Revert regression in Reshape c-impl speed

This was caused by 223ee15, which used the generic `PyArray_IntpConverter` to convert the shape numpy vector into a simple C-array for the Reshape operation. There seems to be no justification for this change.

Author: ricardoV94

pytensor/tensor/shape.py

@@ -16,7 +16,6 @@
 from pytensor.link.c.op import COp
 from pytensor.link.c.params_type import ParamsType
 from pytensor.npy_2_compat import normalize_axis_tuple
-from pytensor.scalar import int32
 from pytensor.tensor import _get_vector_length, as_tensor_variable, get_vector_length
 from pytensor.tensor import basic as ptb
 from pytensor.tensor.elemwise import get_normalized_batch_axes
@@ -628,14 +627,11 @@ class Reshape(COp):
 
     check_input = False
     __props__ = ("ndim",)
-    params_type = ParamsType(ndim=int32)
-    # name does not participate because it doesn't affect computations
 
-    def __init__(self, ndim, name=None):
+    def __init__(self, ndim):
         self.ndim = int(ndim)
         if ndim < 0:
             raise ValueError("The output dimensions after reshape must be 0 or greater")
-        assert name is None, "name attribute for Reshape has been deprecated"
 
     def __str__(self):
         return f"{self.__class__.__name__}{{{self.ndim}}}"
@@ -795,33 +791,32 @@ def infer_shape(self, fgraph, node, ishapes):
             ]
 
     def c_code_cache_version(self):
-        return (9,)
+        return (10,)
 
     def c_code(self, node, name, inputs, outputs, sub):
         x, shp = inputs
+        shp_dtype = node.inputs[1].type.dtype_specs()[1]
         (z,) = outputs
         fail = sub["fail"]
-        params = sub["params"]
+        ndim = self.ndim
+
         return f"""
         assert (PyArray_NDIM({shp}) == 1);
 
-        PyArray_Dims newshape;
-
-        if (!PyArray_IntpConverter((PyObject *){shp}, &newshape)) {{
-            {fail};
+        // Unpack shape into new_dims
+        npy_intp new_dims[{ndim}];
+        for (int ii = 0; ii < {ndim}; ++ii)
+        {{
+            new_dims[ii] = (({shp_dtype}*)(PyArray_DATA({shp}) + ii * PyArray_STRIDES({shp})[0]))[0];
         }}
 
-        if ({params}->ndim != newshape.len) {{
-            PyErr_SetString(PyExc_ValueError, "Shape argument to Reshape has incorrect length");
-            PyDimMem_FREE(newshape.ptr);
-            {fail};
-        }}
+        PyArray_Dims newshape;
+        newshape.len = {ndim};
+        newshape.ptr = new_dims;
 
         Py_XDECREF({z});
         {z} = (PyArrayObject *) PyArray_Newshape({x}, &newshape, NPY_CORDER);
 
-        PyDimMem_FREE(newshape.ptr);
-
         if (!{z}) {{
             //The error message should have been set by PyArray_Newshape
             {fail};

tests/tensor/test_shape.py

@@ -858,3 +858,14 @@ def test_unbroadcast(self):
         node = unbroadcast(mat, 0).owner
         vect_node = vectorize_node(node, tns)
         assert equal_computations(vect_node.outputs, [unbroadcast(tns, 2)])
+
+
+def test_reshape_benchmark(benchmark):
+    x = tensor3("x")
+    x_val = np.random.random((2, 3, 4)).astype(config.floatX)
+
+    y = x.reshape((6, 4))
+    reshape_fn = pytensor.function([x], y)
+
+    reshape_fn.trust_input = True
+    benchmark(reshape_fn, x_val)