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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111060 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/Local.cpp

@@ -490,6 +490,9 @@ static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
 /// rewriting all the predecessors to branch to the successor block and return
 /// true.  If we can't transform, return false.
 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
+  assert(BB != &BB->getParent()->getEntryBlock() &&
+         "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
+
   // We can't eliminate infinite loops.
   BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
   if (BB == Succ) return false;