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Z3 4.16.0 introduced a cube-and-conquer parallel solver that regressed easy QF_LIRA problems from <1s to hanging indefinitely. Workers start with a 1000-conflict budget and multiply by 1.5× on each timeout, but after ~38 escalations the `unsigned` cast overflows, causing the budget to oscillate chaotically (e.g. 3.27B → 618M → 927M → … never reaching a stable large value). For sub-cubes that require more conflicts than any value in the oscillation window, the worker loops forever. ## Changes - **`src/smt/smt_parallel.h`** – `update_max_thread_conflicts()`: replace raw `(unsigned)(mul * val)` cast with saturating arithmetic that caps at `UINT_MAX`, eliminating the UB and the oscillation: ```cpp // Before – UB when product > UINT_MAX, budget oscillates after ~38 escalations m_config.m_threads_max_conflicts = (unsigned)(m_config.m_max_conflict_mul * m_config.m_threads_max_conflicts); // After – saturates at UINT_MAX double next = m_config.m_max_conflict_mul * m_config.m_threads_max_conflicts; m_config.m_threads_max_conflicts = (next >= (double)UINT_MAX) ? UINT_MAX : (unsigned)next; ``` - **`src/solver/parallel_tactical.cpp`** – Identical saturating-arithmetic fix in the `parallel_tactical2` worker's `update_max_thread_conflicts()`, which is the code path actually exercised for QF_LIRA problems. - **`src/smt/smt_parallel.cpp`** – Worker's initial per-cube conflict budget is now sourced from `m_smt_params.m_threads_max_conflicts` (the user-visible `smt.threads.max_conflicts` parameter) instead of being hardcoded to 1000, so users who leave the parameter at its default get an unlimited initial budget matching Z3 4.12.x portfolio behaviour. --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: Nikolaj Bjorner <nbjorner@microsoft.com> |
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| ackermannization | ||
| api | ||
| ast | ||
| cmd_context | ||
| math | ||
| model | ||
| muz | ||
| nlsat | ||
| opt | ||
| params | ||
| parsers | ||
| qe | ||
| sat | ||
| shell | ||
| smt | ||
| solver | ||
| tactic | ||
| test | ||
| util | ||
| CMakeLists.txt | ||