[PATCH][libcxx] Prevent '\b' from backing up into invalid memory (case 2)

[William Fisher]

This patch fixes a less likely case where '\b' can back up into invalid
memory, when driven by a regex_iterator (for case 1, see r185273 or
http://llvm.org/bugs/show_bug.cgi?id=16240)

The attached test program also supplies a test for the case 1 fix in
r185273.

Thanks,
-Bill

#include <regex>
#include <string>
#include <list>
#include <cassert>

int main()
{
    // This regex_iterator uses regex_search(__wrap_iter<_Iter> __first, ...)
    // Test for http://llvm.org/bugs/show_bug.cgi?id=16240 fixed in r185273.
    {
        std::string s{"aaaa a"};
        std::regex re{"\\ba"};
        std::sregex_iterator it{s.begin(), s.end(), re};
        std::sregex_iterator end{};

        assert(it->position(0) == 0);
        assert(it->length(0) == 1);

        ++it;
        assert(it->position(0) == 5);
        assert(it->length(0) == 1);

        ++it;
        assert(it == end);
    }

    // This regex_iterator uses regex_search(_BidirectionalIterator __first, ...)
    {
        std::string s{"aaaa a"};
        std::list<char> l{s.begin(), s.end()};
        std::regex re{"\\ba"};
        std::regex_iterator<std::list<char>::iterator> it{l.begin(), l.end(), re};
        std::regex_iterator<std::list<char>::iterator> end{};

        assert(it->position(0) == 0);
        assert(it->length(0) == 1);

        ++it;
        assert(it->position(0) == 5);
        assert(it->length(0) == 1);

        ++it;
        assert(it == end);
    }
}

regex_search.patch
Description: Binary data

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