Fix Parallel Exe(VarHandel's version)

Author: chengduoZH

paddle/fluid/framework/details/multi_devices_graph_builder.cc

@@ -345,7 +345,7 @@ void MultiDevSSAGraphBuilder::InsertAllReduceOp(SSAGraph *result,
     auto &prev_grad = vars.back();
     op_handle->AddInput(prev_grad.get());
 
-    auto var = new VarHandle(vars.size() - 1, i, og, p);
+    auto var = new VarHandle(vars.size(), i, og, p);
     vars.emplace_back(var);
     op_handle->AddOutput(var);
   }
@@ -442,8 +442,7 @@ VarHandle *MultiDevSSAGraphBuilder::CreateReduceOp(SSAGraph *result,
     op_handle->AddInput(prev_grad.get());
   }
   auto &vars = result->vars_[dst_dev_id][og];
-  auto var =
-      new VarHandle(vars.size() - 1, dst_dev_id, og, places_[dst_dev_id]);
+  auto var = new VarHandle(vars.size(), dst_dev_id, og, places_[dst_dev_id]);
   vars.emplace_back(var);
   op_handle->AddOutput(var);
   return var;