* Pull range optimization code out into new InsertRangeTest function.

* Pull range optimization code out into new InsertRangeTest function.
* SubOne/AddOne functions always return ConstantInt, declare them as such
* Pull code for handling setcc X, cst, where cst is at the end of the range,
  or cc is LE or GE up earlier in visitSetCondInst.  This reduces #iterations
  in some cases.
* Fold: (div X, C1) op C2 -> range check, implementing div.ll:test6 - test9.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16588 91177308-0d34-0410-b5e6-96231b3b80d8