[PYTHON] Improve equal sugar

[tqchen]

A followup of #550 The make.EQ will raise an error when the operands handle type. So we defer that in python instead cc @wweic

[wweic]

I'd like to understand what errors you are seeing.

One case I see not covered is bool(EqualOp == EqualOp), it will fail since EqualOp does not have same_as(inherited from NodeBase).

In [1]: import tvm

In [2]: a = tvm.const(1)

In [3]: type(a)
Out[3]: tvm.expr.IntImm

In [4]: b = a == a

In [5]: type(b)
Out[5]: tvm.expr.EqualOp

In [6]: bool(b) # works since a has same_as as it's IntImm
Out[6]: True

In [7]: c = b == b # now let's compare EqualOp

In [8]: type(c)
Out[8]: tvm.expr.EqualOp

In [9]: bool(c) # fails since EqualOp does not have same_as
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-9-f5dcfc4a672a> in <module>()
----> 1 bool(c) # fails since EqualOp does not have same_as

/Users/weichen/workspace/deep-learning/tvm/python/tvm/expr.py in __bool__(self)
    161
    162     def __bool__(self):
--> 163         return self.__nonzero__()
    164
    165     def asnode(self):

/Users/weichen/workspace/deep-learning/tvm/python/tvm/expr.py in __nonzero__(self)
    158
    159     def __nonzero__(self):
--> 160         return self.a.same_as(self.b)
    161
    162     def __bool__(self):

AttributeError: 'EqualOp' object has no attribute 'same_as'

[tqchen]

The original error is caused because HalideIR prevents comparison among handle types. So an error will be raised when we do

x = tvm.var("x", "handle")
y = (x==x)

[wweic]

I'm not able to reproduce the error you pasted by reverting your commit in my local branch. But with #567, I think == should work as we expect most of the time.