LICM uses AliasSet information to hoist and sink instructions. However, other passes, such as LoopRotate

may invalidate its AliasSet because SSAUpdater does not update the AliasSet properly.
This patch teaches SSAUpdater to notify AliasSet that it made changes.
The testcase in PR12901 is too big to be useful and I could not reduce it to a normal size. 

rdar://11872059 PR12901

llvm-svn: 161803

llvm/include/llvm/Support/ValueHandle.h

@@ -110,11 +110,12 @@ protected:
            V != DenseMapInfo<Value *>::getTombstoneKey();
   }
 
-private:
+public:
   // Callbacks made from Value.
   static void ValueIsDeleted(Value *V);
   static void ValueIsRAUWd(Value *Old, Value *New);
 
+private:
   // Internal implementation details.
   ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
   HandleBaseKind getKind() const { return PrevPair.getInt(); }

llvm/lib/Transforms/Utils/SSAUpdater.cpp

@@ -214,6 +214,11 @@ void SSAUpdater::RewriteUse(Use &U) {
   else
     V = GetValueInMiddleOfBlock(User->getParent());
 
+  // Notify that users of the existing value that it is being replaced.
+  Value *OldVal = U.get();
+  if (OldVal != V && OldVal->hasValueHandle())
+    ValueHandleBase::ValueIsRAUWd(OldVal, V);
+
   U.set(V);
 }