Fix build errors introduced by r235215

Fix build errors introduced by r235215

Summary:
- Handle TypePromoteFloat in switch statements
- Move an expression into an assert to avoid unused variable in
  non-assert builds.

Reviewers: srhines, ab

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9086

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235220 91177308-0d34-0410-b5e6-96231b3b80d8