R600/SI: Only select SALU instructions in the entry or exit block

SALU instructions ignore control flow, so it is not always safe to use
them within branches.  This is a partial solution to this problem
until we can come up with something better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207590 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed