made perform and c_code of join work in place and added test for it

theano/tensor/basic.py

@@ -3888,10 +3888,12 @@ class Join(Op):
     check_input = False
     __props__ = ("view",)
 
-    def __init__(self, view=False):
+    def __init__(self, view=-1):
         self.view = view
-        if view:
-            self.view_map = {0: [0]}
+        if view != -1:
+            # since the first input is always the axis, the tensors
+            # start from index 1.
+            self.view_map = {0: [1 + view]}
 
     def make_node(self, *axis_and_tensors):
         """
@@ -4003,12 +4005,13 @@ class Join(Op):
 
     def perform(self, node, axis_and_tensors, out_):
         out, = out_
+        view = self.view
         axis, tensors = axis_and_tensors[0], axis_and_tensors[1:]
-        # tailing tensors are all tensors except the first one
-        tailing_tensors_are_empty = numpy.all(
-            [tensor.shape[axis] == 0 for tensor in axis_and_tensors[2:]])
-        if tailing_tensors_are_empty:
-            out[0] = tensors[0]
+        # we check these tensors for being empty.
+        if (view != -1) and numpy.all(
+                [tensor.shape[axis] == 0 for tensor in
+                 tensors[0:view] + tensors[view + 1:]]):
+            out[0] = tensors[view]
 
         else:
             ndim = tensors[0].ndim
@@ -4020,18 +4023,32 @@ class Join(Op):
                                      dtype=node.outputs[0].type.dtype)
 
     def c_code_cache_version(self):
-        return
-        return (3,)
+        return (4,)
 
-    def c_code_(self, node, name, inputs, outputs, sub):
+    def c_code(self, node, name, inputs, outputs, sub):
         axis, tensors = inputs[0], inputs[1:]
+        view = self.view
+        non_empty_tensor = tensors[view]
         input_1 = tensors[0]
         l = len(tensors)
         out, = outputs
         fail = sub['fail']
         adtype = node.inputs[0].type.dtype_specs()[1]
         code = """
-        PyObject* list = PyList_New(%(l)s);
+        int axis = ((%(adtype)s *)PyArray_DATA(%(axis)s))[0];
+        int tensors_lens_sum = 0""" % locals()
+        for i, inp in enumerate(tensors):
+            code += """ + PyArray_DIM(%(inp)s, axis) """ % locals()
+        code += """;\n
+        tensors_lens_sum -= PyArray_DIM(%(non_empty_tensor)s, axis);
+
+        if(%(view)s != -1 && tensors_lens_sum == 0){
+            Py_XDECREF(%(out)s);
+            Py_INCREF(%(non_empty_tensor)s);
+            %(out)s = %(non_empty_tensor)s;
+        }
+        else{
+            PyObject* list = PyList_New(%(l)s);
         """ % locals()
         for i, inp in enumerate(tensors):
             code += """
@@ -4039,21 +4056,19 @@ class Join(Op):
             PyList_SetItem(list, %(i)s, (PyObject*)%(inp)s);
             """ % locals()
         code += """
-        //PyObject* PyArray_Concatenate(PyObject* obj, int axis)
-        int axis = ((%(adtype)s *)PyArray_DATA(%(axis)s))[0];
-        int ndim = PyArray_NDIM(%(input_1)s);
-        if( axis < -ndim ){
-            PyErr_Format(PyExc_IndexError,
-                         "Join axis %%d out of bounds [0, %%d)", axis, ndim);
-            %(fail)s
-        }
-
-        Py_XDECREF(%(out)s);
-        %(out)s = (PyArrayObject *)PyArray_Concatenate(list, axis);
-
-        Py_DECREF(list);
-        if(!%(out)s){
-            %(fail)s
+            //PyObject* PyArray_Concatenate(PyObject* obj, int axis)
+            int ndim = PyArray_NDIM(%(input_1)s);
+            if( axis < -ndim ){
+                PyErr_Format(PyExc_IndexError,
+                             "Join axis %%d out of bounds [0, %%d)", axis, ndim);
+                %(fail)s
+            }
+            Py_XDECREF(%(out)s);
+            %(out)s = (PyArrayObject *)PyArray_Concatenate(list, axis);
+             (list);
+            if(!%(out)s){
+                %(fail)s
+            }
         }
         """ % locals()
         return code

theano/tensor/tests/test_basic.py

@@ -4251,6 +4251,29 @@ class T_Join_and_Split(unittest.TestCase):
                     for node in f.maker.fgraph.toposort()])
         self.assertRaises(ValueError, f)
 
+def test_join_inplace():
+    """Test join to work inplace.
+
+    This function tests the case when several elements are passed to the
+    join function but all except one of them are empty. In this case join
+    should work inplace and the output should be the view of the non-empty
+    element.
+    """
+    s = tensor.lscalar()
+    x = tensor.vector('x')
+    z = tensor.zeros((s,))
+
+    join = Join(view=0)
+    c = join(0, x, z, z)
+
+    f = theano.function([theano.In(x, borrow=True), s], theano.Out(c, borrow=True))
+
+    data = numpy.array([3, 4, 5], dtype=theano.config.floatX)
+    print (f(data, 0))
+
+    assert f(data, 0) is data
+    assert numpy.allclose(f(data, 0), [3, 4, 5])
+
 
 class test_comparison(unittest.TestCase):
     """Test <, >, <=, >=, == and !=