JIT: Assertion failure in `_PyOptimizer_Optimize`

# Crash report

### What happened?

It's possible to abort a patched debug JIT build by running the code below. The interpreter must be called from a venv in which lafleur is installed as editable, likely due to that priming the GC into a state suitable for the crash.

Sorry about the convoluted reproduction steps.

The necessary patch is:
```diff
diff --git a/Include/internal/pycore_backoff.h b/Include/internal/pycore_backoff.h
index 23ca7299e0d..0289b5fee7c 100644
--- a/Include/internal/pycore_backoff.h
+++ b/Include/internal/pycore_backoff.h
@@ -124,7 +124,7 @@ trigger_backoff_counter(void)
 // For example, 4095 does not work for the nqueens benchmark on pyperformance
 // as we always end up tracing the loop iteration's
 // exhaustion iteration. Which aborts our current tracer.
-#define JUMP_BACKWARD_INITIAL_VALUE 4000
+#define JUMP_BACKWARD_INITIAL_VALUE 63
 #define JUMP_BACKWARD_INITIAL_BACKOFF 6
 static inline _Py_BackoffCounter
 initial_jump_backoff_counter(void)
@@ -137,7 +137,7 @@ initial_jump_backoff_counter(void)
 * Must be larger than ADAPTIVE_COOLDOWN_VALUE,
 * otherwise when a side exit warms up we may construct
 * a new trace before the Tier 1 code has properly re-specialized. */
-#define SIDE_EXIT_INITIAL_VALUE 4000
+#define SIDE_EXIT_INITIAL_VALUE 63
 #define SIDE_EXIT_INITIAL_BACKOFF 6

 static inline _Py_BackoffCounter
```

To install lafleur as editable, first create a venv and activate it, then clone the [lafleur repo](https://github.com/devdanzin/lafleur/) and run `pip install -e /path/to/lafleur/clone`.


This MRE must be invoked like this:

```
/path/to/venv/with/editable/lafleur/install/bin/python mre.py
```

MRE:
```python
import asyncio
any_v2 = None
tuple_v4 = (1, "")

def f1():
 class A:
 def _():...
 def __(): ...
 def ___():...

 class B: ...
 class C:
 def _(): ... 
 class D:
 def _(): ... 
 class E:
 def _(): ... 
 class F:
 def _(): ... 
 class G:
 def _(): ... 
 class H:
 def _(): ... 
 
 l = []
 for i in range(5):
 def _(): ...
 class I:
 async def _(): ...
 try:
 c = _()
 except Exception: ...

 def __(): ...
 class J:
 def _(): ...

 for _ in range(300):
 try:
 try: ValueError("")
 except E: ...
 except Exception: ...
 (
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2, any_v2,
 any_v2, any_v2, 
 )
 class K:
 def _():...
 def __(): ...
 def ___():...
 class AsyncCtx_9078:
 def _(self): ...
 async def __():
 try:
 for _ in K(10): ...
 except Exception: ...
 try:
 c = __()
 except Exception: ...
 x, *y = tuple_v4
 class L:
 def _():...
 def __(): ...
 def ___():...
 class M:
 def _(self): ...
 async def __():
 try:
 for _ in L(10): ...
 except Exception: ...
 try:
 c = __()
 except Exception: ...

 x, *y = x, *y = tuple_v4
 class M:
 def _():...
 def __(): ...
 def ___():...
 class N:
 def _():...
 def __(): ...
 def ___():...
 class O:
 def _(self): ...
 async def __():
 try:
 for _ in N(10): ...
 except Exception: ...
 try:
 c = __()
 except Exception: ...
 class P:
 def _():...
 def __(): ...
 def ___():...
 class Q:
 def _(self): ...
 async def __():
 try:
 with Q(): ...
 except Exception: ...
 try:
 c = __()
 except Exception: ...
 class R:
 def _(self): ...
 async def __():
 try:
 with R(): ...
 except Exception: ...
 try:
 c = __()
 except Exception: ...

 x, *y = x, *y = tuple_v4
 class S:
 def __init__(self, lit):
 selit = self.count = 0
 def __aiter__(self):return self
 async def __anext__(self):
 if self.count: n
 self.count += 1
 class T:
 def _(self): ...
 async def __():
 try:
 async for _ in S(10): ...
 except Exception: ...
 try:
 c = __()
 while True:
 try: c.send(None)
 except Exception: break
 except Exception: ...

for i in range(300):
 print(i)
 f1()
```

Traceback:
```
1
[...]
200
201
python: Python/optimizer.c:144: int _PyOptimizer_Optimize(_PyInterpreterFrame *, PyThreadState *): Assertion `_tstate->jit_tracer_state.initial_state.func != NULL' failed.

Program received signal SIGABRT, Aborted.

#0 __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=0) at ./nptl/pthread_kill.c:44
#1 __pthread_kill_internal (threadid=<optimized out>, signo=6) at ./nptl/pthread_kill.c:89
#2 __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=6) at ./nptl/pthread_kill.c:100
#3 0x00007ffff7c45e2e in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4 0x00007ffff7c28888 in __GI_abort () at ./stdlib/abort.c:77
#5 0x00007ffff7c287f0 in __assert_fail_base (fmt=<optimized out>, assertion=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>) at ./assert/assert.c:118
#6 0x00007ffff7c3c19f in __assert_fail (assertion=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>) at ./assert/assert.c:127
#7 0x00005555563c0bd0 in _PyOptimizer_Optimize (frame=frame@entry=0x7e8ff6de5298, tstate=tstate@entry=0x555556e62830 <_PyRuntime+358864>) at Python/optimizer.c:144
#8 0x0000555555ed2e64 in stop_tracing_and_jit (tstate=0x555556e62830 <_PyRuntime+358864>, frame=frame@entry=0x7e8ff6de5298) at Python/ceval.c:1405
#9 0x0000555555e8eeed in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=<optimized out>, throwflag=<optimized out>) at Python/generated_cases.c.h:11628
#10 0x0000555555e6bf98 in _PyEval_EvalFrame (tstate=0x555556e62830 <_PyRuntime+358864>, frame=0x7e8ff6de5220, throwflag=0) at ./Include/internal/pycore_ceval.h:119
#11 _PyEval_Vector (tstate=<optimized out>, func=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=<optimized out>, kwnames=0x0) at Python/ceval.c:2483
#12 0x0000555555e6b9b5 in PyEval_EvalCode (co=<optimized out>, globals=<optimized out>, locals=0x7c7ff6e86440) at Python/ceval.c:1008
```

Output from running with `PYTHON_LLTRACE=4 PYTHON_OPT_DEBUG=4`:
[830_abort_lltrace_opt_debug.txt](https://github.com/user-attachments/files/24319421/830_abort_lltrace_opt_debug.txt)

Found using [lafleur](https://github.com/devdanzin/lafleur/).



### CPython versions tested on:

CPython main branch

### Operating systems tested on:

Linux

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

Python 3.15.0a3+ (heads/main-dirty:3cc57505e53, Dec 23 2025, 19:04:15) [Clang 21.1.2 (2ubuntu6)]


### Linked PRs
* gh-143126

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JIT: Assertion failure in `_PyOptimizer_Optimize`#143123

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

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JIT: Assertion failure in _PyOptimizer_Optimize#143123

Description

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

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

Linked PRs

Metadata

Metadata

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Labels

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JIT: Assertion failure in `_PyOptimizer_Optimize`#143123