fix[cartesian]: DaCe array access in tasklet (#1410)

Found some incompatible tasklet representation while upgrading to dace v0.15.1. Array access inside tasklet with partial index subset worked in v0.14.1, although not valid.
The fix consists of modifying the memlets to pass the full array shape to such tasklet, and use all explicit indices inside the tasklet to access the array. This is the right representation in DaCe SDFG, as discussed with the DaCe developers.

src/gt4py/cartesian/gtc/dace/expansion/daceir_builder.py

@@ -30,6 +30,7 @@
     compute_dcir_access_infos,
     flatten_list,
     get_tasklet_symbol,
+    make_dace_subset,
     union_inout_memlets,
     union_node_grid_subsets,
     untile_memlets,
@@ -458,6 +459,40 @@ def visit_HorizontalExecution(
             write_memlets=write_memlets,
         )
 
+        for memlet in [*read_memlets, *write_memlets]:
+            """
+            This loop handles the special case of a tasklet performing array access.
+            The memlet should pass the full array shape (no tiling) and
+            the tasklet expression for array access should use all explicit indexes.
+            """
+            array_ndims = len(global_ctx.arrays[memlet.field].shape)
+            field_decl = global_ctx.library_node.field_decls[memlet.field]
+            # calculate array subset on original memlet
+            memlet_subset = make_dace_subset(
+                global_ctx.library_node.access_infos[memlet.field],
+                memlet.access_info,
+                field_decl.data_dims,
+            )
+            # select index values for single-point grid access
+            memlet_data_index = [
+                dcir.Literal(value=str(dim_range[0]), dtype=common.DataType.INT32)
+                for dim_range, dim_size in zip(memlet_subset, memlet_subset.size())
+                if dim_size == 1
+            ]
+            if len(memlet_data_index) < array_ndims:
+                reshape_memlet = False
+                for access_node in dcir_node.walk_values().if_isinstance(dcir.IndexAccess):
+                    if access_node.data_index and access_node.name == memlet.connector:
+                        access_node.data_index = memlet_data_index + access_node.data_index
+                        assert len(access_node.data_index) == array_ndims
+                        reshape_memlet = True
+                if reshape_memlet:
+                    # ensure that memlet symbols used for array indexing are defined in context
+                    for sym in memlet.access_info.grid_subset.free_symbols:
+                        symbol_collector.add_symbol(sym)
+                    # set full shape on memlet
+                    memlet.access_info = global_ctx.library_node.access_infos[memlet.field]
+
         for item in reversed(expansion_items):
             iteration_ctx = iteration_ctx.pop()
             dcir_node = self._process_iteration_item(

src/gt4py/cartesian/gtc/daceir.py

@@ -536,7 +536,7 @@ def union(self, other):
             else:
                 assert (
                     isinstance(interval2, (TileInterval, DomainInterval))
-                    and isinstance(interval1, IndexWithExtent)
+                    and isinstance(interval1, (IndexWithExtent, DomainInterval))
                 ) or (
                     isinstance(interval1, (TileInterval, DomainInterval))
                     and isinstance(interval2, IndexWithExtent)
@@ -573,7 +573,7 @@ def overapproximated_shape(self):
     def apply_iteration(self, grid_subset: GridSubset):
         res_intervals = dict(self.grid_subset.intervals)
         for axis, field_interval in self.grid_subset.intervals.items():
-            if axis in grid_subset.intervals:
+            if axis in grid_subset.intervals and not isinstance(field_interval, DomainInterval):
                 grid_interval = grid_subset.intervals[axis]
                 assert isinstance(field_interval, IndexWithExtent)
                 extent = field_interval.extent