Move helper for getting a terminating musttail call to BasicBlock

No functional change.  To be used in future commits that need to look
for such instructions.

Reviewed By: rafael

Differential Revision: http://reviews.llvm.org/D4504

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215413 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/BasicBlock.h

@@ -23,6 +23,7 @@
 
 namespace llvm {
 
+class CallInst;
 class LandingPadInst;
 class TerminatorInst;
 class LLVMContext;
@@ -125,6 +126,14 @@ public:
   TerminatorInst *getTerminator();
   const TerminatorInst *getTerminator() const;
 
+  /// \brief Returns the call instruction marked 'musttail' prior to the
+  /// terminating return instruction of this basic block, if such a call is
+  /// present.  Otherwise, returns null.
+  CallInst *getTerminatingMustTailCall();
+  const CallInst *getTerminatingMustTailCall() const {
+    return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
+  }
+
   /// \brief Returns a pointer to the first instruction in this block that is
   /// not a PHINode instruction.
   ///