GTFN CPU bindings cannot handle tuples

[samkellerhals]

Field operators which return a tuple fail using the gtfn cpu backend:

Example field operators:

@field_operator
    def _unpack(
            inp: Field[[IDim], float64],
    ) -> tuple[
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
    ]:
        a, b, c, d = (inp + 2., inp + 3., inp + 5., inp + 7.)
        return a, b, c, d

@field_operator
    def _unpack(
            inp: Field[[IDim], float64],
    ) -> tuple[
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64],
        Field[[IDim], float64]
    ]:
        *a, a2, a3 = (inp, inp + 2., inp + 3., inp + 5.)
        b1, *b, b3 = (inp + 7., inp + 11., inp + 13., inp + 17.)
        c1, c2, *c = (inp + 19., inp + 23., inp + 29., inp + 31.)

        a_sum = a[0] + a[1]
        b_sum = b[0] + b[1]
        c_sum = c[0] + c[1]

        return a_sum, a2, a3, b1, b_sum, b3, c1, c2, c_sum

The following error occurs in the generated bindings:

/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/./common_interface.hpp:25:47: error: no matching function for call to ‘get<-1>(gridtools::tuple<double, double, double, double>)’
In file included from /tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/common/iterate_on_host_device.hpp:72,
                 from /tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/backend/../../common/tuple_util.hpp:478,
                 from /tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/backend/../../common/hymap.hpp:106,
                 from /tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/backend/naive.hpp:13,
                 from /tmp/gt4py_cache/unpack_6cab28797b68484a541fc8abd58bcde586a1740d683737077b524e4d4321005a/unpack.cpp.inc:1,
                 from /tmp/gt4py_cache/unpack_6cab28797b68484a541fc8abd58bcde586a1740d683737077b524e4d4321005a/unpack_bindings.cpp:1:
/tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/common/tuple_util.hpp:518:64: note: candidate: ‘template<long unsigned int I, class T, class Getter> constexpr decltype(auto) gridtools::tuple_util::host::get(T&&)’
  518 |             GT_TARGET GT_FORCE_INLINE constexpr decltype(auto) get(T && obj) noexcept {
      |                                                                ^~~
/tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/common/tuple_util.hpp:518:64: note:   template argument deduction/substitution failed:
In file included from /tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/cartesian.hpp:16,
                 from /tmp/gt4py_cache/unpack_6cab28797b68484a541fc8abd58bcde586a1740d683737077b524e4d4321005a/unpack.cpp.inc:4,
                 from /tmp/gt4py_cache/unpack_6cab28797b68484a541fc8abd58bcde586a1740d683737077b524e4d4321005a/unpack_bindings.cpp:1:
/tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include/gridtools/fn/./common_interface.hpp:25:47: error: narrowing conversion of ‘-1’ from ‘int’ to ‘long unsigned int’ [-Wnarrowing]
   25 |         return tuple_util::host_device::get<I>(std::forward<Tuple>(t));
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/c++ -DBOOST_ALL_NO_LIB -Dunpack_EXPORTS -I/tmp/gt4py_cache/compile_commands_cache_gridtools_master_pybind11_2_9_2_Debug__7d6131381ac7c32e4f8dc19a1bccf7c68e5d21953a0fdafeb68f42bea07c5c45/build/_deps/gridtools-src/include -isystem /home/sk/Dev/gt4py/.venv/lib/python3.10/site-packages/pybind11/include -isystem /usr/include/python3.10 -g -fPIC -MD -MT build/unpack_bindings.cpp.o -MF build/unpack_bindings.cpp.o.d -o build/unpack_bindings.cpp.o -c /tmp/gt4py_cache/unpack_6cab28797b68484a541fc8abd58bcde586a1740d683737077b524e4d4321005a/unpack_bindings.cpp

[havogt]

Creating the bindings for tuples is part of this cycle (if we don't need the resources for one of the more urgent projects).

[havogt]

done