bpo-33041: Rework compiling an "async for" loop. (#6142)

* Added new opcode END_ASYNC_FOR.
* Setting global StopAsyncIteration no longer breaks "async for" loops.
* Jumping into an "async for" loop is now disabled.
* Jumping out of an "async for" loop no longer corrupts the stack.
* Simplify the compiler.

Lib/test/test_coroutines.py

@@ -1846,6 +1846,36 @@ class CoroutineTest(unittest.TestCase):
             run_async(run_gen()),
             ([], [121]))
 
+    def test_comp_4_2(self):
+        async def f(it):
+            for i in it:
+                yield i
+
+        async def run_list():
+            return [i + 10 async for i in f(range(5)) if 0 < i < 4]
+        self.assertEqual(
+            run_async(run_list()),
+            ([], [11, 12, 13]))
+
+        async def run_set():
+            return {i + 10 async for i in f(range(5)) if 0 < i < 4}
+        self.assertEqual(
+            run_async(run_set()),
+            ([], {11, 12, 13}))
+
+        async def run_dict():
+            return {i + 10: i + 100 async for i in f(range(5)) if 0 < i < 4}
+        self.assertEqual(
+            run_async(run_dict()),
+            ([], {11: 101, 12: 102, 13: 103}))
+
+        async def run_gen():
+            gen = (i + 10 async for i in f(range(5)) if 0 < i < 4)
+            return [g + 100 async for g in gen]
+        self.assertEqual(
+            run_async(run_gen()),
+            ([], [111, 112, 113]))
+
     def test_comp_5(self):
         async def f(it):
             for i in it: