[SCEV] Fix getLoopBackedgeTakenCounts

The way `getLoopBackedgeTakenCounts` is written right now isn't
correct. It will try to compute and store the BE counts of a Loop
 #{child loop} number of times (which may be zero).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256338 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed