gh-148874: add flag to CALL to skip periodic check in with

Doc/library/dis.rst

@@ -77,7 +77,7 @@ the following command can be used to display the disassembly of
    <BLANKLINE>
      3           LOAD_GLOBAL              1 (len + NULL)
                  LOAD_FAST_BORROW         0 (alist)
-                 CALL                     1
+                 CALL                     3 (1)
                  RETURN_VALUE
 
 (The "2" is a line number).
@@ -1601,6 +1601,10 @@ iterations of the loop.
    .. versionchanged:: 3.13
       Calls with keyword arguments are now handled by :opcode:`CALL_KW`.
 
+   .. versionchanged:: next
+      ``argc`` is now the oparg shifted right by one. The low bit indicates
+      whether the call is interruptible.
+
 
 .. opcode:: CALL_KW (argc)
 

Include/internal/pycore_magic_number.h

@@ -296,6 +296,7 @@ Known values:
     Python 3.15a8 3663 (Merge GET_ITER and GET_YIELD_FROM_ITER. Modify SEND to make it a bit more like FOR_ITER)
     Python 3.15a8 3664 (Fix __qualname__ for __annotate__ functions)
     Python 3.15a8 3665 (Add FOR_ITER_VIRTUAL and GET_ITER specializations)
+    Python 3.15a9 3666 (Pack CALL oparg as (argcount<<1) | interruptible; gh-148874)
 
 
     Python 3.16 will start with 3700
@@ -309,7 +310,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3665
+#define PYC_MAGIC_NUMBER 3666
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \