[libc++] std::regex match_prev_avail implementation is regressed #74838
Description
It seems match_prev_avail implementation is regressed after fixed issue #41544.
test cases:
#include <string>
#include <regex>
#include <iostream>
using namespace std;
int main() {
string s = "ab";
string::iterator start = s.begin() + 1;
regex re0("^");
cout << "^" << endl;
cout << regex_search(start, s.end(), re0, regex_constants::match_default) << endl;
cout << regex_search(start, s.end(), re0, regex_constants::match_not_bol) << endl;
cout << regex_search(start, s.end(), re0, regex_constants::match_prev_avail) << endl;
cout << regex_search(start, s.end(), re0, regex_constants::match_prev_avail | regex_constants::match_not_bol) << endl;
// https://github.com/llvm/llvm-project/issues/41544
regex re1("^ab");
cout << "\n\n" << "^ab" << endl;
cout << regex_search(s, re1, regex_constants::match_default) << endl;
cout << regex_search(s, re1, regex_constants::match_not_bol) << endl;
cout << regex_search(s, re1, regex_constants::match_prev_avail) << endl;
cout << regex_search(s, re1, regex_constants::match_prev_avail | regex_constants::match_not_bol) << endl;
regex re2("^b");
cout << "\n\n" << "^b" << endl;
cout << regex_search(start, s.end(), re2, regex_constants::match_default) << endl;
cout << regex_search(start, s.end(), re2, regex_constants::match_not_bol) << endl;
cout << regex_search(start, s.end(), re2, regex_constants::match_prev_avail) << endl;
cout << regex_search(start, s.end(), re2, regex_constants::match_prev_avail | regex_constants::match_not_bol) << endl;
return 0;
}GCC (msys2 mingw64 13.2.0):
D:\notepad2>g++ -std=c++17 -Wall -Wextra test.cpp
D:\notepad2>a.exe
^
1
0
0
0
^ab
1
0
0
0
^b
1
0
0
0
MSVC (2022 17.8.3):
D:\notepad2>cl /nologo /EHsc /std:c++17 /W4 test.cpp
test.cpp
D:\notepad2>test.exe
^
1
0
0
0
^ab
1
0
0
0
^b
1
0
0
0
llvm-mingw 17.0.6 https://github.com/mstorsjo/llvm-mingw/releases/tag/20231128
D:\notepad2>clang++ -std=c++17 -Wall -Wextra test.cpp
D:\notepad2>a.exe
^
1
0
1
1
^ab
1
0
1
1
^b
1
0
1
1
based on https://sourceforge.net/p/scintilla/bugs/2405/?page=1#442d/89d2, libc++ (Xcode 15.0.1) on macOS also fails.