除法转乘法

代码实现见 tvm/src/relay/transforms/div_to_mul.cc，使用如下：

import tvm
from tvm import relay
import numpy as np

for dtype, rtol in [("float16", 1e-3), ("float32", 1e-7), ("float64", 1e-12)]:
    x = relay.var("x", relay.TensorType((), dtype))
    y = relay.Constant(tvm.nd.array(np.array([1.5]).astype(dtype)))
    z = x / y
    mod = tvm.IRModule.from_expr(z)
    transformed = relay.transform.DivToMul()(mod)
    assert transformed["main"].body.op.name == "multiply"
    np.testing.assert_allclose(transformed["main"].body.args[1].data.numpy()[0], 1 / 1.5, rtol=rtol)