feature: make prune_noops a pass and allow pass statement

As title

numba_rvsdg/core/datastructures/ast_transforms.py

@@ -70,10 +70,8 @@ def seal_inside_loop(
         """
         if self.is_continue():
             self.set_jump_targets(head_index)
-            self.instructions.pop()
         elif self.is_break():
             self.set_jump_targets(exit_index)
-            self.instructions.pop()
         elif self.is_return():
             pass
         else:
@@ -89,7 +87,7 @@ def to_dict(self) -> dict[str, Any]:
     def __repr__(self) -> str:
         return (
             f"WritableASTBlock({self.name}, "
-            "{self.instructions}, {self.jump_targets})"
+            f"{self.instructions}, {self.jump_targets})"
         )
 
 
@@ -134,6 +132,20 @@ def prune_unreachable(self) -> set[WritableASTBlock]:
         self.unreachable = unreachable
         return unreachable
 
+    def prune_noops(self) -> set[type[ast.AST]]:
+        """Prune no-op instructions from the CFG."""
+        noops = set()
+        exclude = (ast.Pass, ast.Continue, ast.Break)
+        for block in self.values():
+            block.instructions = [
+                i for i in block.instructions if not isinstance(i, exclude)
+            ]
+            noops.update(
+                [i for i in block.instructions if isinstance(i, exclude)]
+            )
+        self.noops = noops
+        return noops  # type: ignore
+
     def prune_empty(self) -> set[WritableASTBlock]:
         """Prune empty blocks from the CFG."""
         empty = set()
@@ -230,6 +242,7 @@ def transform(self) -> None:
         # Prune if requested.
         if self.prune:
             _ = self.blocks.prune_unreachable()
+            _ = self.blocks.prune_noops()
             _ = self.blocks.prune_empty()
 
     def codegen(self, tree: list[type[ast.AST]] | list[ast.stmt]) -> None:
@@ -257,6 +270,7 @@ def handle_ast_node(self, node: type[ast.AST] | ast.stmt) -> None:
                 ast.Return,
                 ast.Break,
                 ast.Continue,
+                ast.Pass,
             ),
         ):
             self.current_block.instructions.append(node)

numba_rvsdg/tests/test_ast_transforms.py

@@ -49,6 +49,19 @@ def function() -> None:
         }
         self.compare(function, expected)
 
+    def test_solo_pass(self):
+        def function() -> None:
+            pass
+
+        expected = {
+            "0": {
+                "instructions": ["return"],
+                "jump_targets": [],
+                "name": "0",
+            }
+        }
+        self.compare(function, expected)
+
     def test_assign_return(self):
         def function() -> int:
             x = 1