libstdc++/regex: Replace __dfs_mode template parameter with run-time flag

That _Executor's __dfs_mode flag is a template parameter means
__regex_algo_impl has to instantiate two different (but largely the
same) versions of _Executor even though the BFS version is rarely used.
And it seems the compiler has trouble DCEing the unused version of
_Executor, which needlessly increases code size and burdens the optimizer.

This patch replaces the template parameter with a run-time data member
_M_search_mode.  We in turn need to inline the _Executor::_State_info
member functions and data members into _Executor so that they depend on
the run-time instead of compile-time flag.  This means _Executor is
three pointers bigger in DFS mode (due to the unused _M_match_queue and
_M_visited_states members), which we can reduce to one pointer if we
really want to, but that doesn't seem ver worthwhile.

The __dfs_mode template parameter is now unused but not yet removed,
that'll be done in the next patch.

After this patch, both code size and run time for the microbenchmark

    for (int i = 0; i < 10000; i++)
      regex_match(string(200, 'a'), regex("(a|b|c)*"));

decreases by about 15% each (with -O2).  Compile time/memory use decreases
by 5-10%.

libstdc++-v3/ChangeLog:

	* include/bits/regex.tcc (__regex_algo_impl): Pass __use_dfs
	parameter to _Executor's constructor.
	* include/bits/regex_executor.h (_Executor::_Search_mode): New.
	(_Executor::_Executor): Add __use_dfs parameter and initialize
	_M_search_mode.  Adjust after inlining _State_info members into
	_Executor.
	(_Executor::~_Executor): Free _M_visted_states.
	(_Executor::_M_main): Adjust after renaming _M_main_dispatch
	overloads to _M_main_dfs and _M_main_bfs.
	(_Executor::_State_info): Remove.
	(_Executor::_M_visited): Inlined from _State_info.
	(_Executor::_M_get_sol_pos): Likewise.
	(_Executor::_M_states): Remove.
	(_Executor::_M_start): Inlined from _State_info.
	(_Executor::_M_sol_pos): Likewise.
	(_Executor::_M_match_queue): Likewise.
	(_Executor::_M_search_mode): New.
	* include/bits/regex_executor.tcc (_Executor::_M_main_dispatch):
	Renamed to...
	(_Executor::_M_main_dfs, _Executor::_M_main_bfs): ... these.
	(_Executor::_M_*): Adjust after _M_states removal.
	(_Executor::_M_lookhead): Also adjust _Executor constructor
	call.

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

0 files changed, 0 insertions, 0 deletions