fix slice bug in while loop, test=develop (#24326)

python/paddle/fluid/framework.py

@@ -647,6 +647,7 @@ def _getitem_impl_(var, item):
     slice_step = []
     use_strided_slice = False
     reverse_axis = []
+    target_block = default_main_program().current_block()
 
     def fill_constant(shape, value, force_cpu=False, out=None):
         var.block.append_op(
@@ -701,8 +702,8 @@ def _getitem_impl_(var, item):
             if isinstance(slice_item, Variable):
                 temp_1 = var.block.create_var(dtype='int32')
                 fill_constant([1], 1, force_cpu=True, out=temp_1)
-                temp_end = var.block.create_var(dtype='int32')
-                var.block.append_op(
+                temp_end = target_block.create_var(dtype='int32')
+                target_block.append_op(
                     type='elementwise_add',
                     inputs={'X': slice_item,
                             'Y': temp_1},
@@ -785,11 +786,11 @@ def _getitem_impl_(var, item):
     out = var
     if use_strided_slice == False and len(slice_axis) > 0:
         # append slice_op here
-        slice_out_var = var.block.create_var(
+        slice_out_var = target_block.create_var(
             name=unique_name.generate_with_ignorable_key(var.name + "_slice"),
             dtype=var.dtype)
 
-        var.block.append_op(
+        target_block.append_op(
             type="slice",
             inputs=inputs,
             outputs={'Out': [slice_out_var]},
@@ -797,11 +798,11 @@ def _getitem_impl_(var, item):
 
         out = slice_out_var
     elif use_strided_slice == True and len(slice_axis) > 0:
-        strided_slice_out_var = var.block.create_var(
+        strided_slice_out_var = target_block.create_var(
             name=unique_name.generate_with_ignorable_key(var.name +
                                                          "_strided_slice"),
             dtype=var.dtype)
-        var.block.append_op(
+        target_block.append_op(
             type="strided_slice",
             inputs=inputs,
             outputs={'Out': [strided_slice_out_var]},
@@ -810,11 +811,11 @@ def _getitem_impl_(var, item):
         out = strided_slice_out_var
 
     if len(reverse_axis) > 0:
-        reverse_out_var = var.block.create_var(
+        reverse_out_var = target_block.create_var(
             name=unique_name.generate_with_ignorable_key(var.name +
                                                          "_slice_reverse"),
             dtype=var.dtype)
-        var.block.append_op(
+        target_block.append_op(
             type="reverse",
             inputs={'X': out},
             outputs={'Out': [reverse_out_var]},

python/paddle/fluid/tests/unittests/test_while_loop_op.py

@@ -494,5 +494,33 @@ class TestApiWhileLoop_Error(unittest.TestCase):
                               value_error_body_returns_with_mutable_list)
 
 
+class TestApiWhileLoopSliceInBody(unittest.TestCase):
+    def test_var_slice(self):
+        def cond(z, i):
+            return i + 1 <= x_shape[0]
+
+        def body(z, i):
+            z = z + x[i]
+            i += 1
+            return z, i
+
+        main_program = Program()
+        startup_program = Program()
+        with program_guard(main_program, startup_program):
+            x = fluid.layers.data(name='x', shape=[5], dtype='int32')
+            z = fluid.layers.fill_constant([1], 'int32', 0)
+            x_shape = fluid.layers.shape(x)
+            i = fluid.layers.fill_constant([1], 'int32', 0)
+            z, _ = fluid.layers.while_loop(cond, body, [z, i])
+
+        place = fluid.CUDAPlace(0) if core.is_compiled_with_cuda(
+        ) else fluid.CPUPlace()
+        exe = fluid.Executor(place)
+
+        np_x = np.array([1, 2, 3, 4, 5], dtype='int32')
+        res = exe.run(main_program, feed={'x': np_x}, fetch_list=[z])
+        self.assertTrue(np.array_equal(res[0], [np.sum(np_x)]))
+
+
 if __name__ == '__main__':
     unittest.main()