Revert "Revert "[SimplifyCFG] allow speculation of exactly one expensive instruction (PR24818)""

This reverts commit r258903 which reverted r255660.  r258903 was an
accidental commit and should not have been committed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258905 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed