Similar to mask-load/store and compress/expand, the gather and
scatter operation now allow for higher dimension uses. Note that
to support the mixed-type index, the new syntax is:
vector.gather %base [%i,%j] [%kvector] ....
The first client of this generalization is the sparse compiler,
which needs to define scatter and gathers on dense operands
of higher dimensions too.
Reviewed By: bixia
Differential Revision: https://reviews.llvm.org/D97422
df5ccf5a94