fix types and linting

src/pystencils/backend/kernelcreation/cpu_optimization.py

@@ -22,8 +22,8 @@ def optimize_cpu(
     canonicalize = CanonicalizeSymbols(ctx, True)
     kernel_ast = cast(PsBlock, canonicalize(kernel_ast))
 
-    # hoist_invariants = HoistLoopInvariantDeclarations(ctx)
-    # kernel_ast = cast(PsBlock, hoist_invariants(kernel_ast))
+    hoist_invariants = HoistLoopInvariantDeclarations(ctx)
+    kernel_ast = cast(PsBlock, hoist_invariants(kernel_ast))
 
     if cfg is None:
         return kernel_ast

src/pystencils/backend/kernelcreation/typification.py

@@ -24,7 +24,6 @@ from ..ast.structural import (
     PsExpression,
     PsAssignment,
     PsDeclaration,
-    PsStatement,
     PsEmptyLeafMixIn,
 )
 from ..ast.expressions import (
@@ -704,6 +703,7 @@ class Typifier:
                                     )
                                 items_tc.apply_dtype(deconstify(elem_type))
                                 tc.infer_dtype(expr)
+                                return None
 
                             case DereferencableTo(elem_type_or_hint):
                                 if isinstance(elem_type_or_hint, PsType):