[ShrinkWrap] Refactor the handling of infinite loop in the analysis.

[ShrinkWrap] Refactor the handling of infinite loop in the analysis.
- Strenghten the logic to be sure we hoist the restore point out of the current
  loop. (The fixes a bug with infinite loop, added as part of the patch.)
- Walk over the exit blocks of the current loop to conver to the desired restore
  point in one iteration of the update loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247958 91177308-0d34-0410-b5e6-96231b3b80d8