feat[next]: Index builtin

src/gt4py/next/iterator/builtins.py

@@ -22,6 +22,11 @@ def as_fieldop(*args):
     raise BackendNotSelectedError()
 
 
+@builtin_dispatch
+def index(*args):
+    raise BackendNotSelectedError()
+
+
 @builtin_dispatch
 def deref(*args):
     raise BackendNotSelectedError()
@@ -430,6 +435,7 @@ def bool(*args):  # noqa: A001 [builtin-variable-shadowing]
     "unstructured_domain",
     "named_range",
     "as_fieldop",
+    "index",
     *MATH_BUILTINS,
 }
 

src/gt4py/next/iterator/embedded.py

@@ -1156,6 +1156,7 @@ def ndarray(self) -> core_defs.NDArrayObject:
     def asnumpy(self) -> np.ndarray:
         raise NotImplementedError()
 
+    # TODO(tehrengruber): Use a regular zero dimensional field instead.
     def as_scalar(self) -> core_defs.IntegralScalar:
         if self.domain.ndim != 0:
             raise ValueError(
@@ -1174,12 +1175,13 @@ def premap(
 
     def restrict(self, item: common.AnyIndexSpec) -> Self:
         if isinstance(item, Sequence) and all(isinstance(e, common.NamedIndex) for e in item):
+            assert len(item) == 1
             assert isinstance(item[0], common.NamedIndex)  # for mypy errors on multiple lines below
             d, r = item[0]
             assert d == self._dimension
             assert isinstance(r, core_defs.INTEGRAL_TYPES)
             return self.__class__(self._dimension, r)
-        # TODO set a domain...
+        # TODO: set a domain...
         raise NotImplementedError()
 
     __call__ = premap
@@ -1701,6 +1703,11 @@ def impl(*args):
     return impl
 
 
+@builtins.index.register(EMBEDDED)
+def index(axis: common.Dimension) -> common.Field:
+    return IndexField(axis)
+
+
 @runtime.closure.register(EMBEDDED)
 def closure(
     domain_: Domain,

src/gt4py/next/iterator/ir.py

@@ -101,13 +101,18 @@ class StencilClosure(Node):
     domain: FunCall
     stencil: Expr
     output: Union[SymRef, FunCall]
-    inputs: List[SymRef]
+    inputs: List[Union[SymRef, FunCall]]
 
     @datamodels.validator("output")
     def _output_validator(self: datamodels.DataModelTP, attribute: datamodels.Attribute, value):
         if isinstance(value, FunCall) and value.fun != SymRef(id="make_tuple"):
             raise ValueError("Only FunCall to 'make_tuple' allowed.")
 
+    @datamodels.validator("inputs")
+    def _input_validator(self: datamodels.DataModelTP, attribute: datamodels.Attribute, value):
+        if any(isinstance(v, FunCall) and v.fun != SymRef(id="index") for v in value):
+            raise ValueError("Only FunCall to 'index' allowed.")
+
 
 UNARY_MATH_NUMBER_BUILTINS = {"abs"}
 UNARY_LOGICAL_BUILTINS = {"not_"}
@@ -183,6 +188,7 @@ def _output_validator(self: datamodels.DataModelTP, attribute: datamodels.Attrib
     "can_deref",
     "scan",
     "if_",
+    "index",  # `index(dim)` creates a dim-field that has the current index at each point
     *ARITHMETIC_BUILTINS,
     *TYPEBUILTINS,
 }

src/gt4py/next/iterator/pretty_parser.py

@@ -31,9 +31,9 @@
     INT_LITERAL: SIGNED_INT
     FLOAT_LITERAL: SIGNED_FLOAT
     OFFSET_LITERAL: ( INT_LITERAL | CNAME ) "ₒ"
-    _literal: INT_LITERAL | FLOAT_LITERAL | OFFSET_LITERAL
+    AXIS_LITERAL: CNAME ("ᵥ" | "ₕ")
+    _literal: INT_LITERAL | FLOAT_LITERAL | OFFSET_LITERAL | AXIS_LITERAL
     ID_NAME: CNAME
-    AXIS_NAME: CNAME ("ᵥ" | "ₕ")
 
     ?prec0: prec1
         | "λ(" ( SYM "," )* SYM? ")" "→" prec0 -> lam
@@ -84,7 +84,7 @@
     else_branch_seperator: "else"
     if_stmt: "if" "(" prec0 ")" "{" ( stmt )* "}" else_branch_seperator "{" ( stmt )* "}"
 
-    named_range: AXIS_NAME ":" "[" prec0 "," prec0 ")"
+    named_range: AXIS_LITERAL ":" "[" prec0 "," prec0 ")"
     function_definition: ID_NAME "=" "λ(" ( SYM "," )* SYM? ")" "→" prec0 ";"
     declaration: ID_NAME "=" "temporary(" "domain=" prec0 "," "dtype=" TYPE_LITERAL ")" ";"
     stencil_closure: prec0 "←" "(" prec0 ")" "(" ( SYM_REF ", " )* SYM_REF ")" "@" prec0 ";"
@@ -128,7 +128,7 @@ def OFFSET_LITERAL(self, value: lark_lexer.Token) -> ir.OffsetLiteral:
     def ID_NAME(self, value: lark_lexer.Token) -> str:
         return value.value
 
-    def AXIS_NAME(self, value: lark_lexer.Token) -> ir.AxisLiteral:
+    def AXIS_LITERAL(self, value: lark_lexer.Token) -> ir.AxisLiteral:
         name = value.value[:-1]
         kind = ir.DimensionKind.HORIZONTAL if value.value[-1] == "ₕ" else ir.DimensionKind.VERTICAL
         return ir.AxisLiteral(value=name, kind=kind)

src/gt4py/next/iterator/type_system/type_synthesizer.py

@@ -189,6 +189,14 @@ def make_tuple(*args: ts.DataType) -> ts.TupleType:
     return ts.TupleType(types=list(args))
 
 
+@_register_builtin_type_synthesizer
+def index(arg: ts.DimensionType) -> ts.FieldType:
+    return ts.FieldType(
+        dims=[arg.dim],
+        dtype=ts.ScalarType(kind=getattr(ts.ScalarKind, itir.INTEGER_INDEX_BUILTIN.upper())),
+    )
+
+
 @_register_builtin_type_synthesizer
 def neighbors(offset_literal: it_ts.OffsetLiteralType, it: it_ts.IteratorType) -> it_ts.ListType:
     assert (

src/gt4py/next/program_processors/codegens/gtfn/codegen.py

@@ -260,6 +260,17 @@ def visit_Program(self, node: gtfn_ir.Program, **kwargs: Any) -> Union[str, Coll
     #include <gridtools/fn/${grid_type_str}.hpp>
     #include <gridtools/fn/sid_neighbor_table.hpp>
     #include <gridtools/stencil/global_parameter.hpp>
+    #include <gridtools/stencil/positional.hpp>
+
+    // TODO(havogt): move to gtfn?
+    namespace gridtools{
+    namespace fn{
+    template <class T>
+    auto index(T){
+    return stencil::positional<std::decay_t<T>>();}
+    }
+    }
+
 
     namespace generated{
 

src/gt4py/next/program_processors/codegens/gtfn/gtfn_ir.py

@@ -153,7 +153,7 @@ class StencilExecution(Stmt):
     backend: Backend
     stencil: SymRef
     output: Union[SymRef, SidComposite]
-    inputs: list[Union[SymRef, SidComposite, SidFromScalar]]
+    inputs: list[Union[SymRef, SidComposite, SidFromScalar, FunCall]]
 
 
 class Scan(Node):
@@ -192,6 +192,7 @@ class TemporaryAllocation(Node):
     "unstructured_domain",
     "named_range",
     "reduce",
+    "index",
 ]
 ARITHMETIC_BUILTINS = itir.ARITHMETIC_BUILTINS
 TYPEBUILTINS = itir.TYPEBUILTINS

src/gt4py/next/program_processors/codegens/gtfn/itir_to_gtfn_ir.py

@@ -611,7 +611,6 @@ def convert_el_to_sid(el_expr: Expr, el_type: ts.ScalarType | ts.FieldType) -> E
                 tuple_constructor=lambda *elements: SidComposite(values=list(elements)),
             )
 
-            assert isinstance(lowered_input_as_sid, (SidComposite, SidFromScalar, SymRef))
             lowered_inputs.append(lowered_input_as_sid)
 
         backend = Backend(domain=self.visit(domain, stencil=stencil, **kwargs))

src/gt4py/next/program_processors/runners/dace_iterator/__init__.py

@@ -198,10 +198,10 @@ def __sdfg__(self, *args, **kwargs) -> dace.sdfg.sdfg.SDFG:
         # Add them as dynamic properties to the SDFG
 
         input_fields = [
-            str(in_field.id)
+            str(in_field.id)  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
             for closure in self.itir.closures
             for in_field in closure.inputs
-            if str(in_field.id) in fields
+            if str(in_field.id) in fields  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
         ]
         sdfg.gt4py_program_input_fields = {
             in_field: dim
@@ -237,11 +237,11 @@ def __sdfg__(self, *args, **kwargs) -> dace.sdfg.sdfg.SDFG:
                 closure.stencil, num_args=len(closure.inputs)
             )
             for param, shifts in zip(closure.inputs, params_shifts):
-                if not isinstance(param.id, str):
+                if not isinstance(param.id, str):  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
                     continue
-                if param.id not in sdfg.gt4py_program_input_fields:
+                if param.id not in sdfg.gt4py_program_input_fields:  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
                     continue
-                sdfg.offset_providers_per_input_field.setdefault(param.id, []).extend(list(shifts))
+                sdfg.offset_providers_per_input_field.setdefault(param.id, []).extend(list(shifts))  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
 
         return sdfg
 

src/gt4py/next/program_processors/runners/dace_iterator/itir_to_sdfg.py

@@ -357,7 +357,10 @@ def visit_StencilClosure(
         closure_state = closure_sdfg.add_state("closure_entry")
         closure_init_state = closure_sdfg.add_state_before(closure_state, "closure_init", True)
 
-        input_names = [str(inp.id) for inp in node.inputs]
+        assert all(
+            isinstance(inp, SymRef) for inp in node.inputs
+        )  # backend only supports SymRef inputs, not `index` calls
+        input_names = [str(inp.id) for inp in node.inputs]  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
         neighbor_tables = get_used_connectivities(node, self.offset_provider)
         connectivity_names = [
             dace_utils.connectivity_identifier(offset) for offset in neighbor_tables.keys()
@@ -565,7 +568,7 @@ def _visit_scan_stencil_closure(
 
         assert isinstance(node.output, SymRef)
         neighbor_tables = get_used_connectivities(node, self.offset_provider)
-        input_names = [str(inp.id) for inp in node.inputs]
+        input_names = [str(inp.id) for inp in node.inputs]  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
         connectivity_names = [
             dace_utils.connectivity_identifier(offset) for offset in neighbor_tables.keys()
         ]
@@ -732,7 +735,7 @@ def _visit_parallel_stencil_closure(
         ],
     ) -> tuple[dace.SDFG, dict[str, str | dace.subsets.Subset], list[str]]:
         neighbor_tables = get_used_connectivities(node, self.offset_provider)
-        input_names = [str(inp.id) for inp in node.inputs]
+        input_names = [str(inp.id) for inp in node.inputs]  # type: ignore[union-attr]  # backend only supports SymRef inputs, not `index` calls
         connectivity_names = [
             dace_utils.connectivity_identifier(offset) for offset in neighbor_tables.keys()
         ]

tests/next_tests/definitions.py

@@ -117,6 +117,7 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
 USES_MESH_WITH_SKIP_VALUES = "uses_mesh_with_skip_values"
 USES_SCALAR_IN_DOMAIN_AND_FO = "uses_scalar_in_domain_and_fo"
 CHECKS_SPECIFIC_ERROR = "checks_specific_error"
+USES_INDEX_BUILTIN = "uses_index_builtin"
 
 # Skip messages (available format keys: 'marker', 'backend')
 UNSUPPORTED_MESSAGE = "'{marker}' tests not supported by '{backend}' backend"
@@ -127,7 +128,6 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
 # Common list of feature markers to skip
 COMMON_SKIP_TEST_LIST = [
     (REQUIRES_ATLAS, XFAIL, BINDINGS_UNSUPPORTED_MESSAGE),
-    (STARTS_FROM_GTIR_PROGRAM, SKIP, UNSUPPORTED_MESSAGE),
     (USES_APPLIED_SHIFTS, XFAIL, UNSUPPORTED_MESSAGE),
     (USES_IF_STMTS, XFAIL, UNSUPPORTED_MESSAGE),
     (USES_NEGATIVE_MODULO, XFAIL, UNSUPPORTED_MESSAGE),
@@ -145,6 +145,8 @@ class ProgramFormatterId(_PythonObjectIdMixin, str, enum.Enum):
     (USES_TUPLE_ARGS, XFAIL, UNSUPPORTED_MESSAGE),
     (USES_TUPLE_RETURNS, XFAIL, UNSUPPORTED_MESSAGE),
     (USES_ZERO_DIMENSIONAL_FIELDS, XFAIL, UNSUPPORTED_MESSAGE),
+    (USES_INDEX_BUILTIN, XFAIL, UNSUPPORTED_MESSAGE),
+    (STARTS_FROM_GTIR_PROGRAM, SKIP, UNSUPPORTED_MESSAGE),
 ]
 GTIR_DACE_SKIP_TEST_LIST = [
     (ALL, SKIP, UNSUPPORTED_MESSAGE),

tests/next_tests/integration_tests/feature_tests/iterator_tests/test_program.py

@@ -10,13 +10,22 @@
 import pytest
 
 import gt4py.next as gtx
-from gt4py.next.iterator.builtins import as_fieldop, cartesian_domain, deref, named_range
+from gt4py.next.iterator import ir as itir
+from gt4py.next.iterator.builtins import (
+    as_fieldop,
+    cartesian_domain,
+    deref,
+    index,
+    named_range,
+    shift,
+)
 from gt4py.next.iterator.runtime import fendef, fundef, set_at
 
 from next_tests.unit_tests.conftest import program_processor, run_processor
 
 
 I = gtx.Dimension("I")
+Ioff = gtx.FieldOffset("Ioff", source=I, target=(I,))
 
 
 @fundef
@@ -44,3 +53,48 @@ def test_prog(program_processor):
     run_processor(copy_program, program_processor, inp, out, isize, offset_provider={})
     if validate:
         assert np.allclose(inp.asnumpy(), out.asnumpy())
+
+
+@fendef
+def index_program_simple(out, size):
+    set_at(
+        as_fieldop(lambda i: deref(i), cartesian_domain(named_range(I, 0, size)))(index(I)),
+        cartesian_domain(named_range(I, 0, size)),
+        out,
+    )
+
+
+@pytest.mark.starts_from_gtir_program
+@pytest.mark.uses_index_builtin
+def test_index_builtin(program_processor):
+    program_processor, validate = program_processor
+
+    isize = 10
+    out = gtx.as_field([I], np.zeros(shape=(isize,)), dtype=getattr(np, itir.INTEGER_INDEX_BUILTIN))
+
+    run_processor(index_program_simple, program_processor, out, isize, offset_provider={})
+    if validate:
+        assert np.allclose(np.arange(10), out.asnumpy())
+
+
+@fendef
+def index_program_shift(out, size):
+    set_at(
+        as_fieldop(
+            lambda i: deref(i) + deref(shift(Ioff, 1)(i)), cartesian_domain(named_range(I, 0, size))
+        )(index(I)),
+        cartesian_domain(named_range(I, 0, size)),
+        out,
+    )
+
+
+@pytest.mark.uses_index_builtin
+def test_index_builtin_shift(program_processor):
+    program_processor, validate = program_processor
+
+    isize = 10
+    out = gtx.as_field([I], np.zeros(shape=(isize,)), dtype=getattr(np, itir.INTEGER_INDEX_BUILTIN))
+
+    run_processor(index_program_shift, program_processor, out, isize, offset_provider={"Ioff": I})
+    if validate:
+        assert np.allclose(np.arange(10) + np.arange(1, 11), out.asnumpy())