What is the best way to match against optional attributes?

[xuzhenqi]

Suppose we need to remove an optional input of a node, for example, we want to replace DFT(x, None, -2) with DFT(x), since the default axis is -2, so we can remove the axis input.

The DFT node has two optional attributes (onesided and inverse). What is the best way to write pattern to cover these cases:

• DFT(x, None, -2) -> DFT(x)
• DFT(x, None, -2, onesided=1) -> DFT(x, onesided=1)
• DFT(x, None, -2, inverse=1) -> DFT(x, inverse=1)
• DFT(x, None, -2, inverse=1, onesided=1) -> DFT(x, inverse=1, onesided=1)

It seems we need write four rules for the four cases, is there any better solutions? cc @justinchuby

[xuzhenqi]

https://github.com/microsoft/onnxscript/blob/main/onnxscript/rewriter/pattern.py#L534

What if we allow an attr pattern to bind a None value?

[justinchuby]

@gramalingam