gh-91432: Replace JUMP+FOR_ITER with FOR_END

Doc/library/dis.rst

@@ -1014,12 +1014,15 @@ iterations of the loop.
       The oparg is now a relative delta rather than an absolute target.
 
 
-.. opcode:: FOR_ITER (delta)
+.. opcode:: FOR_END (delta)
 
    TOS is an :term:`iterator`.  Call its :meth:`~iterator.__next__` method.  If
    this yields a new value, push it on the stack (leaving the iterator below
-   it).  If the iterator indicates it is exhausted, TOS is popped, and the byte
-   code counter is incremented by *delta*.
+   it), then decrement the bytecode counter by *delta*.  If the iterator
+   indicates it is exhausted, then pop TOS and do not decrement the bytecode
+   counter.
+
+   .. versionadded:: 3.11
 
 
 .. opcode:: LOAD_GLOBAL (namei)

Doc/whatsnew/3.11.rst

@@ -978,6 +978,12 @@ CPython bytecode changes
   relative rather than absolute.
 
 
+* Replaced :opcode:`FOR_ITER` (jumps if iterator exhausted)
+  with :opcode:`FOR_END` (jumps if iterator is not exhausted).
+  At the end of each ``for``-loop iteration, instead of an unconditional
+  jump targeted at a conditional jump, there is now
+  only one (conditional) jump.
+
 Deprecated
 ==========
 

Lib/dis.py

@@ -30,7 +30,6 @@
 LOAD_CONST = opmap['LOAD_CONST']
 LOAD_GLOBAL = opmap['LOAD_GLOBAL']
 BINARY_OP = opmap['BINARY_OP']
-JUMP_BACKWARD = opmap['JUMP_BACKWARD']
 
 CACHE = opmap["CACHE"]
 
@@ -412,7 +411,8 @@ def parse_exception_table(code):
         return entries
 
 def _is_backward_jump(op):
-    return 'JUMP_BACKWARD' in opname[op]
+    name = opname[op]
+    return 'JUMP_BACKWARD' in name or name == "FOR_END"
 
 def _get_instructions_bytes(code, varname_from_oparg=None,
                             names=None, co_consts=None,

Lib/importlib/_bootstrap_external.py

@@ -416,7 +416,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3493).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3494).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 

Lib/opcode.py

@@ -111,7 +111,6 @@ def jabs_op(name, op, entries=0):
 name_op('STORE_NAME', 90)       # Index in name list
 name_op('DELETE_NAME', 91)      # ""
 def_op('UNPACK_SEQUENCE', 92, 1)   # Number of tuple items
-jrel_op('FOR_ITER', 93)
 def_op('UNPACK_EX', 94)
 name_op('STORE_ATTR', 95, 4)       # Index in name list
 name_op('DELETE_ATTR', 96)      # ""
@@ -201,6 +200,7 @@ def jabs_op(name, op, entries=0):
 jrel_op('POP_JUMP_BACKWARD_IF_NONE', 174)
 jrel_op('POP_JUMP_BACKWARD_IF_FALSE', 175)
 jrel_op('POP_JUMP_BACKWARD_IF_TRUE', 176)
+jrel_op('FOR_END', 177)
 
 
 del def_op, name_op, jrel_op, jabs_op
@@ -267,6 +267,9 @@ def jabs_op(name, op, entries=0):
     "JUMP_BACKWARD": [
         "JUMP_BACKWARD_QUICK",
     ],
+    "FOR_END": [
+        "FOR_END_QUICK",
+    ],
     "LOAD_ATTR": [
         "LOAD_ATTR_ADAPTIVE",
         "LOAD_ATTR_INSTANCE_VALUE",

Lib/test/test__opcode.py

@@ -37,10 +37,10 @@ def test_stack_effect_jump(self):
         self.assertEqual(stack_effect(JUMP_IF_TRUE_OR_POP, 0), 0)
         self.assertEqual(stack_effect(JUMP_IF_TRUE_OR_POP, 0, jump=True), 0)
         self.assertEqual(stack_effect(JUMP_IF_TRUE_OR_POP, 0, jump=False), -1)
-        FOR_ITER = dis.opmap['FOR_ITER']
-        self.assertEqual(stack_effect(FOR_ITER, 0), 1)
-        self.assertEqual(stack_effect(FOR_ITER, 0, jump=True), -1)
-        self.assertEqual(stack_effect(FOR_ITER, 0, jump=False), 1)
+        FOR_END = dis.opmap['FOR_END']
+        self.assertEqual(stack_effect(FOR_END, 0), 1)
+        self.assertEqual(stack_effect(FOR_END, 0, jump=True), 1)
+        self.assertEqual(stack_effect(FOR_END, 0, jump=False), -1)
         JUMP_FORWARD = dis.opmap['JUMP_FORWARD']
         self.assertEqual(stack_effect(JUMP_FORWARD, 0), 0)
         self.assertEqual(stack_effect(JUMP_FORWARD, 0, jump=True), 0)

Lib/test/test_dis.py

@@ -146,12 +146,13 @@ def bug708901():
 %3d        PRECALL                           2
            CALL                              2
            GET_ITER
-        >> FOR_ITER                          2 (to 40)
-           STORE_FAST                        0 (res)
+           JUMP_FORWARD                      2 (to 40)
+        >> STORE_FAST                        0 (res)
 
-%3d        JUMP_BACKWARD                     3 (to 34)
+%3d        NOP
 
-%3d     >> LOAD_CONST                        0 (None)
+%3d     >> FOR_END                           3 (to 36)
+           LOAD_CONST                        0 (None)
            RETURN_VALUE
 """ % (bug708901.__code__.co_firstlineno,
        bug708901.__code__.co_firstlineno + 1,
@@ -569,14 +570,14 @@ def foo(x):
 %3d        RESUME                            0
            BUILD_LIST                        0
            LOAD_FAST                         0 (.0)
-        >> FOR_ITER                          7 (to 24)
-           STORE_FAST                        1 (z)
+           JUMP_FORWARD                      6 (to 22)
+        >> STORE_FAST                        1 (z)
            LOAD_DEREF                        2 (x)
            LOAD_FAST                         1 (z)
            BINARY_OP                         0 (+)
            LIST_APPEND                       2
-           JUMP_BACKWARD                     8 (to 8)
-        >> RETURN_VALUE
+        >> FOR_END                           7 (to 10)
+           RETURN_VALUE
 """ % (dis_nested_1,
        __file__,
        _h.__code__.co_firstlineno + 3,
@@ -616,17 +617,17 @@ def loop_test():
               8 LOAD_CONST                        2 (3)
              10 BINARY_OP_ADAPTIVE                5 (*)
              14 GET_ITER
-             16 FOR_ITER                         17 (to 52)
+             16 JUMP_FORWARD                     16 (to 50)
              18 STORE_FAST                        0 (i)
 
 %3d          20 LOAD_GLOBAL_MODULE                1 (NULL + load_test)
              32 LOAD_FAST                         0 (i)
              34 PRECALL_PYFUNC                    1
              38 CALL_PY_WITH_DEFAULTS             1
              48 POP_TOP
-             50 JUMP_BACKWARD_QUICK              18 (to 16)
 
-%3d     >>   52 LOAD_CONST                        0 (None)
+%3d     >>   50 FOR_END_QUICK                    17 (to 18)
+             52 LOAD_CONST                        0 (None)
              54 RETURN_VALUE
 """ % (loop_test.__code__.co_firstlineno,
        loop_test.__code__.co_firstlineno + 1,
@@ -1352,8 +1353,8 @@ def _prepare_test_cases():
   Instruction(opname='PRECALL', opcode=166, arg=1, argval=1, argrepr='', offset=16, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='CALL', opcode=171, arg=1, argval=1, argrepr='', offset=20, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='GET_ITER', opcode=68, arg=None, argval=None, argrepr='', offset=30, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='FOR_ITER', opcode=93, arg=32, argval=98, argrepr='to 98', offset=32, starts_line=None, is_jump_target=True, positions=None),
-  Instruction(opname='STORE_FAST', opcode=125, arg=0, argval='i', argrepr='i', offset=34, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='JUMP_FORWARD', opcode=110, arg=31, argval=96, argrepr='to 96', offset=32, starts_line=None, is_jump_target=True, positions=None),
+  Instruction(opname='STORE_FAST', opcode=125, arg=0, argval='i', argrepr='i', offset=34, starts_line=None, is_jump_target=True, positions=None),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=3, argval='print', argrepr='NULL + print', offset=36, starts_line=4, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_FAST', opcode=124, arg=0, argval='i', argrepr='i', offset=48, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='PRECALL', opcode=166, arg=1, argval=1, argrepr='', offset=50, starts_line=None, is_jump_target=False, positions=None),
@@ -1370,8 +1371,8 @@ def _prepare_test_cases():
   Instruction(opname='POP_JUMP_FORWARD_IF_FALSE', opcode=114, arg=2, argval=96, argrepr='to 96', offset=90, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=92, starts_line=8, is_jump_target=False, positions=None),
   Instruction(opname='JUMP_FORWARD', opcode=110, arg=16, argval=128, argrepr='to 128', offset=94, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='JUMP_BACKWARD', opcode=140, arg=33, argval=32, argrepr='to 32', offset=96, starts_line=7, is_jump_target=True, positions=None),
-  Instruction(opname='LOAD_GLOBAL', opcode=116, arg=3, argval='print', argrepr='NULL + print', offset=98, starts_line=10, is_jump_target=True, positions=None),
+  Instruction(opname='FOR_END', opcode=177, arg=32, argval=34, argrepr='to 34', offset=96, starts_line=3, is_jump_target=True, positions=None),
+  Instruction(opname='LOAD_GLOBAL', opcode=116, arg=3, argval='print', argrepr='NULL + print', offset=98, starts_line=10, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='I can haz else clause?', argrepr="'I can haz else clause?'", offset=110, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='PRECALL', opcode=166, arg=1, argval=1, argrepr='', offset=112, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='CALL', opcode=171, arg=1, argval=1, argrepr='', offset=116, starts_line=None, is_jump_target=False, positions=None),