Previously reverted in 12696d302d
The arguments to a PHI may represent a recurrence by eventually using the output
of the PHI itself. This is now handled by checking for cycles in the control
flow. If a PHI is not in a recurrence, it is now able to report multiple offsets
instead of conservatively reporting unknown.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D138991