[Question] TypesMatchWith fails to verify type match

MLIR
1

Hello everyone!
I’m currently implementing a dataflow-centered dialect. For that, I have an input type that represents the input end of a FIFO channel. An associated op is used to push items into the channel:

dfg.push(%value) %chan : (i32) -> !dfg.input<i32>

Since I want to ensure type correctness here, I want to model the constraint that the type of %value matches the inner type of %chan. So, I thought (after browsing the MLIR codebase and seeing this post) I can use TypesMatchWith for my purposes.

I implemented dfg.push like this:

def Dfg_PushOp : Dfg_Op<
    "push",
    [
        TypesMatchWith<"Channel type matches pushed type",
                       "chan", "inp",
                       "InputType::get($_ctxt, $_self).getElementType()">
    ]
> {
    // -- snip --
    let arguments = (ins AnyType: $inp, Dfg_InputType: $chan);
    let assemblyFormat = [{
        `(` $inp `)` $chan attr-dict `:` functional-type($inp, $chan)
    }];
}

def Dfg_InputType : Dfg_Type<"Input", []> {
    let mnemonic = "input";
    // -- snip --
    let parameters = (ins "Type":$elementType);
    let assemblyFormat = "`<` $elementType `>`";
}

However, a (in my opinion) correct code sample like the one above triggers the verification failure “failed to verify that Channel type matches pushed type”. Am I using TypesMatchWith incorrectly (which I assume) or is there a bug?

Thanks in advance for any hints!

2 
// A type constraint that denotes `transform(lhs.getType()) == rhs.getType()`.
// An optional comparator function may be provided that changes the above form
// into: `comparator(transform(lhs.getType()), rhs.getType())`.
class TypesMatchWith<string summary, string lhsArg, string rhsArg,
                     string transform, string comparator = "std::equal_to<>()">

lhs here is chan, but chan is the input type, so I’d expect inp to be the one transformed with what you have there.

3

But isn’t that exactly what you’d want to do? I put chan on the lhs to then use the InputType::getElementType() getter and retrieve the type enclosed in the input, which should then be equal to the rhs.

4

Okay, I got it sorted out now. The issue indeed was here:

InputType::get is the wrong approach in this case. Instead, what you want is this:

$_self.cast<InputType>().getElementType()