[mypyc] Fix compiler crash for empty async with body

mypyc/irbuild/statement.py

@@ -712,6 +712,9 @@ def transform_try_except(
     builder.builder.push_error_handler(double_except_block)
     builder.activate_block(except_entry)
     old_exc = builder.call_c(error_catch_op, [], line)
+    if builder.fn_info.is_generator:
+        # CFG cleanup may remove the CallC's block while resume cleanup paths remain.
+        old_exc = builder.ensure_register(old_exc)
     # Compile the except blocks with the nonlocal control flow overridden to clear exc_info
     builder.nonlocal_control.append(ExceptNonlocalControl(builder.nonlocal_control[-1], old_exc))
 

mypyc/test-data/run-async.test

@@ -292,8 +292,12 @@ async def async_with_vectorcall() -> str:
     async with ctx:
         return await async_val("vc")
 
+async def async_with_pass() -> None:
+    async with async_ctx():
+        pass
+
 [file driver.py]
-from native import async_with, async_with_vectorcall
+from native import async_with, async_with_pass, async_with_vectorcall
 from testutil import run_generator
 
 yields, val = run_generator(async_with(), [None, 'x', None])
@@ -304,6 +308,10 @@ yields, val = run_generator(async_with_vectorcall(), [None, 'x', None])
 assert yields == ('enter', 'vc', 'exit'), yields
 assert val == 'x', val
 
+yields, val = run_generator(async_with_pass(), [None, None])
+assert yields == ('enter', 'exit'), yields
+assert val is None
+
 [case testAsyncReturn]
 from testutil import async_val