fix some bug when merge sparse embedding parameters, test=develop (#18223)

1. fix the bug that out_put_var in SaveSelectedRows would be empty string
2. use merge_sparse_lookup_table to replace sum op for load_persistables_for_inference
3. fix the bug in _clone_var_in_block_ when the var is SELECTED_ROWS.

paddle/fluid/operators/save_op.h

@@ -102,16 +102,19 @@ class SaveOpKernel : public framework::OpKernel<T> {
   void SaveSelectedRows(const framework::ExecutionContext &ctx,
                         const platform::Place &place,
                         const framework::Variable *var) const {
-    framework::Variable *out_put_var = ctx.OutputVar(LOOKUP_TABLE_PATH);
-
     auto file_path = ctx.Attr<std::string>("file_path");
     auto overwrite = ctx.Attr<bool>("overwrite");
 
     std::string filename = file_path;
+    VLOG(4) << "SaveSelectedRows output file_path: " << file_path;
 
+    framework::Variable *out_put_var = ctx.scope().FindVar(LOOKUP_TABLE_PATH);
     if (out_put_var != nullptr) {
       auto *lt_var = out_put_var->GetMutable<std::string>();
-      filename = *lt_var;
+      if (lt_var->length() > 0) {
+        VLOG(4) << "SaveSelectedRows output var name: " << *lt_var;
+        filename = *lt_var;
+      }
     }
 
     if (FileExists(filename) && !overwrite) {

python/paddle/fluid/contrib/utils/lookup_table_utils.py

@@ -363,7 +363,17 @@ def load_persistables_for_inference(dirname, executor, program,
                 })
             sums.append(param_var)
         global_block.append_op(
-            type='sum', inputs={"X": sums}, outputs={'Out': emb_var}, attrs={})
+            type='merge_sparse_lookup_table',
+            inputs={"X": sums},
+            outputs={'Out': emb_var},
+            attrs={})
+        global_block.append_op(
+            type='save',
+            inputs={"X": [emb_var]},
+            outputs={},
+            attrs={
+                'file_path': os.path.join(lookup_table_dirname, emb_var.name)
+            })
         global_block.append_op(type='delete_var', inputs={'X': sums})
         executor.run(convert_program)
 

python/paddle/fluid/io.py

@@ -86,13 +86,21 @@ def is_persistable(var):
 
 def _clone_var_in_block_(block, var):
     assert isinstance(var, Variable)
-    return block.create_var(
-        name=var.name,
-        shape=var.shape,
-        dtype=var.dtype,
-        type=var.type,
-        lod_level=var.lod_level,
-        persistable=True)
+    if var.desc.type() == core.VarDesc.VarType.LOD_TENSOR:
+        return block.create_var(
+            name=var.name,
+            shape=var.shape,
+            dtype=var.dtype,
+            type=var.type,
+            lod_level=var.lod_level,
+            persistable=True)
+    else:
+        return block.create_var(
+            name=var.name,
+            shape=var.shape,
+            dtype=var.dtype,
+            type=var.type,
+            persistable=True)
 
 
 def save_vars(executor,