8324969: C2: prevent elimination of unbalanced coarsened locking regions

src/hotspot/share/opto/compile.cpp

@@ -4868,10 +4868,21 @@ void Compile::add_coarsened_locks(GrowableArray<AbstractLockNode*>& locks) {
   if (length > 0) {
     // Have to keep this list until locks elimination during Macro nodes elimination.
     Lock_List* locks_list = new (comp_arena()) Lock_List(comp_arena(), length);
+#ifdef ASSERT
+    AbstractLockNode* alock = locks.at(0);
+    BoxLockNode* box = alock->box_node()->as_BoxLock();
+#endif
     for (int i = 0; i < length; i++) {
       AbstractLockNode* lock = locks.at(i);
       assert(lock->is_coarsened(), "expecting only coarsened AbstractLock nodes, but got '%s'[%d] node", lock->Name(), lock->_idx);
       locks_list->push(lock);
+#ifdef ASSERT
+      BoxLockNode* this_box = lock->box_node()->as_BoxLock();
+      if (this_box != box) {
+        this_box->mark_unbalanced();
+        box->mark_unbalanced();
+      }
+#endif
     }
     _coarsened_locks.append(locks_list);
   }
@@ -4974,8 +4985,10 @@ void Compile::mark_unbalanced_boxes() {
           if (box != this_box) {
             box->set_unbalanced();
             this_box->set_unbalanced();
+            assert(this_box->is_marked_unbalanced(),"inconsistency");
           }
         }
+        assert(box->is_unbalanced() == box->is_marked_unbalanced(),"inconsistency");
       }
     }
   }

src/hotspot/share/opto/locknode.cpp

@@ -41,6 +41,7 @@ uint BoxLockNode::size_of() const { return sizeof(*this); }
 
 BoxLockNode::BoxLockNode( int slot ) : Node( Compile::current()->root() ),
                                        _slot(slot), _kind(BoxLockNode::Regular) {
+  DEBUG_ONLY(_marked_unbalanced = false);
   init_class_id(Class_BoxLock);
   init_flags(Flag_rematerialize);
   OptoReg::Name reg = OptoReg::stack2reg(_slot);

src/hotspot/share/opto/locknode.hpp

@@ -42,6 +42,9 @@ class BoxLockNode : public Node {
     Eliminated         // All lock/unlock in region were eliminated
   } _kind;
 
+  // In debug VM verify correctness of unbalanced marking
+  DEBUG_ONLY(bool _marked_unbalanced;)
+
 public:
   BoxLockNode( int lock );
   virtual int Opcode() const;
@@ -67,6 +70,11 @@ class BoxLockNode : public Node {
   void set_eliminated()      { _kind = Eliminated; }
   void set_unbalanced()      { _kind = Unbalanced; }
 
+#ifdef ASSERT
+  void mark_unbalanced()            { _marked_unbalanced = true; }
+  bool is_marked_unbalanced() const { return _marked_unbalanced; }
+#endif
+
   // Is BoxLock node used for one simple lock region?
   bool is_simple_lock_region(LockNode** unique_lock, Node* obj, Node** bad_lock);