Redundant NOP is generated in -OO mode

[serhiy-storchaka]

Run test_dis:

$ ./python -OO -m test -vuall test_dis
...
======================================================================
FAIL: test_disassemble_recursive (test.test_dis.DisTests.test_disassemble_recursive)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_dis.py", line 1105, in test_disassemble_recursive
    check(dis_nested_1, depth=1)
    ~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/serhiy/py/cpython/Lib/test/test_dis.py", line 1102, in check
    self.assertEqual(dis, expected)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
AssertionError: '  --[771 chars]\n 725           NOP\n\n 726           LOAD_GL[532 chars]UE\n' != '  --[771 chars]\n 726           LOAD_GLOBAL              1 (l[510 chars]UE\n'
    --           MAKE_CELL                0 (y)
  
   723           RESUME                   0
  
   724           LOAD_FAST                0 (y)
                 BUILD_TUPLE              1
                 LOAD_CONST               1 (<code object foo at 0x..., file "/home/serhiy/py/cpython/Lib/test/test_dis.py", line 724>)
                 MAKE_FUNCTION
                 SET_FUNCTION_ATTRIBUTE   8 (closure)
                 STORE_FAST               1 (foo)
  
   727           LOAD_FAST                1 (foo)
                 RETURN_VALUE
  
  Disassembly of <code object foo at 0x..., file "/home/serhiy/py/cpython/Lib/test/test_dis.py", line 724>:
    --           COPY_FREE_VARS           1
                 MAKE_CELL                0 (x)
  
   724           RESUME                   0
  
-  725           NOP
- 
   726           LOAD_GLOBAL              1 (list + NULL)
                 LOAD_FAST                0 (x)
                 BUILD_TUPLE              1
                 LOAD_CONST               1 (<code object <genexpr> at 0x..., file "/home/serhiy/py/cpython/Lib/test/test_dis.py", line 726>)
                 MAKE_FUNCTION
                 SET_FUNCTION_ATTRIBUTE   8 (closure)
                 LOAD_DEREF               1 (y)
                 GET_ITER
                 CALL                     0
                 CALL                     1
                 RETURN_VALUE

Linked PRs

• gh-115347: avoid emitting redundant NOP for the docstring with -OO #115494

[sobolevn]

cc @iritkatriel