1. Fix some bugs in the jump table lowering threshold
2. Implement much better metric for optimal pivot selection
3. Tune thresholds for different lowering methods
4. Implement shift-and trick for lowering small (<machine word
length) cases with few destinations. Good testcase will follow.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35816 91177308-0d34-0410-b5e6-96231b3b80d8
