libstdc++/regex: Defer _M_current restoration to backtracking nodes [PR86164]

The incrementing of the current input string position (_M_current) 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.
In turn we can get rid of the now unused restore_current frame kind.

This reduces the maximum size of the _M_frames stack by 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.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

0 files changed, 0 insertions, 0 deletions