[NODEREF] Introduce named attribute system.

[tqchen]

So far we introduced Map<string, NodeRef> for general attribute storage. As we plan to upgrade the high-level IR, we would like to introduce more structure into it, specifically

• We would like to have something like dmlc::Parameter that declares the default value and attribute value property
• We also want to take benefit of the TVM's node system(directly access from python side).

This PR introduces attrs.h to solve the problem. The declaration API is relatively similar to dmlc::Parameter, and the Attrs is backed by the Node system. The general idea is that we declare the attribute in the C++, and it can be made accessible from the python side. We also introduce a DictAttrsNode that is backed by a dictionary, to mimic the python dict based object

Features

• Allow automatically set of default value when initialization value is not provided
• Provide bound checking and doc generation as in dmlc::Parameter
• Node system: field directly accessible from python side, serializable

C++ Declaration

struct TestAttrs : public AttrsNode<TestAttrs> {
  int axis;
  std::string name;
  Array<Expr> padding;
   TVM_DECLARE_ATTRS(TestAttrs, "attrs.TestAttrs") {
    TVM_ATTR_FIELD(axis)
        .set_default(10)
        .set_lower_bound(1)
        .set_upper_bound(10)
        .describe("axis field");
    TVM_ATTR_FIELD(name)
        .describe("name");
    TVM_ATTR_FIELD(padding)
        .describe("padding of input")
        .set_default(Array<Expr>({0, 0}));
  }
};

Python Side Access

def test_make_attrs():
     x = tvm.make.node("attrs.TestAttrs", name="xx", padding=(3,4))
    assert x.name == "xx"
    assert x.padding[0].value == 3
    assert x.padding[1].value == 4
    assert x.axis == 10
     
    dattr = tvm.make.node("DictAttrs", x=1, y=10, name="xyz", padding=(0,0))
    assert dattr.x.value == 1

[tqchen]

@jroesch @yzhliu @merrymercy please review

[jroesch]

Overall looks good to me, but we sat together and talked design and implementation, maybe good to get review from others?

[jroesch]

This module enables declaration named attributes

should be:

This module enables declaration of named attributes

[jroesch]

and support default value setup and bound checking.

should be:

which support default value setup and bound checking.

[jroesch]

The type key to be used by the TVM node system.

[jroesch]

Error thrown during attribute checking.

[jroesch]

Why do we store the type in string format? is this the string key?

[tqchen]

This is used in docstring, clarified in the comment

[jroesch]

The english here is unclear.

Namespace containing detail implementations?

[jroesch]

Nit: Could we make these full sentences ?

[jroesch]

Could you explain this more in depth?

[jroesch]

This is grammatically strange, maybe The corresponding DLS node.?

[jroesch]

Is this to make the attributes more flexible?

[tqchen]

Yes, for example, user can do add_one(x, 1), and in the backend we can directly fetch out a float, for functions that want to do so

[tqchen]

@jroesch review comments address, please take another look

[jroesch]

👍

[tqchen]

Thanks @jroesch this is now merged