expr.const函数，用于根据指定的值创建一个Constant类。
    注意，value可以是bool, int, float, numpy.ndarray, tvm.nd.NDArray
    python/tvm/relay/expr.py

    1. def const(value, dtype=None):
    2.     """Create a constant value.
    4.     Parameters
    5.     ----------
    6.     value: Union[bool, int, float, numpy.ndarray, tvm.nd.NDArray]
    7.         The constant value.
    9.     dtype: str, optional
    10.         The data type of the value.
    12.     Note
    13.     ----
    14.     When dtype is None, we use the following rule:
    16.     - int maps to "int32"
    17.     - float maps to "float32"
    18.     - bool maps to "bool"
    19.     - other using the same default rule as numpy.
    20.     """
    21.     if isinstance(value, (_base.numeric_types, (bool, list))):
    22.         value = _np.array(value, dtype=dtype)
    24.     if not dtype:
    25.         # when dtype is None: int maps to "int32", float maps to "float32"
    26.         map_dtype = {
    27.             _np.dtype('int64'): _np.int32,
    28.             _np.dtype('float64'): _np.float32
    29.             }.get(value.dtype, None)
    30.         if map_dtype:
    31.             value = value.astype(map_dtype)
    33.     if isinstance(value, (_np.ndarray, _np.generic)):
    34.         value = _nd.array(value)
    36.     if not isinstance(value, _nd.NDArray):
    37.         raise ValueError("value has to be scalar or NDArray")
    38.     return Constant(value)

    该函数有一个bug, 如果value是_np.ndarray 或_np.generic类型，提供的dtype是无效的。如果要指定dtype，需要先将value.astype(dtype)。