Bug 83239 - False positive from -Wstringop-overflow on simple
std::vector code, besides pointing out the warning, suggests
a missed optimization opportunity. This is the second report
involving for vector (the last one was pr79095) with the same
symptoms and a similar root cause. Since the information GCC
keeps about pointers is limited, it's difficult to determine
that their relationship is p <= q <= r. This is exacerbated
by the fact that GCC doesn't know that the difference between
any two pointers into the same object cannot be greater than
PTRDIFF_MAX (bug 79119).
To help GCC generate better code and avoid the false positive,
the attached patch adds simple instrumentation to
vector::_M_default_append() asserting the important pointer
relationships.