sz_w() of expanded function doesn't match codegen

[ghorn]

I'm code-generating a function. I'm checking that the work vector size sz_w() in python matches the code-generated sz_w. I noticed that when the function is expanded with Function::expand(), sz_w matches the unexpanded function, but the code-generated expanded function does not match.

Reproduction on casadi 3.6.4:

"""Reproduction for inconsistent sz_w."""

from pathlib import Path

import casadi


def test_casadi_function_generation() -> None:
    """Compare sz_w between python and codegen, for MX and expanded function."""
    x = casadi.MX.sym("x", 2)
    y = casadi.MX.sym("y")
    function = casadi.Function("f", [x, y], [x, casadi.sin(y) * x], ["x", "y"], ["r", "q"])

    # test the nominal function
    print("")
    print(f"function.sz_arg(): {function.sz_arg()}")
    print(f"function.sz_res(): {function.sz_res()}")
    print(f"function.sz_iw(): {function.sz_iw()}")
    print(f"function.sz_w(): {function.sz_w()}")
    assert function.sz_arg() == 4  # this passes
    assert function.sz_res() == 3  # this passes
    assert function.sz_iw() == 0   # this passes
    assert function.sz_w() == 3    # this passes

    # generate file
    filename1 = "gen1.c"
    function.generate(filename1)

    # open and print file
    with Path(filename1).open() as handle:
        lines = handle.readlines()
        line_index = _get_work_fun_line(lines)
        print("".join(lines[line_index : line_index + 7]))  # codegen consistent with above assertions

    # test the expanded function
    expanded_function = function.expand()
    print(f"expanded_function.sz_arg(): {expanded_function.sz_arg()}")
    print(f"expanded_function.sz_res(): {expanded_function.sz_res()}")
    print(f"expanded_function.sz_iw(): {expanded_function.sz_iw()}")
    print(f"expanded_function.sz_w(): {expanded_function.sz_w()}")
    assert expanded_function.sz_arg() == 2  # this passes
    assert expanded_function.sz_res() == 2  # this passes
    assert expanded_function.sz_iw() == 0   # this passes
    assert expanded_function.sz_w() == 3    # PASSES BUT IS INCONSISTENT WITH CODEGEN

    # generate file
    filename2 = "gen2.c"
    expanded_function.generate(filename2)

    # open and print file
    with Path(filename2).open() as handle:
        lines = handle.readlines()
        line_index = _get_work_fun_line(lines)
        print("".join(lines[line_index : line_index + 7]))  # codegen says sz_w == 0


def _get_work_fun_line(lines):
    """Get the line number that starts the work function."""
    start = (
        "CASADI_SYMBOL_EXPORT int f_work(casadi_int *sz_arg, casadi_int* sz_res, casadi_int *sz_iw, casadi_int *sz_w)"
    )
    for k, line in enumerate(lines):
        if start in line:
            return k
    err_msg = f"could not find '{start}' in file"
    raise ValueError(err_msg)

if __name__ == '__main__':
    test_casadi_function_generation()

Here are the results

function.sz_arg(): 4
function.sz_res(): 3
function.sz_iw(): 0
function.sz_w(): 3
CASADI_SYMBOL_EXPORT int f_work(casadi_int *sz_arg, casadi_int* sz_res, casadi_int *sz_iw, casadi_int *sz_w) {
  if (sz_arg) *sz_arg = 4;
  if (sz_res) *sz_res = 3;
  if (sz_iw) *sz_iw = 0;
  if (sz_w) *sz_w = 3;
  return 0;
}

expanded_function.sz_arg(): 2
expanded_function.sz_res(): 2
expanded_function.sz_iw(): 0
expanded_function.sz_w(): 3
CASADI_SYMBOL_EXPORT int f_work(casadi_int *sz_arg, casadi_int* sz_res, casadi_int *sz_iw, casadi_int *sz_w) {
  if (sz_arg) *sz_arg = 2;
  if (sz_res) *sz_res = 2;
  if (sz_iw) *sz_iw = 0;
  if (sz_w) *sz_w = 0;
  return 0;
}

notice that for the code generated function, sz_w is 0 but in python it's reported as 3

[jaeandersson]

When evaluated in codegen, local variables will be allocated instead of using the work vector. So the work vector isn't needed for SX codegen. So it's not really a problem.

[jaeandersson]

Closing as I think that this is expected behavior

[ghorn]

Thank you!