Devirtualizing Value destructor (PR889). Patch by Pawel Kunio!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44747 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/BasicBlock.h

@@ -65,6 +65,9 @@ private :
   BasicBlock(const BasicBlock &);     // Do not implement
   void operator=(const BasicBlock &); // Do not implement
 
+protected:
+  static void destroyThis(BasicBlock*);
+  friend class Value;
 public:
   /// Instruction iterators...
   typedef InstListType::iterator                              iterator;
@@ -76,7 +79,6 @@ public:
   ///
   explicit BasicBlock(const std::string &Name = "", Function *Parent = 0,
                       BasicBlock *InsertBefore = 0);
-  ~BasicBlock();
 
   /// getParent - Return the enclosing method, or null if none
   ///
@@ -206,6 +208,33 @@ private:
   const BasicBlock *getPrev() const { return Prev; }
 };
 
+/// DummyInst - An instance of this class is used to mark the end of the
+/// instruction list.  This is not a real instruction.
+class DummyInst : public Instruction {
+protected:
+  static void destroyThis(DummyInst* v) {
+    Instruction::destroyThis(v);
+  }
+  friend class Value;
+public:
+  DummyInst();
+
+  Instruction *clone() const {
+    assert(0 && "Cannot clone EOL");abort();
+    return 0;
+  }
+  const char *getOpcodeName() const { return "*end-of-list-inst*"; }
+
+  // Methods for support type inquiry through isa, cast, and dyn_cast...
+  static inline bool classof(const DummyInst *) { return true; }
+  static inline bool classof(const Instruction *I) {
+    return I->getOpcode() == OtherOpsEnd;
+  }
+  static inline bool classof(const Value *V) {
+    return isa<Instruction>(V) && classof(cast<Instruction>(V));
+  }
+};
+
 inline int 
 ilist_traits<Instruction>::getListOffset() {
   return BasicBlock::getInstListOffset();