Improve #449: Improve StridedMemoryView creation time

Two changes:

1. Refactor the versioned/non-versioned paths to reduce the number of branches.
2. Create shape and strides tuples using Python/C API

Author: mdboom

cuda_core/cuda/core/experimental/_memoryview.pyx

@@ -184,48 +184,52 @@ cdef StridedMemoryView view_as_dlpack(obj, stream_ptr, view=None):
             stream=int(stream_ptr) if stream_ptr else None)
 
     cdef void* data = NULL
+    cdef DLTensor* dl_tensor
+    cdef DLManagedTensorVersioned* dlm_tensor_ver
+    cdef DLManagedTensor* dlm_tensor
+    cdef const char *used_name
     if cpython.PyCapsule_IsValid(
             capsule, DLPACK_VERSIONED_TENSOR_UNUSED_NAME):
         data = cpython.PyCapsule_GetPointer(
             capsule, DLPACK_VERSIONED_TENSOR_UNUSED_NAME)
         versioned = True
+        dlm_tensor_ver = <DLManagedTensorVersioned*>data
+        dl_tensor = &dlm_tensor_ver.dl_tensor
+        is_readonly = bool((dlm_tensor_ver.flags & DLPACK_FLAG_BITMASK_READ_ONLY) != 0)
+        used_name = DLPACK_VERSIONED_TENSOR_USED_NAME
     elif cpython.PyCapsule_IsValid(
             capsule, DLPACK_TENSOR_UNUSED_NAME):
         data = cpython.PyCapsule_GetPointer(
             capsule, DLPACK_TENSOR_UNUSED_NAME)
         versioned = False
-    else:
-        assert False
-
-    cdef DLManagedTensor* dlm_tensor
-    cdef DLManagedTensorVersioned* dlm_tensor_ver
-    cdef DLTensor* dl_tensor
-    if versioned:
-        dlm_tensor_ver = <DLManagedTensorVersioned*>data
-        dl_tensor = &dlm_tensor_ver.dl_tensor
-        is_readonly = bool((dlm_tensor_ver.flags & DLPACK_FLAG_BITMASK_READ_ONLY) != 0)
-    else:
         dlm_tensor = <DLManagedTensor*>data
         dl_tensor = &dlm_tensor.dl_tensor
         is_readonly = False
+        used_name = DLPACK_TENSOR_USED_NAME
+    else:
+        assert False
 
     cdef StridedMemoryView buf = StridedMemoryView() if view is None else view
     buf.ptr = <intptr_t>(dl_tensor.data)
-    buf.shape = tuple(int(dl_tensor.shape[i]) for i in range(dl_tensor.ndim))
+    
+    # Construct shape and strides tuples using the Python/C API for speed
+    buf.shape = cpython.PyTuple_New(dl_tensor.ndim)
+    for i in range(dl_tensor.ndim):
+        cpython.PyTuple_SET_ITEM(buf.shape, i, cpython.PyLong_FromLong(dl_tensor.shape[i]))
     if dl_tensor.strides:
-        buf.strides = tuple(
-            int(dl_tensor.strides[i]) for i in range(dl_tensor.ndim))
+        buf.strides = cpython.PyTuple_New(dl_tensor.ndim)
+        for i in range(dl_tensor.ndim):
+            cpython.PyTuple_SET_ITEM(buf.strides, i, cpython.PyLong_FromLong(dl_tensor.strides[i]))
     else:
         # C-order
         buf.strides = None
+
     buf.dtype = dtype_dlpack_to_numpy(&dl_tensor.dtype)
     buf.device_id = device_id
     buf.is_device_accessible = is_device_accessible
     buf.readonly = is_readonly
     buf.exporting_obj = obj
 
-    cdef const char* used_name = (
-        DLPACK_VERSIONED_TENSOR_USED_NAME if versioned else DLPACK_TENSOR_USED_NAME)
     cpython.PyCapsule_SetName(capsule, used_name)
 
     return buf
@@ -308,8 +312,10 @@ cdef StridedMemoryView view_as_cai(obj, stream_ptr, view=None):
     buf.dtype = numpy.dtype(cai_data["typestr"])
     buf.strides = cai_data.get("strides")
     if buf.strides is not None:
-        # convert to counts
-        buf.strides = tuple(s // buf.dtype.itemsize for s in buf.strides)
+        # convert to counts, using the Python/C API for speed
+        for i in range(len(buf.strides)):
+            cpython.PyTuple_SET_ITEM(buf.strides, i,
+                cpython.PyLong_FromLong(buf.strides[i] // buf.dtype.itemsize))
     buf.is_device_accessible = True
     buf.device_id = handle_return(
         driver.cuPointerGetAttribute(