Revert "Speed up FxImporter by avoiding copying constants." (#4)

This reverts commit 2c5c287.

python/torch_mlir/extras/fx_importer.py

@@ -11,7 +11,6 @@
     # python less than 3.10 doesn't have NoneType
     NoneType = type(None)
 
-import ctypes
 import logging
 import operator
 import re
@@ -863,7 +862,7 @@ def import_frozen_program(
 
         # Lift buffers.
         for input_name, state_name in sig.inputs_to_buffers.items():
-            if hasattr(prog, 'constants') and state_name in prog.constants:
+            if hasattr(prog, "constants") and state_name in prog.constants:
                 state_value = prog.constants[state_name]
             else:
                 try:
@@ -2076,21 +2075,13 @@ def _make_vtensor_literal_op(
         assert (
             npy_dtype is not None
         ), f"Can not create literal tensor for unsupported datatype: {tensor.dtype}"
-
-        if tensor.is_contiguous():
-            cpu_tensor = tensor.cpu()
-            # If the tensor is contiguous and on CPU we can avoid the costly Tensor -> list -> numpy array below.
-            # Instead we can use ctypes to access the underlying bytes directly.
-            buffer_pointer = ctypes.cast(cpu_tensor.untyped_storage().data_ptr(), ctypes.POINTER(ctypes.c_char * cpu_tensor.untyped_storage().nbytes()))
-            np_tensor = np.frombuffer(bytes(buffer_pointer.contents), dtype=npy_dtype).reshape(cpu_tensor.shape)
-        else:
-            # We need a raw buffer of data in order to create an ElementsAttr for the invocation of torch.vtensor.literal,
-            # but torch.Tensor does not fulfill the python buffer/array interface hence we must convert to a numpy array to get
-            # a raw buffer of our data. We can't call torch.Tensor.numpy() directly because this internally forces a call to
-            # detach() which throws an error as we are operating in a FakeTensorMode, hence the simplest way to get this raw
-            # buffer is via the indirection: Tensor -> list -> numpy array. This allows us to create a vtensor literal as
-            # desired, but also limits which data types we can support in this function (see TORCH_DTYPE_TO_NPY_TYPE above)
-            np_tensor = np.array(tensor.tolist()).astype(npy_dtype)
+        # We need a raw buffer of data in order to create an ElementsAttr for the invocation of torch.vtensor.literal,
+        # but torch.Tensor does not fulfill the python buffer/array interface hence we must convert to a numpy array to get
+        # a raw buffer of our data. We can't call torch.Tensor.numpy() directly because this internally forces a call to
+        # detach() which throws an error as we are operating in a FakeTensorMode, hence the simplest way to get this raw
+        # buffer is via the indirection: Tensor -> list -> numpy array. This allows us to create a vtensor literal as
+        # desired, but also limits which data types we can support in this function (see TORCH_DTYPE_TO_NPY_TYPE above)
+        np_tensor = np.array(tensor.tolist()).astype(npy_dtype)
         # One element constants are more optimizable as splat DenseElementsAttr. DenseResourceElementsAttr does not
         # support splats, so don't use it for that case. In addition, at the time of writing, it has bugs with handling
         # 0d tensors.