misc: add ShrinkException for easy test case shrinking

xdsl/utils/exceptions.py

@@ -39,6 +39,30 @@ class InvalidIRException(Exception):
     pass
 
 
+class ShrinkException(Exception):
+    """
+    Exception used for shrinking purposes.
+
+    When using DRMacIver's [Shrink Ray](https://github.com/DRMacIver/shrinkray) library,
+    this exception can be used to reduce test cases. For example, to find a smaller
+    version of a case that has some behavior you are interested in, raise this exception
+    on the line of code you want to hit, and pass the `--shrink` argument to `xdsl-opt`.
+
+    Shrinkray currently requires the executable passed in to take no arguments, so to
+    shrink a test case like this one that raises a ShrinkException when you call it like
+    this: `xdsl-opt input_file.mlir -p my,pass,pipeline`, you need to create a new
+    executable `.sh` file with the following contents:
+
+    ```sh
+    xdsl-opt -p my,pass,pipeline --shrink
+    ```
+
+    It can then be invoked with `shrinkray FILENAME.sh input_file.mlir`.
+    """
+
+    pass
+
+
 class InterpretationError(Exception):
     """
     An error that can be raised during interpretation, or Interpreter setup.

xdsl/xdsl_opt_main.py

@@ -13,7 +13,7 @@
 from xdsl.printer import Printer
 from xdsl.tools.command_line_tool import CommandLineTool
 from xdsl.transforms import get_all_passes
-from xdsl.utils.exceptions import DiagnosticException
+from xdsl.utils.exceptions import DiagnosticException, ShrinkException
 from xdsl.utils.parse_pipeline import parse_pipeline
 
 
@@ -75,9 +75,16 @@ def run(self):
                     output_stream.flush()
                 finally:
                     chunk.close()
+        except ShrinkException:
+            assert self.args.shrink
+            print("Success, can shrink")
+            exit(0)
         finally:
             if output_stream is not sys.stdout:
                 output_stream.close()
+        if self.args.shrink:
+            print("Failure, can't shrink")
+            exit(1)
 
     def register_all_arguments(self, arg_parser: argparse.ArgumentParser):
         """
@@ -171,6 +178,13 @@ def register_all_arguments(self, arg_parser: argparse.ArgumentParser):
             version=f"xdsl-opt built from xdsl version {version('xdsl')}\n",
         )
 
+        arg_parser.add_argument(
+            "--shrink",
+            default=False,
+            action="store_true",
+            help="Return success on exit if ShrinkException was raised.",
+        )
+
     def register_pass(
         self, pass_name: str, pass_factory: Callable[[], type[ModulePass]]
     ):