Segfault with async generator expressions

[stestagg]

Crash report

What happened?

Running:

tuple(await 2 for _ in [])

on main causes a segfault:

backtrace

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x0000000000000000
    frame #1: 0x00000001001b1e34 python.exe`_PyForIter_VirtualIteratorNext(tstate=0x00000001004df800, frame=0x0000000100678020, iter=<unavailable>, index_ptr=<unavailable>) at ceval.c:3717:22 [opt]
    frame #2: 0x00000001001aa02c python.exe`_PyEval_EvalFrameDefault(tstate=<unavailable>, frame=0x0000000100678020, throwflag=<unavailable>) at generated_cases.c.h:6093:36 [opt]
    frame #3: 0x00000001001a2ff4 python.exe`_PyEval_EvalFrame(tstate=0x00000001004df800, frame=<unavailable>, throwflag=0) at pycore_ceval.h:118:16 [opt] [inlined]
    frame #4: 0x00000001001a2fe8 python.exe`_PyEval_Vector(tstate=0x00000001004df800, func=0x000000010514b530, locals=0x000000010514e540, args=0x0000000000000000, argcount=0, kwnames=0x0000000000000000) at ceval.c:2124:12 [opt] [inlined]
    frame #5: 0x00000001001a2fe8 python.exe`PyEval_EvalCode(co=<unavailable>, globals=0x000000010514e540, locals=0x000000010514e540) at ceval.c:686:21 [opt]
    frame #6: 0x0000000100225080 python.exe`run_eval_code_obj(tstate=<unavailable>, co=<unavailable>, globals=<unavailable>, locals=<unavailable>) at pythonrun.c:1369:12 [opt] [artificial]
    frame #7: 0x0000000100224ec0 python.exe`run_mod(mod=0x00000008ec416678, filename=0x00000001050f68d0, globals=0x000000010514e540, locals=<unavailable>, flags=<unavailable>, arena=0x000000010503a2f0, interactive_src=<unavailable>, generate_new_source=<unavailable>) at pythonrun.c:1472:19 [opt]
    frame #8: 0x0000000100222108 python.exe`pyrun_file(fp=0x0000000203f788d0, filename=0x00000001050f68d0, start=257, globals=0x000000010514e540, locals=0x000000010514e540, closeit=1, flags=0x000000016fdfe7f8) at pythonrun.c:1296:15 [opt] [inlined]
    frame #9: 0x000000010022209c python.exe`_PyRun_SimpleFileObject(fp=0x0000000203f788d0, filename=0x00000001050f68d0, closeit=1, flags=0x000000016fdfe7f8) at pythonrun.c:518:13 [opt]
    frame #10: 0x0000000100221ad8 python.exe`_PyRun_AnyFileObject(fp=0x0000000203f788d0, filename=0x00000001050f68d0, closeit=1, flags=0x000000016fdfe7f8) at pythonrun.c:81:15 [opt]
    frame #11: 0x000000010024baf0 python.exe`pymain_run_file_obj(program_name=0x00000001050f69c0, filename=0x00000001050f68d0, skip_source_first_line=0) at main.c:411:15 [opt] [inlined]
    frame #12: 0x000000010024bab4 python.exe`pymain_run_file(config=0x00000001004aa820) at main.c:430:15 [opt]
    frame #13: 0x000000010024b34c python.exe`pymain_run_python(exitcode=0x000000016fdfe8d4) at main.c:715:21 [opt] [inlined]
    frame #14: 0x000000010024af2c python.exe`Py_RunMain at main.c:796:5 [opt]
    frame #15: 0x000000010024b644 python.exe`pymain_main(args=0x000000016fdfebe0) at main.c:826:12 [opt]
    frame #16: 0x000000010024b6e4 python.exe`Py_BytesMain(argc=<unavailable>, argv=<unavailable>) at main.c:850:12 [opt]
    frame #17: 0x00000001978e1d54 dyld`start + 7184
(lldb)

The regression was introduced by:
#131738: optimize builtin any/all/tuple calls with a generator expression arg (#131737)

I'm guessing the missing syntax check means we have an async iter inside the call, and the optimized path is assunming it's a sync iter? I'm not an expert here.

Reproducible on Macos and linux builds.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.14.3 (main, Feb 19 2026, 15:40:46) [Clang 17.0.0 (clang-1700.6.3.2)]

Linked PRs

• gh-149122: Fix segfault in compiler when certain builtin functions are passed a coroutine as arg #149138

[stestagg]

Tagging the commit author: @iritkatriel

[iritkatriel]

Thank you @stestagg. I've submitted a fix.