fix(mge/imperative): fix tensor astype failed for quantized type

GitOrigin-RevId: 383458acbf18fa956ca1ccaa376255ff1b06735a

imperative/python/megengine/core/tensor/dtype.py

@@ -62,6 +62,21 @@ def get_zero_point(dtype):
     return metadata["zero_point"]
 
 
+def is_equal(dt0, dt1):
+    def _get_zero_point(dtype):
+        assert is_quantize(dtype)
+        metadata = dtype.metadata["mgb_dtype"]
+        return metadata.get("zero_point")
+
+    if is_quantize(dt0) and is_quantize(dt1):
+        return get_scale(dt0) == get_scale(dt1) and _get_zero_point(
+            dt0
+        ) == _get_zero_point(dt1)
+    if not (is_quantize(dt0) or is_quantize(dt1)):
+        return dt0 == dt1
+    return False
+
+
 def _check_zero_point(zp: int, dtype_str: str):
     qmin = _metadata_dict[dtype_str].qmin
     qmax = _metadata_dict[dtype_str].qmax

imperative/python/megengine/core/tensor/utils.py

@@ -14,6 +14,7 @@ import numpy as np
 from ..ops import builtin
 from ..ops.special import Const
 from ..tensor.core import OpBase, TensorBase, TensorWrapperBase, apply
+from .dtype import is_equal
 
 
 def dtype_promotion(inputs):
@@ -112,7 +113,7 @@ def concatenate(inputs, axis=0, *, device=None):
 
 def astype(x, dtype):
     dtype = np.dtype(dtype)
-    if x.dtype != dtype:
+    if not is_equal(x.dtype, dtype):
         (x,) = apply(builtin.TypeCvt(param=dtype), x)
     return x
 

imperative/python/test/unit/core/test_tensor_wrapper.py

@@ -8,6 +8,7 @@
 # "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 import numpy as np
 
+from megengine.core.tensor.dtype import get_scale, get_zero_point, qint8, quint8
 from megengine.core.tensor.tensor_wrapper import TensorWrapper
 
 
@@ -71,3 +72,17 @@ def test_transpose():
     x = np.random.rand(2, 5).astype("float32")
     xx = TensorWrapper(x)
     np.testing.assert_almost_equal(xx.T.numpy(), x.T)
+
+
+def test_as_type():
+    x = TensorWrapper([1, 2, 3], dtype=np.float32)
+    y = x.astype(qint8(0.1))
+    np.testing.assert_almost_equal(get_scale(y.dtype), 0.1)
+    z = y.astype(qint8(0.2))
+    np.testing.assert_almost_equal(get_scale(z.dtype), 0.2)
+    a = z.astype(quint8(0.3, 127))
+    np.testing.assert_almost_equal(get_scale(a.dtype), 0.3)
+    np.testing.assert_equal(get_zero_point(a.dtype), 127)
+    b = a.astype(quint8(0.3, 128))
+    np.testing.assert_almost_equal(get_scale(b.dtype), 0.3)
+    np.testing.assert_equal(get_zero_point(b.dtype), 128)