Runtime error check elimination

Runtime error check elimination

  Hoist runtime checks in the loop nest if they guard an "error" like event.
  Such events are recognized as blocks with an unreachable terminator or a call
  to the ubsan function that deals with out of bound accesses. Other "error"
  events can be added easily.

  We will ignore these blocks when we detect/model/optmize and code generate SCoPs
  but we will make sure that they would not have been executed using the assumption
  framework.

llvm-svn: 247310