[MemorySSA] Remove optimized value when reseting optimized.

[asbirlea]

Summary

If we don't reset the optimized value O for access A, even though A is no longer optimized to O, A will still show up in that O's users list.
This fails verification when hoisting a Def outside a loop, even though the updates are correct.
The reason is that the phi in the loop header still find as user the hoisted def, because the Def has a pointer to the Phi in its optimized operand.

[george.burgess.iv]

Thanks!

llvm/trunk/include/llvm/Analysis/MemorySSA.h

public:
   }
 
   bool isOptimized() const {
     return getOptimized() && OptimizedID == getOptimized()->getID();
   }
 
   void resetOptimized() {
     OptimizedID = INVALID_MEMORYACCESS_ID;
+    setOperand(1, nullptr);
   }
 
   void print(raw_ostream &OS) const;
 
   unsigned getID() const { return ID; }
 
 private:
   static void deleteMe(DerivedUser *Self);