jit: keep the adopted terminal's result when a carrier-drain walk aborts

[youknowone]

drive_bridge_carrier_walk's abort tail called fbw_finish_payload_reset()
after try_adopt_blackhole, wiping the DoneWithThisFrame* value the adopt had
just stored. The guard's caller (fbw_finish_concrete_take in call_jit.rs)
then found no concrete, and because the adopt had committed the walk-end state
it did not replay through the blackhole either, so the frame's return value
reached Python as None.

pickletools.optimize() has a single return out.getvalue(); under the JIT it
returned None and pickle.loads raised EOFError: Ran out of input
(test.test_pickletools OptimizedPickleTests.test_ints).

Clear the stash before the adopt instead. A stale sub-walk stash is still
discarded, and whatever the adopt installs survives. A declined adopt inherits
the cleared slot, so if !adopted { reset } alone would not be equivalent.
discard_bridge_carrier_walk, the only call between the adopt and the caller's
take, sets no payload.

run_perfn_walk's epilogue already guards this exact hazard
(blackhole_terminal_no_replay, "otherwise a DoneWithThisFrame result is
discarded"), but trace_bytecode returns the carrier drain's action
immediately, so that epilogue never runs on this path. A census of the four
try_adopt_blackhole call sites found this to be the only unguarded one.

Verification

	before	after
test.test_pickletools	FAILED (errors=1) ×3	OK ×3
CPython gate (108 to run, 22 skipped)	PASS 106 / FAIL 2	PASS 107 / FAIL 1

The remaining gate failure is test_re, the unrelated pre-existing defect
owned by #1122.

pyre/extra_tests/parity_tests/pickletools_optimize_bridge_abort.py is the
regression guard (0.2 s). A fixed input does not reproduce the defect — the
varying protocol/width matrix and a second round are both required.

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📥 Commits

Reviewing files that changed from the base of the PR and between 9d46d95 and 6147b27.

📒 Files selected for processing (2)

• pyre/extra_tests/parity_tests/pickletools_optimize_bridge_abort.py
• pyre/pyre-jit-trace/src/trace.rs

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[github-actions]

🤖 Codex parity review

Static analysis of this diff vs the local RPython/PyPy sources (commit 6147b27).
Updated: 2026-08-10T00:33:21.640Z

Files in the reviewed diff

pyre/extra_tests/parity_tests/pickletools_optimize_bridge_abort.py
pyre/pyre-jit-trace/src/trace.rs

1. Regressions to PyPy parity introduced by this patch

None.

2. Other mismatches introduced by this patch

None.

3. Pre-existing mismatches (already present before this patch)

None.

4. Structural adaptations

• pyre/pyre-jit-trace/src/trace.rs:2061 ↔ rpython/jit/metainterp/blackhole.py:1820 — PyPy propagates the blackhole terminal directly as a JitException; Rust’s bridge-carrier path returns to a caller and therefore uses a rooted finish-result stash. Resetting that stash immediately before adoption is the required Rust-side equivalent: it discards a sub-walk residue while preserving the newly adopted DoneWithThisFrame* result.
• pyre/extra_tests/parity_tests/pickletools_optimize_bridge_abort.py:21 ↔ no local rpython/pypy counterpart — this is a CPython-stdlib regression fixture for pickletools.optimize, not a port of PyPy/RPython source. It exercises the observable Python 3.11+/CPython-compatible behavior and introduces no runtime semantic divergence.