add more logs and comments

test=develop

Author: panyx0718

paddle/fluid/framework/details/op_handle_base.h

@@ -31,6 +31,7 @@ constexpr char kLocalExecScopeName[] = "@LCOAL_SCOPE@";
 // It's responsible for populating necessary fields of ir::Node.
 class OpHandleBase {
  public:
+  // Owned by `node`. No need to be deleted explicitly.
   explicit OpHandleBase(ir::Node *node) : node_(node) {
     node_->WrappedBy(this);
   }

paddle/fluid/framework/details/var_handle.cc

@@ -20,13 +20,19 @@ namespace details {
 
 VarHandleBase::~VarHandleBase() {}
 
+VarHandle::~VarHandle() { VLOG(4) << "deleting var handle " << DebugString(); }
+
 std::string VarHandle::DebugString() const {
   std::stringstream ss;
   ss << name_ << ":" << place_;
   return ss.str();
 }
 
 std::string DummyVarHandle::DebugString() const { return node_->Name(); }
+
+DummyVarHandle::~DummyVarHandle() {
+  VLOG(4) << "deleting dummy var handle " << DebugString();
+}
 }  // namespace details
 }  // namespace framework
 }  // namespace paddle

paddle/fluid/framework/details/var_handle.h

@@ -35,6 +35,7 @@ class OpHandleBase;
 // A variable can only be generated by a single operator. i.e.
 // This is a single assignment graph.
 struct VarHandleBase {
+  // Owned by `node`. No need to be deleted explicitly.
   explicit VarHandleBase(ir::Node* node) : node_(node) {
     node_->WrappedBy(this);
   }
@@ -96,6 +97,8 @@ struct VarHandleBase {
 struct VarHandle : public VarHandleBase {
   explicit VarHandle(ir::Node* node) : VarHandleBase(node) {}
 
+  virtual ~VarHandle();
+
   std::string DebugString() const override;
 
   VarHandle(ir::Node* node, size_t version, size_t scope_index,
@@ -123,6 +126,8 @@ struct VarHandle : public VarHandleBase {
 struct DummyVarHandle : public VarHandleBase {
   explicit DummyVarHandle(ir::Node* node) : VarHandleBase(node) {}
 
+  virtual ~DummyVarHandle();
+
   std::string DebugString() const override;
 };
 

paddle/fluid/framework/ir/node.h

@@ -49,6 +49,7 @@ class Node {
  public:
   virtual ~Node() {
     if (!wrapper_.empty()) {
+      VLOG(4) << "ir::Node deleting a wrapper node " << Name();
       wrapper_deleter_();
     }
   }