[Dy2Stat]Remove unnecessary vars from gast.comprehension in LoopTransformer. (#25094)

python/paddle/fluid/dygraph/dygraph_to_static/loop_transformer.py

@@ -117,15 +117,16 @@ class NameVisitor(gast.NodeVisitor):
                 var_node.ctx)
 
         in_loop_vars = set(in_loop_vars_list)
+        in_loop_vars = self._remove_unnecessary_vars(in_loop_vars, node)
         in_loop_name_strs = self._var_nodes_to_names(in_loop_vars)
 
         before_loop_body_vars = self.before_loop_body_vars[node]
-        before_loop_body_vars = self._remove_target_vars_of_for(
+        before_loop_body_vars = self._remove_unnecessary_vars(
             before_loop_body_vars, node)
         before_loop_name_strs = self._var_nodes_to_names(before_loop_body_vars)
 
         after_loop_vars = self.current_seen_vars - before_loop_body_vars - in_loop_vars
-        after_loop_vars = self._remove_target_vars_of_for(after_loop_vars, node)
+        after_loop_vars = self._remove_unnecessary_vars(after_loop_vars, node)
         after_loop_name_strs = self._var_nodes_to_names(after_loop_vars,
                                                         read_context)
         condition_vars = self.condition_vars[node]
@@ -138,7 +139,6 @@ class NameVisitor(gast.NodeVisitor):
         for var in in_loop_vars:
             wrapper = self.node_to_wrapper_map[var]
             name_to_type[self._var_node_to_name(var)] = wrapper.node_var_type
-
         for name in in_loop_name_strs:
             if name in before_loop_name_strs:
                 # If a variable is used in loop and created before loop
@@ -296,47 +296,83 @@ class NameVisitor(gast.NodeVisitor):
             return parent_node
         return None
 
-    def _remove_target_vars_of_for(self, before_or_after_loop_vars, loop_node):
+    def _remove_unnecessary_vars(self, loop_vars, loop_node):
         """
-        Remove target vars of gast.For from before_loop_vars or after_loop_vars.
-        :param before_or_after_loop_vars: before_loop_vars or after_loop_vars of loop_node.
+        Remove unnecessary vars from before_loop_vars, after_loop_vars or in_loop_vars about loop_node.
+            1. Remove target vars of gast.For from before_loop_vars or after_loop_vars.
+            2. Remove vars only in gast.comprehension.
+        :param loop_vars: before_loop_vars, after_loop_vars or in_loop_vars of loop_node.
         :param loop_node: Current loop node.
         """
 
-        removed_vars = set()
-        for name_node in before_or_after_loop_vars:
+        vars_of_list_generator = set()
+        target_vars_of_for_node = set()
+
+        for name_node in loop_vars:
             if not isinstance(name_node, gast.Name):
                 continue
 
             parent_node = self._get_parent_node(name_node)
 
-            # NOTE: gast.For.target can be gast.Tuple.
-            #  For example: `for i, j in enumerate(x)` has two target vars: i and j
+            # NOTE: gast.For.target or gast.comprehension.target can be gast.Tuple.
+            #  For examples:
+            #   1) `for i, j in enumerate(x)` has two target vars: i and j
+            #   2) `[x for x,y in array]` has two target vars: x and y
             if isinstance(parent_node, gast.Tuple):
                 parent_node = self._get_parent_node(parent_node)
 
-            if isinstance(parent_node,
-                          gast.For) and parent_node is not loop_node:
+            # 1. Get vars only in gast.comprehension.
+            # For examples:
+            #  1) [x for x,y in array] -> x, x, y
+            #  2) [f(x) for x in array] -> x
+            #  3) [func(x, y) for x in array] -> x, x
+            if isinstance(parent_node, gast.comprehension):
+                # 1.1 target vars in list/set comprehensions
                 target_node = parent_node.target
-
                 if isinstance(target_node, gast.Tuple):
                     target_vars = target_node.elts
                 else:
                     target_vars = [target_node]
 
-                if name_node in target_vars:
-                    removed_vars.add(name_node)
+                vars_of_list_generator = vars_of_list_generator | set(
+                    target_vars)
+
+                # 1.2 vars from target vars used in elt_node
+                target_var_names = {var.id for var in target_vars}
+                listcomp_node = self._get_parent_node(parent_node)
+                elt_node = listcomp_node.elt
+                if isinstance(elt_node, gast.Name):
+                    if elt_node.id in target_var_names:
+                        vars_of_list_generator.add(elt_node)
+                for child_node in gast.walk(elt_node):
+                    if isinstance(child_node, gast.Name):
+                        if child_node.id in target_var_names:
+                            vars_of_list_generator.add(child_node)
+
+            # 2. Get target vars or vars from target vars used in for-loop.
+            elif isinstance(parent_node,
+                            gast.For) and parent_node is not loop_node:
+                # 2.1 target vars in gast.For node.
+                target_node = parent_node.target
+                if isinstance(target_node, gast.Tuple):
+                    target_vars = target_node.elts
+                else:
+                    target_vars = [target_node]
 
-        removed_vars_name_strs = {var.id for var in removed_vars}
+                target_vars_of_for_node = target_vars_of_for_node | set(
+                    target_vars)
 
-        for var in before_or_after_loop_vars:
+        # 2.2 vars from target vars used in for-loop
+        target_vars_name_strs = {var.id for var in target_vars_of_for_node}
+        for var in loop_vars:
             if not isinstance(var, gast.Name):
                 continue
-            if var.id in removed_vars_name_strs and var not in self.condition_vars[
+            if var.id in target_vars_name_strs and var not in self.condition_vars[
                     loop_node]:
-                removed_vars.add(var)
+                target_vars_of_for_node.add(var)
 
-        return before_or_after_loop_vars - removed_vars
+        removed_vars = target_vars_of_for_node | vars_of_list_generator
+        return loop_vars - removed_vars
 
 
 class LoopTransformer(gast.NodeTransformer):

python/paddle/fluid/tests/unittests/dygraph_to_static/test_loop.py

@@ -169,15 +169,28 @@ def nested_for_loop_dyfunc():
     return b
 
 
+def for_loop_dufunc_with_listcomp(array):
+    a = 1
+    for j in range(array):
+        res = [x + a for x in array]
+        res = [i for i in array]
+        x = 1
+    b = [i for i in array]
+    print(x)
+    return res
+
+
 class TestNameVisitor(unittest.TestCase):
     def setUp(self):
         self.loop_funcs = [
-            while_loop_dyfunc, for_loop_dyfunc, while_loop_dyfunc_with_none
+            while_loop_dyfunc, for_loop_dyfunc, while_loop_dyfunc_with_none,
+            for_loop_dufunc_with_listcomp
         ]
         self.loop_var_names = [
-            set(["i", "x"]), set(["i", "ret", "max_len"]), set(["i", "x"])
+            set(["i", "x"]), set(["i", "ret", "max_len"]), set(["i", "x"]),
+            set(["j", "array", "res", "x"])
         ]
-        self.create_var_names = [set(), set(["ret"]), set()]
+        self.create_var_names = [set(), set(["ret"]), set(), set(["res", "x"])]
 
         self.nested_for_loop_func = nested_for_loop_dyfunc
 
@@ -211,7 +224,6 @@ class TestNameVisitor(unittest.TestCase):
             if isinstance(node, (gast.While, gast.For)):
                 loop_var_names, create_var_names = name_visitor.get_loop_var_names(
                     node)
-                # print(loop_var_names)
                 self.assertEqual(loop_var_names, self.loop_var_names[i])
                 self.assertEqual(create_var_names, self.create_var_names[i])
                 i += 1