Remove internal executorch dependency on torchao.quantization.subclass (pytorch#15223)

Summary:

**Summary:** This is a really old quantization API that we
recently removed in torchao (D84842047). No one should be
calling it anymore. For BC, let's just copy the base class
into executorch for now. We should delete this in the future.

**Test Plan:** CI

bypass-github-export-checks

Reviewed By: vkuzo

Differential Revision: D84921134

Author: andrewor14

examples/models/llama/experimental/__init__.py

@@ -26,7 +26,8 @@
 from executorch.extension.gguf_util.load_gguf import GGUFWeights, load_file
 from gguf import ReaderTensor
 from gguf.constants import GGMLQuantizationType
-from torchao.quantization.subclass import QuantizedLinearWeightBase
+
+from .subclass import QuantizedLinearWeightBase
 
 FORMAT = "[%(levelname)s %(asctime)s %(filename)s:%(lineno)s] %(message)s"
 logging.basicConfig(level=logging.INFO, format=FORMAT)

examples/models/llama/experimental/load_gguf_q4_0.py

@@ -20,7 +20,12 @@
 #
 # This layout is handled internally in the tensor subclass.
 import torch
-from torchao.quantization.subclass import QuantizedLinearWeightBase
+
+from executorch.exir._warnings import deprecated
+from torch.utils._python_dispatch import return_and_correct_aliasing
+
+
+aten = torch.ops.aten
 
 
 def down_size(size):
@@ -129,6 +134,173 @@ def to_float(
     return a * scale.unsqueeze(1)
 
 
+@deprecated("QuantizedLinearWeightBase is deleted from torchao. DO NOT USE!")
+class QuantizedLinearWeightBase(torch.Tensor):
+    """
+    *** LEGACY TORCHAO TENSOR SUBCLASS ***
+
+    Note: this subclass no longer exists in torchao. No one should be importing or extending this
+    subclass anymore. It is added back here just for internal executorch BC. DO NOT USE!
+
+    Base quantized tensor subclass for quantized linear weights. When the from_float method is used,
+    to create an instance of any QuantizedLinearWeightBase, we assume the input
+    weight is oriented the way it is in a normal linear op, i.e. out-channels x in-channels.
+
+    The shape and dtype of the tensor subclass represent how the tensor subclass looks externally,
+    regardless of the internal representation's type or orientation.
+    """
+
+    @staticmethod
+    def __new__(cls, int_data, transposed, shape, *args, **kwargs):
+        kwargs["device"] = int_data.device
+        kwargs["layout"] = (
+            kwargs.get("layout") if kwargs.get("layout", False) else int_data.layout
+        )
+        assert "dtype" in kwargs
+        assert not kwargs.get("requires_grad", False)
+        kwargs["requires_grad"] = False
+        return torch.Tensor._make_wrapper_subclass(cls, shape, **kwargs)  # type: ignore[attr-defined]
+
+    def __init__(self, int_data, transposed, *args, **kwargs):
+        self.int_data = int_data
+
+        self.transposed = transposed
+
+    @staticmethod
+    def _quantized_op(act_mat, w_qtensor, bias):
+        pass
+
+    def __repr__(self):
+        return (
+            f"{self.__class__.__name__}(data={self.dequantize()}, shape={self.shape}, "
+            f"device={self.device}, dtype={self.dtype}, requires_grad={self.requires_grad})"
+        )
+
+    def dequantize(self):
+        pass
+
+    def int_repr(self):
+        pass
+
+    def q_params(self):
+        pass
+
+    def half(self):
+        return self.to(torch.float16)
+
+    def _get_to_kwargs(self, *args, **kwargs):
+        device, dtype, _, memory_format = torch._C._nn._parse_to(*args, **kwargs)
+        device = self.device if device is None else device
+        dtype = self.dtype if dtype is None else dtype
+        memory_format = (
+            memory_format if memory_format is not None else torch.preserve_format
+        )
+        kwargs = {
+            "device": device,
+            "dtype": dtype,
+            "memory_format": memory_format,
+        }
+        return kwargs
+
+    def _apply_fn_to_data(self, fn):
+        pass
+
+    def _change_shape(self):
+        pass
+
+    def __tensor_flatten__(self):
+        pass
+
+    @classmethod
+    def __tensor_unflatten__(
+        cls, tensor_data_dict, tensor_attributes, outer_size, outer_stride
+    ):
+        pass
+
+    @classmethod
+    def from_float(cls, input_float):
+        pass
+
+    # __torch_function__ = torch._C._disabled_torch_function_impl
+
+    @classmethod
+    def __torch_function__(cls, func, types, args=(), kwargs=None):
+        kwargs = {} if kwargs is None else kwargs
+
+        if func is torch.nn.functional.linear:
+            mat1, w_qtensor, bias = (
+                args[0],
+                args[1],
+                args[2] if len(args) > 2 else None,
+            )
+            assert not w_qtensor.transposed
+            return cls._quantized_op(mat1, w_qtensor, bias)
+
+        try:
+            with torch._C.DisableTorchFunctionSubclass():
+                return func(*args, **kwargs)
+        except Exception:
+            print(f"ERR: subclass doesn't implement {func}")
+
+    @classmethod
+    def __torch_dispatch__(cls, func, types, args, kwargs):
+        # two scenarios where we currently fall back to vanilla mm:
+        # 1 - when tensor is on CPU: we are missing qmm for CPU, but we should have a CPU implementation
+        #     for consistency and to allow people to test
+        # 2 - we're given non-floats - quantizing long to int8 is crazy
+        if (
+            func in [aten.mm.default, aten.addmm.default]
+            and args[0].is_floating_point()
+            and args[0].is_cuda
+        ):
+            if func == aten.addmm.default:
+                assert args[1].shape[-1] == args[2].shape[0], (
+                    f"need mat1 shape: {args[1].shape} final"
+                    f"dim to match mat2 shape: {args[2].shape} first dim "
+                )
+                mat1, w_qtensor, bias = (
+                    args[1],
+                    args[2],
+                    args[0],
+                )
+            else:
+                assert args[0].shape[-1] == args[1].shape[0], (
+                    f"need mat1 shape: {args[0].shape} final dim"
+                    f"to match mat2 shape: {args[1].shape} first dim"
+                )
+                mat1, w_qtensor, bias = (
+                    args[0],
+                    args[1],
+                    None if len(args) == 2 else args[2],
+                )
+            # call the quantized op for the specific type
+            # of quantized tensor subclass
+            return cls._quantized_op(mat1, w_qtensor, bias)
+
+        if func is aten.detach.default:
+            return return_and_correct_aliasing(
+                func, args, kwargs, args[0]._apply_fn_to_data(torch.detach)
+            )
+
+        if func is aten.clone.default:
+            return return_and_correct_aliasing(
+                func, args, kwargs, args[0]._apply_fn_to_data(torch.clone)
+            )
+
+        if func is aten.t.default:
+            args[0].transposed = not args[0].transposed
+            new = args[0]._change_shape(args[0].shape[::-1])
+            return return_and_correct_aliasing(func, args, kwargs, new)
+
+        if func is aten._to_copy.default:
+            return return_and_correct_aliasing(
+                func,
+                args,
+                kwargs,
+                args[0].to(*args[1:], **kwargs)._apply_fn_to_data(torch.clone),
+            )
+
+
 class GGMLInt4LinearWeight(QuantizedLinearWeightBase):
     """
     A Tensor subclass that when applied to a weight used in a linear op/module,