add a new method.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20293 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/BasicBlock.h

@@ -107,7 +107,12 @@ public:
   ///
   void eraseFromParent();
 
-
+  /// getSinglePredecessor - If this basic block has a single predecessor block,
+  /// return the block, otherwise return a null pointer.
+  BasicBlock *getSinglePredecessor();
+  const BasicBlock *getSinglePredecessor() const {
+    return const_cast<BasicBlock*>(this)->getSinglePredecessor();
+  }
 
   //===--------------------------------------------------------------------===//
   /// Instruction iterator methods