std::vector::_Insert() contains a suboptimal check against max_size by Dmitry Me

As of version 10.0.40219.1 SP1Rel std::vector::_Insert() code goes like this:

if (_Count == 0)
;
else if (max_size() - size() < _Count)
_Xlen();    // result too long
else if (capacity() < size() + _Count)
{    // not enough room, reallocate
//skipped
}
else
{    // new stuff fits, append and rotate into place
//skipped
}

Now capacity() <= max_size() at all times. Which means that if capacity() >= size() + _Count (enough room) then automatically max_size() >= size() + _Count. Which means that whenever that code is invoked when a vector already has room (that's quite often) the check max_size() >= size() + _Count is redundant.

_Insert() should be redesigned like this:

if (_Count == 0)
;
else if (capacity() - size() < _Count)
{
    if (max_size() - size() < _Count)
        _Xlen();    // result too long
    // not enough room, reallocate
    //skipped
}else
{    // new stuff fits, append and rotate into place
//skipped
}

so that the check is done only if there's a need for reallocation in the first place.