[GlobalISel] Add support for switch statements

This commit does this using a trivial chain of conditional branches.  In the
future, we probably want to reuse the optimized switch lowering used in
SelectionDAG.

Differential Revision: https://reviews.llvm.org/D28176



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291099 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed