This reverts commit 31abf0774232735ad7a7d45e531497305bf99fae.

This reverts commit 1268352656f81ea173860a8002aadb88844137e7.

This patch implements a simple pass that tries to de-duplicate packs. If
there are two packing patterns inserting the exact same values in the
exact same order, then we will keep the top-most one of them. Even
though such patterns may be optimized away by subsequent passes it is
still useful to do this within the vectorizer because otherwise the cost
estimation may be off, making the vectorizer over conservative.

This patch adds a region pass that reverts the IR state unconditionally.
This is used for testing.

This patch implements a simple printing pass for regions. This is meant
to be used in tests and for debugging.

RegionFromBBs is a helper Sandbox IR function pass that builds a region
for each BB. This helps test region passes in isolation without relying
on other parts of the vectorizer, which is especially useful for
stress-testing.

This patch fixes the value we generate when we vectorize constants.

This patch adds a helper flag for bisection debugging. This flag
force-stops vectorization after this many bundles have been considered
for vectorization.
Using -sbvec-stop-bndl=0 will not vectorize the code at all.

This new option lets you specify an allow-list of source files and
disables vectorization if the IR is not in the list. This can be used
for debugging miscompiles.

When debugging miscompiles we need a way to force-stop the vectorizer
early. This helps figure out which invocation is generating incorrect
code.