IR is now always parsed in opaque pointer mode, unless
-opaque-pointers=0 is explicitly given. There is no automatic
detection of typed pointers anymore.

The -opaque-pointers=0 option is added to any remaining IR tests
that haven't been migrated yet.

Differential Revision: https://reviews.llvm.org/D141912

Tests relying on this should explicitly use -passes='require<analysis>,foo'.

This simplifies the return value of addRuntimeCheck from a pair of
instructions to a single `Value *`.

The existing users of addRuntimeChecks were ignoring the first element
of the pair, hence there is not reason to track FirstInst and return
it.

Additionally all users of addRuntimeChecks use the second returned
`Instruction *` just as `Value *`, so there is no need to return an
`Instruction *`. Therefore there is no need to create a redundant
dummy `and X, true` instruction any longer.

Effectively this change should not impact the generated code because the
redundant AND will be folded by later optimizations. But it is easy to
avoid creating it in the first place and it allows more accurately
estimating the cost of the runtime checks.

The exit blocks of the versioned and non-versioned loops are not dedicated and thus the two loops are not in simplify form.
Insert dummy exit blocks after loop versioning with `formDedicatedExits()` to preserve the simplify form for subsequence passes.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D89569

Reviewed By: ychen, fhahn

Differential Revision: https://reviews.llvm.org/D85063

Follow-up to D82607
Revert an accidental change (empty.ll) of D82683

The reversion apparently deleted the test/Transforms directory.

Will be re-reverting again.

llvm-svn: 358552