Add support to CallbackVH to receive notification when a Value's use-list changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122114 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/ValueHandle.h

@@ -105,6 +105,7 @@ private:
   // Callbacks made from Value.
   static void ValueIsDeleted(Value *V);
   static void ValueIsRAUWd(Value *Old, Value *New);
+  static void ValueAddedUse(Use &U);
 
   // Internal implementation details.
   ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
@@ -389,6 +390,11 @@ public:
   /// implemented as a CallbackVH, it would use this method to call
   /// setValPtr(new_value).  AssertingVH would do nothing in this method.
   virtual void allUsesReplacedWith(Value *) {}
+  
+  /// Called when a new Use is added to the use-list of this->getValPtr(),
+  /// after the Use has been appended to the list.  Other VH kinds would ignore
+  /// this callback, but clients can use it to trigger re-analysis of Values.
+  virtual void addedUse(Use &U) {}
 };
 
 // Specialize simplify_type to allow CallbackVH to participate in

include/llvm/Value.h

@@ -195,7 +195,7 @@ public:
 
   /// addUse - This method should only be used by the Use class.
   ///
-  void addUse(Use &U) { U.addToList(&UseList); }
+  void addUse(Use &U);
 
   /// An enumeration for keeping track of the concrete subclass of Value that
   /// is actually instantiated. Values of this enumeration are kept in the 

lib/VMCore/Value.cpp

@@ -281,6 +281,16 @@ void Value::takeName(Value *V) {
 }
 
 
+/// addUse - This method should only be used by the Use class.
+///
+void Value::addUse(Use &U) {
+  U.addToList(&UseList);
+  
+  // Notify all ValueHandles (if present) that this value added a Use.
+  if (HasValueHandle)
+    ValueHandleBase::ValueAddedUse(U);
+}
+
 // uncheckedReplaceAllUsesWith - This is exactly the same as replaceAllUsesWith,
 // except that it doesn't have all of the asserts.  The asserts fail because we
 // are half-way done resolving types, which causes some types to exist as two
@@ -569,6 +579,34 @@ void ValueHandleBase::ValueIsDeleted(Value *V) {
   }
 }
 
+void ValueHandleBase::ValueAddedUse(Use &U) {
+  assert(U->HasValueHandle && "Should only be called if ValueHandles present");
+
+  // Get the linked list base, which is guaranteed to exist since the
+  // HasValueHandle flag is set.
+  LLVMContextImpl *pImpl = U->getContext().pImpl;
+  ValueHandleBase *Entry = pImpl->ValueHandles[U.get()];
+
+  assert(Entry && "Value bit set but no entries exist");
+
+  // We use a local ValueHandleBase as an iterator so that
+  // ValueHandles can add and remove themselves from the list without
+  // breaking our iteration.  This is not really an AssertingVH; we
+  // just have to give ValueHandleBase some kind.
+  for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
+    Iterator.RemoveFromUseList();
+    Iterator.AddToExistingUseListAfter(Entry);
+    assert(Entry->Next == &Iterator && "Loop invariant broken.");
+
+    switch (Entry->getKind()) {
+    default:
+      break;
+    case Callback:
+      static_cast<CallbackVH*>(Entry)->addedUse(U);
+      break;
+    }
+  }
+}
 
 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");