[LV] Add initial legality checks for loops with unbound loads. (#152422)

This patch splits out the legality checks from PR #151300, following the
landing of PR #128593.

It is a step toward supporting vectorization of early-exit loops that
contain potentially faulting loads.
In this commit, an early-exit loop is considered legal for vectorization
if it satisfies the following criteria:

1. it is a read-only loop.
2. all potentially faulting loads are unit-stride, which is the only
type currently supported by vp.load.ff.

0 files changed, 0 insertions, 0 deletions