IRDLOperation definition failed when more than one optional operand

[ice-tong]

Thank so much for the xDSL project! xDSL has made it much easier for people to start developing MLIR, which is a really great achievement!

When I was looking into xDSL development recently, I had a problem when I tried to define operations with more than two optional operands, which caused unexpected errors. I'm not sure if this is what was expected.

Below is a small piece of code that shows the problem:

from xdsl.dialects.builtin import *
from xdsl.ir import *
from xdsl.irdl import *

@irdl_op_definition
class TestOp(IRDLOperation):
    name = "test.op"

    input1 = opt_operand_def(AnyAttr())
    input2 = opt_operand_def(AnyAttr())

    output = result_def(AnyAttr())

We got the following error message. We might be treating the optional operand like the variadic operand when we check multiple variadic operands.

❯ python test_opt_operand_def.py
Traceback (most recent call last):
  File "/xxx/test_opt_operand_def.py", line 7, in <module>
    class TestOp(IRDLOperation):
  File "/xxx/xdsl/irdl/operations.py", line 2048, in irdl_op_definition
    new_attrs = get_accessors_from_op_def(op_def, getattr(cls, "verify_", None))
  File "/xxx/xdsl/xdsl/irdl/operations.py", line 1959, in get_accessors_from_op_def
    irdl_op_arg_definition(new_attrs, VarIRConstruct.OPERAND, op_def)
  File "/xxx/xdsl/irdl/operations.py", line 1891, in irdl_op_arg_definition
    raise PyRDLOpDefinitionError(
xdsl.utils.exceptions.PyRDLOpDefinitionError: Operation test.op defines more than two variadic operands, but do not define any of SameVariadicOperandSize or AttrSizedOperandSegments PyRDL options.

[superlopuh]

We should probably make this happen automatically, but all you need is this:

        irdl_options = [AttrSizedOperandSegments()]

The error message mentions this but could be clearer.

I'm glad you're finding it useful!

[ice-tong]

Hi @superlopuh, thank you very much for your prompt response!

The method you provided does work for me!

However, I encountered the problem after using xdsl-tblgen to automatically generate the PyRDL from the TableGen file. It would be helpful if this issue could be resolved automatically~

[superlopuh]

@math-fehr, do you think we should fix xdsl-tblgen or remove the need for the irdl_options?

[ice-tong]

Hi @superlopuh @math-fehr,

I hope you don't mind me sharing my thoughts on this topic. I'm not entirely sure if I'm correct, but I believe it makes sense to check for multiple Variadic operand/result variables. However, I feel that Optional being a subclass of Variadic might not be the most appropriate.

For reference, according to the ONNX IR spec:

• Optional indicates that it can be omitted (for an optional operand, a placeholder can be used instead).
• Variadic signifies that there are at least N variables, and it must be the last operand or result variable.

[superlopuh]

We followed MLIR here, and it makes sense for Optional to be a subclass of Variadic in this case, as it's effectively a subrange of operands that can be length 0 or 1, whereas Variadic can be length 0, 1, 2, and so on.

[ice-tong]

@superlopuh Thank you very much for your reply and correcting my opinions. It sounds fine！

[math-fehr]

I'll try to implement that this week, shouldn't be that hard to add support for it in xdsl-tblgen!