<regex>: Optimize matcher layout

[muellerj2]

This PR saves 8 bytes (x64 and x86) in the matcher by roughly ordering the members descendingly according to alignment. (I say roughly because some types are user-defined types, so their placement is a bit of a guess.)

Test program:

#include <iostream>
#include <regex>
#include <string>

using namespace std;

int main() {
    cout << "size const char*: " << sizeof(_Matcher3<const char*, char, regex_traits<char>, const char*, void>) << "\n";
    cout << "size string: " << sizeof(_Matcher3<string::iterator, char, regex_traits<char>, string::iterator, void>)
         << "\n";
    cout << "size const wchar_t*: "
         << sizeof(_Matcher3<const wchar_t*, wchar_t, regex_traits<wchar_t>, const wchar_t*, void>) << "\n";
    cout << "size wstring: " << sizeof(_Matcher3<wstring::iterator, wchar_t, regex_traits<wchar_t>, wstring::iterator, void>)
         << "\n";
}

Size comparison x64

Before:

size const char*: 256
size string: 256
size const wchar_t*: 256
size wstring: 256

After:

size const char*: 248
size string: 248
size const wchar_t*: 248
size wstring: 248

Size comparison x86

Before:

size const char*: 152
size string: 152
size const wchar_t*: 152
size wstring: 152

After:

size const char*: 144
size string: 144
size const wchar_t*: 144
size wstring: 144

[StephanTLavavej]

I also love that this consolidates the data members into a single place!

Layout looks good:

D:\GitHub\STL\out\x64>type meow.cpp
#include <regex>
using namespace std;
int main() {
    regex r{"a+"};
    (void) regex_match("a", r);
}

D:\GitHub\STL\out\x64>cl /EHsc /nologo /W4 /std:c++latest /MT /Od /c meow.cpp
meow.cpp

D:\GitHub\STL\out\x64>cl /EHsc /nologo /W4 /std:c++latest /MT /Od /c /d1reportSingleClassLayout_Matcher3 meow.cpp
meow.cpp

class std::_Matcher3<char const *,char,class std::regex_traits<char>,char const *,void> size(248):
        +---
 0      | _Complexity_limit
 8      | ?$_Tgt_state_v2_t@PEBDV?$allocator@PEBD@std@@ _Tgt_state
64      | ?$_Tgt_state_v2_t@PEBDV?$allocator@PEBD@std@@ _Res
120     | ?$_Rx_fixed_size_buffer@U?$_Loop_vals_v3_t@_J@std@@V?$allocator@U?$_Loop_vals_v3_t@_J@std@@@2@ _Loop_vals
144     | ?$_Rx_small_vector@V?$_Rx_state_frame_t@PEBD@std@@V?$allocator@V?$_Rx_state_frame_t@PEBD@std@@@2@ _Frames
176     | _Frames_count
184     | _Frames_limit
192     | _Start
200     | _Traits
208     | _Begin
216     | _End
224     | syntax_option_type _Sflags
228     | match_flag_type _Mflags
232     | _Ncap
236     | _Char_class_w
238     | _Char_class_s
240     | _Char_class_d
242     | _Matched
243     | _Longest
244     | _Full
        | <alignment member> (size=3)
        +---

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo. Please notify me if any further changes are pushed, otherwise no action is required.

[StephanTLavavej]

Thanks for getting everything tidied up for 14.51! 🎉 😻 🐈