fix[next]: make past_to_itir cached in default transforms

src/gt4py/next/backend.py

@@ -67,7 +67,7 @@ class FieldopTransformWorkflow(workflow.NamedStepSequenceWithArgs):
         dataclasses.field(default=past_process_args.past_process_args)
     )
     past_to_itir: workflow.Workflow[ffront_stages.PastClosure, stages.ProgramCall] = (
-        dataclasses.field(default_factory=past_to_itir.PastToItirFactory)
+        dataclasses.field(default_factory=lambda: past_to_itir.PastToItirFactory(cached=True))
     )
 
     foast_to_itir: workflow.Workflow[ffront_stages.FoastOperatorDefinition, itir.Expr] = (
@@ -123,7 +123,7 @@ class ProgramTransformWorkflow(workflow.NamedStepSequenceWithArgs):
         )
     )
     past_to_itir: workflow.Workflow[ffront_stages.PastClosure, stages.ProgramCall] = (
-        dataclasses.field(default_factory=past_to_itir.PastToItirFactory)
+        dataclasses.field(default_factory=lambda: past_to_itir.PastToItirFactory(cached=True))
     )
 
 
@@ -167,3 +167,4 @@ def __gt_allocator__(
         self,
     ) -> next_allocators.FieldBufferAllocatorProtocol[core_defs.DeviceTypeT]:
         return self.allocator
+        return self.allocator

src/gt4py/next/ffront/past_to_itir.py

@@ -31,38 +31,56 @@
 from gt4py.next.type_system import type_info, type_specifications as ts
 
 
+@workflow.make_step
+def past_to_itir(inp: ffront_stages.PastProgramDefinition) -> stages.ProgramCall:
+    all_closure_vars = transform_utils._get_closure_vars_recursively(inp.closure_vars)
+    offsets_and_dimensions = transform_utils._filter_closure_vars_by_type(
+        all_closure_vars, fbuiltins.FieldOffset, common.Dimension
+    )
+    grid_type = transform_utils._deduce_grid_type(inp.grid_type, offsets_and_dimensions.values())
+
+    gt_callables = transform_utils._filter_closure_vars_by_type(
+        all_closure_vars, gtcallable.GTCallable
+    ).values()
+    lowered_funcs = [gt_callable.__gt_itir__() for gt_callable in gt_callables]
+
+    itir_program = ProgramLowering.apply(
+        inp.past_node, function_definitions=lowered_funcs, grid_type=grid_type
+    )
+
+    return stages.ProgramCall(
+        program=itir_program, args=tuple(), kwargs={"column_axis": _column_axis(all_closure_vars)}
+    )
+
+
 @dataclasses.dataclass(frozen=True)
 class PastToItir(workflow.ChainableWorkflowMixin):
-    def __call__(self, inp: ffront_stages.PastClosure) -> stages.ProgramCall:
-        all_closure_vars = transform_utils._get_closure_vars_recursively(inp.closure_vars)
-        offsets_and_dimensions = transform_utils._filter_closure_vars_by_type(
-            all_closure_vars, fbuiltins.FieldOffset, common.Dimension
-        )
-        grid_type = transform_utils._deduce_grid_type(
-            inp.grid_type, offsets_and_dimensions.values()
-        )
-
-        gt_callables = transform_utils._filter_closure_vars_by_type(
-            all_closure_vars, gtcallable.GTCallable
-        ).values()
-        lowered_funcs = [gt_callable.__gt_itir__() for gt_callable in gt_callables]
+    inner: workflow.Workflow[ffront_stages.PastProgramDefinition, stages.ProgramCall] = past_to_itir
 
-        itir_program = ProgramLowering.apply(
-            inp.past_node, function_definitions=lowered_funcs, grid_type=grid_type
+    def __call__(self, inp: ffront_stages.PastClosure) -> stages.ProgramCall:
+        program_call = self.inner(
+            ffront_stages.PastProgramDefinition(inp.past_node, inp.closure_vars, inp.grid_type)
         )
 
         if config.DEBUG or "debug" in inp.kwargs:
-            devtools.debug(itir_program)
+            devtools.debug(program_call.program)
 
-        return stages.ProgramCall(
-            itir_program, inp.args, inp.kwargs | {"column_axis": _column_axis(all_closure_vars)}
+        return dataclasses.replace(
+            program_call, args=inp.args, kwargs=inp.kwargs | program_call.kwargs
         )
 
 
 class PastToItirFactory(factory.Factory):
     class Meta:
         model = PastToItir
 
+    class Params:
+        cached = factory.Trait(
+            inner=workflow.CachedStep(past_to_itir, hash_function=ffront_stages.fingerprint_stage)
+        )
+
+    inner = past_to_itir
+
 
 def _column_axis(all_closure_vars: dict[str, Any]) -> Optional[common.Dimension]:
     # construct mapping from column axis to scan operators defined on

src/gt4py/next/ffront/stages.py

@@ -85,6 +85,21 @@ class PastClosure:
     kwargs: dict[str, Any]
 
 
+def fingerprint_past_closure_noargs(
+    past_closure: PastClosure, algorithm: Optional[str | xtyping.HashlibAlgorithm] = None
+) -> str:
+    return fingerprint_stage(
+        obj={
+            "closure_vars": past_closure.closure_vars,
+            "past_node": past_closure.past_node,
+            "grid_type": past_closure.grid_type,
+            "args": past_closure.args,
+            "kwargs": past_closure.kwargs,
+        },
+        algorithm=algorithm,
+    )
+
+
 def fingerprint_stage(obj: Any, algorithm: Optional[str | xtyping.HashlibAlgorithm] = None) -> str:
     hasher: xtyping.HashlibAlgorithm
     if not algorithm: