Currently the SCEVExpander tries to re-use existing casts, even if they
are not exactly at the insertion point it was asked to create the cast.
To do so in some case, it creates a new cast at the insertion point and
updates all users to use the new cast.
This behavior is problematic, because it changes the IR outside of the
instructions created during the expansion. Therefore we cannot
completely undo all changes made during expansion.
This re-use should be only an extra optimization, so only using the new
cast in the expanded instructions should not be a correctness issue.
There are many cases equivalent instructions are created during
This has minor impact on the tests, but there is one LoopDistribute test
that checks explicitly that only the new value is used. For now I just
XFAIL'd the test.
Once SCEVExpanderCleaner is added, we could keep a mapping of
values to replace and apply them once the result is used.