[llvm-bugs] [Bug 30515] New: out of range iterator usage in getLongestCommonPrefixLen (r280895)

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30515

            Bug ID: 30515
           Summary: out of range iterator usage in
                    getLongestCommonPrefixLen (r280895)
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: yaron.keren at gmail.com
                CC: llvm-bugs at lists.llvm.org, vsk at apple.com
    Classification: Unclassified

getLongestCommonPrefixLen calls the three-argument version of std::mismatch:

        std::mismatch(Strings[0].begin(), Strings[0].end(), Strings[I].begin())

with this call, Strings[I].end() is *assumed* to be Strings[I].begin() +
Strings[0].end() - Strings[0].begin(), see:

http://en.cppreference.com/w/cpp/algorithm/mismatch
 If last2 is not provided (overloads (1-4)), it denotes first2 + (last1 -
first1).

in case String[I] is a prefix of Strings[0], std::mismatch will continue
increasing its iterator outside String[I]. This is caught by Visual C++ runtime
lib in debug mode, "string iterator + offset out of range". the code probably
works since the strings are null-terminated but at least VC thinks it is wrong.

the four-argument std::mismatch could solve this but sadly is C++ 17.
maybe it's best just to hardcode the while loop.

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