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The Function Dialect

The function dialect provides a set of statements to model semantics of Python-like functions, that means:

  • def <name>(<args>*, <kwargs>*) like function declarations
  • nested functions (namely closures)
  • high-order functions (functions can be used as arguments)
  • dynamically/statically calling a function or closure

func.Return

This is a simple statement that models the return statement in a function declaration. While this is a very simple statement, it is worth noting that this statement only accepts one argument of type ir.SSAValue because in Python (and most of other languages) functions always have a single return value, and multiple return values are represented by returning a tuple.

func.Function

This is the most fundamental statement that models a Python function.

Definition The func.Function takes no arguments, but contains a special str attribute (thus stored as PyAttr) that can be used as a symbolic reference within a symbol table. The func.Function also takes a func.Signature attribute to store the signature of corresponding function declaration. Last, it contains a ir.Region that represents the function body. The ir.Region follows the SSACFG convention where the blocks in the region forms a control flow graph.

Differences with MLIR

As Kirin's priority is writing eDSL as kernel functions in Python. To support high-order functions the entry block arguments always have their first argument self of type [types.MethodType][kirin.types.MethodType]. This is a design inspired by Julia's IR design.

As an example, the following Python function

from kirin.prelude import basic_no_opt

@basic_no_opt
def main(x):
    return x

will be lowered into the following IR, where main_self referencing the function itself.

func.func main(!Any) -> !Any {
  ^0(%main_self, %x):
  │ func.return %x
} // func.func main

the function can be terminated by a func.Return statement. All blocks in the function region must have terminators. In the lowering process, if the block is not terminated, a func.Return will be attached to return None in the function body. Thus func.Function can only have a single return value.

func.Call and func.Invoke

These two statements models the most common call convention in Python with consideration of compilation:

  • func.Call models dynamic calls where the callee is unknown at compile time, thus of type ir.SSAValue
  • func.Invoke models static calls where the callee is known at compile time, thus of type ir.Method

they both take inputs which is a tuple of ir.SSAValue as argument. Because we assume all functions will only return a single value, func.Call and func.Invoke only have a single result.

func.Lambda

This statement models nested functions (a.k.a closures). While most definitions are similar to func.Function the key difference is func.Lambda takes a tuple of ir.SSAValue arguments as captured. This models the captured variables for a nested function, e.g

the following Python function containing a closure inside with variable x being captured:

from kirin import basic_no_opt

@basic_no_opt
def main(x):
    def closure():
        return x
    return closure

will be lowered into

func.func main(!Any) -> !Any {
  ^0(%main_self, %x):
  │ %closure = func.lambda closure(%x) -> !Any {
  │            │ ^1(%closure_self):
  │            │ │ %x_1 = func.getfield(%closure_self, 0) : !Any
  │            │ │        func.return %x_1
  │            } // func.lambda closure
  │            func.return %closure
} // func.func main

Unlike func.Function this statement also has a result value which points to the closure itself. Inside the closure body, we insert func.GetField to unpack captured variables into the closure body.

API Reference

Call kirin-statement 

Call(
    callee: ir.SSAValue,
    inputs: tuple[ir.SSAValue, ...],
    *,
    kwargs: tuple[str, ...] = (),
    purity: bool
)

Bases: Statement

callee kirin-argument 

callee: SSAValue = argument()

inputs kirin-argument 

inputs: tuple[SSAValue, ...] = argument()

kwargs kirin-attribute kw-only 

kwargs: tuple[str, ...] = attribute(
    default_factory=lambda: ()
)

name class-attribute instance-attribute 

name = 'call'

purity kirin-attribute kw-only 

purity: bool = attribute(default=False)

result kirin-result 

result: ResultValue = result()

traits class-attribute instance-attribute 

traits = frozenset({MaybePure()})

check_type 

check_type() -> None

Check the types of the Block. Raises Exception if the types are not correct. This method is called by the verify_type method, which will detect the source of the error in the IR. One should always call the verify_type method to verify the types of the IR.

Note

This method is generated by the @statement decorator. But can be overridden if needed.

Source code in src/kirin/dialects/func/stmts.py 
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def check_type(self) -> None:
    if not self.callee.type.is_subseteq(types.MethodType):
        if self.callee.type.is_subseteq(types.PyClass(FunctionType)):
            raise ir.TypeCheckError(
                self,
                f"callee must be a method type, got {self.callee.type}",
                help="did you call a Python function directly? "
                "consider decorating it with kernel decorator",
            )

        if self.callee.type.is_subseteq(types.PyClass(ClassMethodType)):
            raise ir.TypeCheckError(
                self,
                "callee must be a method type, got class method",
                help="did you try to call a Python class method within a kernel? "
                "consider rewriting it with a captured variable instead of calling it inside the kernel",
            )

        if self.callee.type is types.Any:
            return
        raise ir.TypeCheckError(
            self,
            f"callee must be a method type, got {self.callee.type}",
            help="did you forget to decorate the function with kernel decorator?",
        )

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    pprint_calllike(self, printer.state.ssa_id[self.callee], printer)

ConstantNone kirin-statement 

ConstantNone()

Bases: Statement

A constant None value.

This is mainly used to represent the None return value of a function to match Python semantics.

name class-attribute instance-attribute 

name = 'const.none'

result kirin-result 

result: ResultValue = result(NoneType)

traits class-attribute instance-attribute 

traits = frozenset({Pure(), ConstantLike()})

FuncOpCallableInterface dataclass 

FuncOpCallableInterface()

Bases: CallableStmtInterface['Function']

get_callable_region classmethod 

get_callable_region(stmt: Function) -> ir.Region

Returns the body of the callable region

Source code in src/kirin/dialects/func/stmts.py 
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@classmethod
def get_callable_region(cls, stmt: "Function") -> ir.Region:
    return stmt.body

Function kirin-statement 

Function(
    *, sym_name: str, signature: Signature, body: ir.Region
)

Bases: Statement

body kirin-region kw-only 

body: Region = region(multi=True)

name class-attribute instance-attribute 

name = 'func'

signature kirin-attribute kw-only 

signature: Signature = attribute()

sym_name kirin-attribute kw-only 

sym_name: str = attribute()

The symbol name of the function.

traits class-attribute instance-attribute 

traits = frozenset(
    {
        IsolatedFromAbove(),
        SymbolOpInterface(),
        HasSignature(),
        FuncOpCallableInterface(),
        SSACFGRegion(),
    }
)

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    with printer.rich(style="keyword"):
        printer.print_name(self)
        printer.plain_print(" ")

    with printer.rich(style="symbol"):
        printer.plain_print(self.sym_name)

    printer.print_seq(self.signature.inputs, prefix="(", suffix=")", delim=", ")

    with printer.rich(style="comment"):
        printer.plain_print(" -> ")
        printer.print(self.signature.output)
        printer.plain_print(" ")

    printer.print(self.body)

    with printer.rich(style="comment"):
        printer.plain_print(f" // func.func {self.sym_name}")

GetField kirin-statement 

GetField(obj: ir.SSAValue, *, field: int)

Bases: Statement

field kirin-attribute kw-only 

field: int = attribute()

name class-attribute instance-attribute 

name = 'getfield'

obj kirin-argument 

obj: SSAValue = argument(MethodType)

result kirin-result 

result: ResultValue = result(init=False)

traits class-attribute instance-attribute 

traits = frozenset({Pure()})

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    printer.print_name(self)
    printer.plain_print(
        "(", printer.state.ssa_id[self.obj], ", ", str(self.field), ")"
    )
    with printer.rich(style="black"):
        printer.plain_print(" : ")
        printer.print(self.result.type)

Invoke kirin-statement 

Invoke(
    inputs: tuple[ir.SSAValue, ...],
    *,
    callee: ir.Method,
    kwargs: tuple[str, ...],
    purity: bool
)

Bases: Statement

callee kirin-attribute kw-only 

callee: Method = attribute()

inputs kirin-argument 

inputs: tuple[SSAValue, ...] = argument()

kwargs kirin-attribute kw-only 

kwargs: tuple[str, ...] = attribute()

name class-attribute instance-attribute 

name = 'invoke'

purity kirin-attribute kw-only 

purity: bool = attribute(default=False)

result kirin-result 

result: ResultValue = result()

traits class-attribute instance-attribute 

traits = frozenset({MaybePure()})

check 

check() -> None

Check the statement. Raises Exception if the statement is not correct. This method is called by the verify method, which will detect the source of the error in the IR. One should always call the verify method to verify the IR.

The difference between check and check_type is that check is called at any time to check the structure of the IR by verify, while check_type is called after the type inference to check the types of the IR.

Source code in src/kirin/dialects/func/stmts.py 
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def check(self) -> None:
    if self.kwargs:
        for name in self.kwargs:
            assert (
                name in self.callee.arg_names
            ), f"method {self.callee.sym_name} does not have argument {name}"
    elif len(self.callee.arg_names) - 1 != len(self.args):
        raise ValueError(
            f"expected {len(self.callee.arg_names)} arguments, got {len(self.args)}"
        )

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    pprint_calllike(self, self.callee.sym_name, printer)

Lambda kirin-statement 

Lambda(
    captured: tuple[ir.SSAValue, ...],
    *,
    sym_name: str,
    signature: Signature,
    body: ir.Region
)

Bases: Statement

body kirin-region kw-only 

body: Region = region(multi=True)

captured kirin-argument 

captured: tuple[SSAValue, ...] = argument()

name class-attribute instance-attribute 

name = 'lambda'

result kirin-result 

result: ResultValue = result(MethodType)

signature kirin-attribute kw-only 

signature: Signature = attribute()

sym_name kirin-attribute kw-only 

sym_name: str = attribute()

traits class-attribute instance-attribute 

traits = frozenset(
    {
        Pure(),
        HasSignature(),
        SymbolOpInterface(),
        FuncOpCallableInterface(),
        SSACFGRegion(),
    }
)

check 

check() -> None

Check the statement. Raises Exception if the statement is not correct. This method is called by the verify method, which will detect the source of the error in the IR. One should always call the verify method to verify the IR.

The difference between check and check_type is that check is called at any time to check the structure of the IR by verify, while check_type is called after the type inference to check the types of the IR.

Source code in src/kirin/dialects/func/stmts.py 
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def check(self) -> None:
    assert self.body.blocks, "lambda body must not be empty"

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    with printer.rich(style="keyword"):
        printer.print_name(self)
    printer.plain_print(" ")

    with printer.rich(style="symbol"):
        printer.plain_print(self.sym_name)

    printer.print_seq(self.captured, prefix="(", suffix=")", delim=", ")

    with printer.rich(style="bright_black"):
        printer.plain_print(" -> ")
        printer.print(self.signature.output)

    printer.plain_print(" ")
    printer.print(self.body)

    with printer.rich(style="black"):
        printer.plain_print(f" // func.lambda {self.sym_name}")

Return kirin-statement 

Return(
    value_or_stmt: ir.SSAValue | ir.Statement | None = None,
)

Bases: Statement

Source code in src/kirin/dialects/func/stmts.py 
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def __init__(self, value_or_stmt: ir.SSAValue | ir.Statement | None = None) -> None:
    if isinstance(value_or_stmt, ir.SSAValue):
        args = [value_or_stmt]
    elif isinstance(value_or_stmt, ir.Statement):
        if len(value_or_stmt._results) == 1:
            args = [value_or_stmt._results[0]]
        else:
            raise ValueError(
                f"expected a single result, got {len(value_or_stmt._results)} results from {value_or_stmt.name}"
            )
    elif value_or_stmt is None:
        args = []
    else:
        raise ValueError(f"expected SSAValue or Statement, got {value_or_stmt}")

    super().__init__(args=args, args_slice={"value": 0})

name class-attribute instance-attribute 

name = 'return'

traits class-attribute instance-attribute 

traits = frozenset({IsTerminator(), HasParent((Function,))})

value kirin-argument 

value: SSAValue = argument()

check 

check() -> None

Check the statement. Raises Exception if the statement is not correct. This method is called by the verify method, which will detect the source of the error in the IR. One should always call the verify method to verify the IR.

The difference between check and check_type is that check is called at any time to check the structure of the IR by verify, while check_type is called after the type inference to check the types of the IR.

Source code in src/kirin/dialects/func/stmts.py 
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def check(self) -> None:
    assert self.args, "return statement must have at least one value"
    assert len(self.args) <= 1, (
        "return statement must have at most one value"
        ", wrap multiple values in a tuple"
    )

print_impl 

print_impl(printer: Printer) -> None
Source code in src/kirin/dialects/func/stmts.py 
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def print_impl(self, printer: Printer) -> None:
    with printer.rich(style="keyword"):
        printer.print_name(self)

    if self.args:
        printer.plain_print(" ")
        printer.print_seq(self.args, delim=", ")