gh-134584: Eliminate redundant refcounting from _CALL_TUPLE_1

[noamcohen97]

• Issue: Eliminate redundant refcounting in the JIT #134584

[Fidget-Spinner]

Nice! That was fast. This PR LGTM, but we need to wait will Mark merges his register allocation PR to get the benefits of this work. See my other comment here #135818 (comment)

[Fidget-Spinner]

Cool. I see an ~5% improvement in this code:

def foo(): for x in range(200000000): tuple(()) return None foo() 

Before: real 0m3.497s After: real 0m3.323s 

Considering only one reference count was eliminated, this is good news for everything else that will remove more!

[Fidget-Spinner]

@markshannon sorry can you please check if this is correct? I think the ERROR_IF might be misplaced, sorry!

[Fidget-Spinner]

the generated code looks correct but I wonder if the C analyzer treats it any differently

[Fidget-Spinner]

@markshannon sorry can you please check if this is correct? I think the ERROR_IF might be misplaced, sorry!

So this seems to be the case. If you look at the error case, it leaks a reference on exit, as it doesn't decref/close it. Sorry I have to revert this PR, or provide a fix. So sorry again!

[markshannon]

I think the ERROR_IF might be misplaced, sorry!

Yes, this leaks arg

[vstinner]

I confirm that this change introduced a memory leak in the following tests:

7 tests failed: test.test_multiprocessing_fork.test_processes test.test_multiprocessing_fork.test_threads test.test_multiprocessing_forkserver.test_processes test.test_multiprocessing_forkserver.test_threads test.test_multiprocessing_spawn.test_processes test.test_multiprocessing_spawn.test_threads test_dbm_dumb 

Example AMD64 Fedora Stable Refleaks 3.x: https://buildbot.python.org/#/builders/320/builds/3425

$ ./python -m test test.test_multiprocessing_fork.test_threads -R 3:3 -m test_map_handle_iterable_exception test.test_multiprocessing_fork.test_threads leaked [4, 4, 4] references, sum=12 test.test_multiprocessing_fork.test_threads leaked [2, 2, 2] memory blocks, sum=6 

[vstinner]

@Fidget-Spinner wrote #142604 to fix the leak.

[noamcohen97]

Sorry about that! Thanks @Fidget-Spinner 🙏

[vstinner]

@Fidget-Spinner wrote #142604 to fix the leak.

He wrote another change to fix the leak: #142620.