false positive uninit reads in recent clang std::vector<bool>

[derekbruening]

It looks like recent clang:
Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
is using bitvectors for std::vector and they thwart DrMem's bit
handling.

~~Dr.M~~ Error #1: UNINITIALIZED READ: reading register esi
~~Dr.M~~ # 0 Board::getHorizontalWall               [/Applications/Xcode.app/Contents/Developer/Too\
lchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__bit_reference:145]
~~Dr.M~~ # 1 Board::moveRobot                       [board_solution.cpp:226]
~~Dr.M~~ # 2 TryAllMoveSequences                    [main_solution.cpp:208]
~~Dr.M~~ # 3 main                                   [main_solution.cpp:295]

Zooming in on the code involved:

    while (getHorizontalWall(location.row+0.5,location.col) == false &&
           getspot(Position(location.row+1,location.col)) == ' ') {

  horizontal_walls = std::vector<std::vector<bool> >(rows+1,std::vector<bool>(cols,false));

  return horizontal_walls[floor(r)][c-1];

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c\
++/v1/__bit_reference:145
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR operator bool() const _NOEXCEPT                     
        {return static_cast<bool>(*__seg_ & __mask_);}

So this C++ lib is taking vector and squishing it into a bit array.

I have yet to construct a small reproducer (unless I turn on -strict_bitops).

[derekbruening]

Xref issue #1451