcode_restore_current.
(__detail::_Executor::_M_handle_repeat): Pass _M_current when
pushing a fallback_next or fallback_rep_once_more frame.
(__detail::_Executor::_M_handle_match): Don't push a
restore_current frame.
(__detail::_Executor::_M_handle_backref): Likewise and simplify
accordingly.
(__detail::_Executor::_M_handle_alternative): Pass _M_current when
pushing a fallback_next or posix_alternative frame.
(__detail::_Executor::_M_dfs) <case _S_fopcode_fallback_next>:
Restore _M_current.
<case _S_fopcode_fallback_rep_once_more>: Likewise.
<case _S_fopcode_posix_alternative>: Likewise.
<case _S_fopcode_restore_current>: Remove.
---
libstdc++-v3/include/bits/regex_executor.tcc | 41 ++++++++++----------
1 file changed, 20 insertions(+), 21 deletions(-)
diff --git a/libstdc++-v3/include/bits/regex_executor.tcc
b/libstdc++-v3/include/bits/regex_executor.tcc
index ca631fb77ce9..7d32bc816a12 100644
--- a/libstdc++-v3/include/bits/regex_executor.tcc
+++ b/libstdc++-v3/include/bits/regex_executor.tcc
@@ -62,7 +62,6 @@ namespace __detail
_S_fopcode_fallback_rep_once_more,
_S_fopcode_posix_alternative,
_S_fopcode_merge_sol,
- _S_fopcode_restore_current,
_S_fopcode_restore_subexpr_begin,
_S_fopcode_restore_subexpr_end,
_S_fopcode_restore_rep_count_pos,
@@ -216,12 +215,14 @@ namespace __detail
// Greedy.
if (!__state._M_neg)
{
- __frames.emplace_back(_S_fopcode_fallback_next, __state._M_next);
+ __frames.emplace_back(_S_fopcode_fallback_next, __state._M_next,
+ _M_current);
__frames.emplace_back(_S_fopcode_rep_once_more, __i);
}
else // Non-greedy mode
{
- __frames.emplace_back(_S_fopcode_fallback_rep_once_more, __i);
+ __frames.emplace_back(_S_fopcode_fallback_rep_once_more, __i,
+ _M_current);
__frames.emplace_back(_S_fopcode_next, __state._M_next);
}
}
@@ -305,7 +306,6 @@ namespace __detail
return;
if (__state._M_matches(*_M_current))
{
- __frames.emplace_back(_S_fopcode_restore_current, 0, _M_current);
++_M_current;
__frames.emplace_back(_S_fopcode_next, __state._M_next);
}
@@ -382,14 +382,8 @@ namespace __detail
_M_re._M_automaton->_M_traits)._M_apply(
__submatch.first, __submatch.second, _M_current, __last))
{
- if (__last != _M_current)
- {
- __frames.emplace_back(_S_fopcode_restore_current, 0, _M_current);
- _M_current = __last;
- __frames.emplace_back(_S_fopcode_next, __state._M_next);
- }
- else
- __frames.emplace_back(_S_fopcode_next, __state._M_next);
+ _M_current = __last;
+ __frames.emplace_back(_S_fopcode_next, __state._M_next);
}
}
@@ -441,14 +435,16 @@ namespace __detail
if (_M_nfa._M_flags & regex_constants::ECMAScript)
{
// Pick lhs if it matches. Only try rhs if it doesn't.
- __frames.emplace_back(_S_fopcode_fallback_next, __state._M_next);
+ __frames.emplace_back(_S_fopcode_fallback_next, __state._M_next,
+ _M_current);
__frames.emplace_back(_S_fopcode_next, __state._M_alt);
}
else
{
// Try both and compare the result.
// See "case _S_opcode_accept:" handling above.
- __frames.emplace_back(_S_fopcode_posix_alternative, __state._M_next);
+ __frames.emplace_back(_S_fopcode_posix_alternative, __state._M_next,
+ _M_current);
__frames.emplace_back(_S_fopcode_next, __state._M_alt);
}
}
@@ -508,13 +504,19 @@ namespace __detail
case _S_fopcode_fallback_next:
if (!_M_has_sol)
- __frames.emplace_back(_S_fopcode_next, __frame._M_state_id);
+ {
+ _M_current = __frame._M_pos;
+ __frames.emplace_back(_S_fopcode_next, __frame._M_state_id);
+ }
break;
case _S_fopcode_fallback_rep_once_more:
if (!_M_has_sol)
- __frames.emplace_back(_S_fopcode_rep_once_more,
- __frame._M_state_id);
+ {
+ _M_current = __frame._M_pos;
+ __frames.emplace_back(_S_fopcode_rep_once_more,
+ __frame._M_state_id);
+ }
break;
case _S_fopcode_rep_once_more:
@@ -524,6 +526,7 @@ namespace __detail
case _S_fopcode_posix_alternative:
__frames.emplace_back(_S_fopcode_merge_sol, 0, _M_has_sol);
__frames.emplace_back(_S_fopcode_next, __frame._M_state_id);
+ _M_current = __frame._M_pos;
_M_has_sol = false;
break;
@@ -531,10 +534,6 @@ namespace __detail
_M_has_sol |= __frame._M_val;
break;
- case _S_fopcode_restore_current:
- _M_current = __frame._M_pos;
- break;
-
case _S_fopcode_restore_subexpr_begin:
_M_cur_results[__frame._M_state_id].first = __frame._M_pos;
break;
--
2.53.0.rc0.25.gb5c409c40f
