As mentioned in the comments, extractelement is special
since we actually want a scalar base for that element we extracted from
the vector (i.e. not a vector base).
This same logic should apply to uses of the extractelement such as phis
and selects which have the same BDV as the extractelement.
Added testcase showcases the problem where the BDV identification chokes
on the incorrect cast from vector to scalar for the phi use of
Tests-Run: make check