[PYTHON] Improve equal sugar (#564)

* [PYTHON] Improve equal sugar

* fix comment

python/tvm/expr.py

@@ -16,7 +16,7 @@ For example, you can use addexp.a to get the left operand of an Add node.
 """
 # pylint: disable=missing-docstring
 from __future__ import absolute_import as _abs
-from ._ffi.node import NodeBase, register_node
+from ._ffi.node import NodeBase, NodeGeneric, register_node
 from . import make as _make
 from . import _api_internal
 
@@ -89,10 +89,10 @@ class ExprOp(object):
         return _make.LE(self, other)
 
     def __eq__(self, other):
-        return self.equal(other)
+        return EqualOp(self, other)
 
     def __ne__(self, other):
-        return _make.NE(self, other)
+        return NotEqualOp(self, other)
 
     def __gt__(self, other):
         return _make.GT(self, other)
@@ -138,12 +138,71 @@ class ExprOp(object):
         return _make.static_cast(dtype, self)
 
 
+class EqualOp(NodeGeneric, ExprOp):
+    """Deferred equal operator.
+
+    This is used to support sugar that a == b can either
+    mean NodeBase.same_as or NodeBase.equal.
+
+    Parameters
+    ----------
+    a : Expr
+        Left operand.
+
+    b : Expr
+        Right operand.
+    """
+    def __init__(self, a, b):
+        self.a = a
+        self.b = b
+
+    def __nonzero__(self):
+        return self.a.same_as(self.b)
+
+    def __bool__(self):
+        return self.__nonzero__()
+
+    def asnode(self):
+        """Convert node."""
+        return _make.EQ(self.a, self.b)
+
+
+class NotEqualOp(NodeGeneric, ExprOp):
+    """Deferred NE operator.
+
+    This is used to support sugar that a != b can either
+    mean not NodeBase.same_as or make.NE.
+
+    Parameters
+    ----------
+    a : Expr
+        Left operand.
+
+    b : Expr
+        Right operand.
+    """
+    def __init__(self, a, b):
+        self.a = a
+        self.b = b
+
+    def __nonzero__(self):
+        return not self.a.same_as(self.b)
+
+    def __bool__(self):
+        return self.__nonzero__()
+
+    def asnode(self):
+        """Convert node."""
+        return _make.NE(self.a, self.b)
+
+
 class Expr(ExprOp, NodeBase):
     """Base class of all tvm Expressions"""
     # In Python3, We have to explicity tell interpreter to retain __hash__ if we overide __eq__
     # https://docs.python.org/3.1/reference/datamodel.html#object.__hash__
     __hash__ = NodeBase.__hash__
 
+
 class ConstExpr(Expr):
     pass
 
@@ -215,19 +274,11 @@ class Max(BinaryOpExpr):
 
 @register_node
 class EQ(CmpExpr):
-    def __nonzero__(self):
-        return self.a.same_as(self.b)
-
-    def __bool__(self):
-        return self.__nonzero__()
+    pass
 
 @register_node
 class NE(CmpExpr):
-    def __nonzero__(self):
-        return not self.a.same_as(self.b)
-
-    def __bool__(self):
-        return self.__nonzero__()
+    pass
 
 @register_node
 class LT(CmpExpr):

tests/python/unittest/test_ir_builder.py

@@ -31,6 +31,7 @@ def test_if():
             A[0] = A[i] + 2
 
     body = ib.get()
+    assert A == A
     assert isinstance(body, tvm.stmt.For)
     body = body.body
     assert isinstance(body, tvm.stmt.IfThenElse)
@@ -42,6 +43,7 @@ def test_prefetch():
     A = tvm.placeholder((10, 20), name="A")
     ib = tvm.ir_builder.create()
     n = tvm.var("n")
+
     with ib.for_range(0, n, name="i") as i:
         ib.emit(
             tvm.make.Prefetch(