Teach SimplifyCFG how to simplify indirectbr instructions.
 - Eliminate redundant successors.
 - Convert an indirectbr with one successor into a direct branch.

Also, generalize SimplifyCFG to be able to be run on a function entry block.
It knows quite a few simplifications which are applicable to the entry
block, and it only needs a few checks to avoid trouble with the entry block.

llvm-svn: 111060
GitOrigin-RevId: 4a63fad976c8cf3bcdc1bbc3927668164890ecb8
6 files changed