## Summary
Fixes a hang (wall-clock timeout) in the native parallel SMT solver when
a cube is incomplete for a reason that cannot change. Originating
discussion: https://github.com/Z3Prover/bench/discussions/2746
Benchmark: `iss-3707/bug-1.smt2` (`QF_NRA`, runs with
`parallel.enable=true`).
## Divergence
The recorded oracle vs. current z3 (`z3 -T:20`):
```diff
-(incomplete (theory difference-logic))
-unknown
+timeout
```
z3 should terminate with `unknown` (incomplete theory) but instead spins
until the 20s timeout.
## Root cause
In `src/smt/smt_parallel.cpp` the per-cube worker handled an `l_undef`
cube by unconditionally calling `update_max_thread_conflicts()` and
re-splitting/re-checking. That only helps when the cube was abandoned at
the per-cube conflict limit (`max-conflicts-reached`). When the cube is
incomplete for a permanent reason (incomplete theory, quantifiers,
resource limits), the verdict never changes, so the worker re-checks the
same cube forever. The `batch_manager` had no `unknown` terminal state,
so `get_result()` could only end as sat/unsat/exception — there was no
way to settle on `unknown`, hence the hang. This is the `smt_parallel`
analogue of the `parallel_tactical.cpp` regression fixed earlier.
## Fix
Minimal, mirroring the tactic-side fix:
- add an `is_unknown` batch-manager state + `m_reason_unknown`;
- a worker reporting `l_undef` whose `last_failure` is not
`max-conflicts-reached` calls `set_unknown(reason)` and stops
re-splitting;
- `set_sat`/`set_unsat` may still override `is_unknown` so a definitive
answer wins;
- `get_result()` maps `is_unknown -> l_undef` and the reason propagates
to the parent context.
## Validation
Rebuilt z3 (`make -C build -j16`) and re-ran the benchmark 5× with
`-T:20`. Every run finished in well under the timeout with output
matching the oracle byte-for-byte:
```
(incomplete (theory difference-logic))
unknown
```
Created as a **draft** for human review.
> Generated by [Fix a Z3 snapshot-regression
divergence](https://github.com/Z3Prover/bench/actions/runs/28358375255)
· 553.9 AIC · ⌖ 27.2 AIC · ⊞ 9K ·
[◷](https://github.com/search?q=repo%3AZ3Prover%2Fz3+%22gh-aw-workflow-id%3A+snapshot-regression-fixer%22&type=pullrequests)
<!-- gh-aw-agentic-workflow: Fix a Z3 snapshot-regression divergence,
engine: copilot, version: 1.0.63, model: claude-opus-4.8, id:
28358375255, workflow_id: snapshot-regression-fixer, run:
https://github.com/Z3Prover/bench/actions/runs/28358375255 -->
<!-- gh-aw-workflow-id: snapshot-regression-fixer -->
<!-- gh-aw-workflow-call-id: Z3Prover/bench/snapshot-regression-fixer
-->
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Add new parallel algorithm as a tactic (parallel_tactical2.cpp)
Don't port over old experiments from smt_parallel that we aren't using
(sls, inprocessing, failed_literal_mode for bb detection)
Fix bugs: lease cancellation/reslimit race condition, involves changing
lease epoch to simple boolean flag
Also, now there is a single shared set of params for the tactic and
smt_parallel
**Test runs for the parallel_tactical2 vs old smt_parallel version:**
run-2747-Z3-threads-4-qflia-30s-stats.md
run-2746-Z3-threads-4-qflia-30s-parallel_tactic-stats.md
run-2745-Z3-threads-1-qfbv-30s-stats.md
run-3013-Z3-threads-4-qfbv-30s-parallel_tactic-stats.md --> note this is
indeed run-3013, I reran after a bugfix in inc_sat_solver
run-2743-Z3-threads-4-qfnia-30s-stats.md
run-2742-Z3-threads-4-qfnia-30s-parallel_tactic-stats.md
**Test runs for the new smt_parallel with bugfixes:**
run-2801-Z3-threads-4-qflia-30s-smtparallel-bugfixes-stats.md,
run-2800-Z3-threads-4-qflia-30s-smtparallel-bugfixes-stats.md
run-2797-Z3-threads-4-qfnia-30s-smtparallel-bugfixes-stats.md
compare to old smt_parallel:
run-2747-Z3-threads-4-qflia-30s-stats.md
run-2743-Z3-threads-4-qfnia-30s-stats.md
Note that there is a slight regression on lia in run-2800. The source of
this appears to be the new new LP largest-cube LIA heuristic param,
which is enabled by default. disabling this param in run-2801 restored
performance (I didn't change this in this PR though, just something to
note)
http://mtzguido.tplinkdns.com:8081/z3/compare_stats.html
---------
Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
Co-authored-by: Ilana Shapiro <ilanashapiro@Ilanas-MacBook-Pro.local>
Co-authored-by: Ilana Shapiro <ilanashapiro@Ilanas-MBP.localdomain>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
## Summary
Fixes a Z3 snapshot-regression divergence tracked in Z3Prover/bench
discussion
https://github.com/Z3Prover/bench/discussions/2662.
- **Benchmark:** `iss-5753/small-3.smt2` (Z3Prover/bench corpus,
original issue z3#5753)
- **Regression:** recorded oracle `unsat` (captured 2026-06-05) →
current `master` produces `timeout` at `-T:20`
- **bench workflow run:**
https://github.com/Z3Prover/bench/actions/runs/28078176175
### Divergence
```diff
--- small-3.expected.out (expected)
+++ produced (current z3)
@@ -1 +1 @@
-unsat
+timeout
```
The answer `unsat` is still correct — z3 simply can no longer prove it
within the
budget. This is a **performance regression**, not a wrong/unsound
result.
## Root cause
The benchmark is a quantified Array/Real/Int problem solved via MBQI.
The model
finder's quantifier analyzer (`src/smt/smt_model_finder.cpp`) now
creates a
`ho_var` qinfo for **array-sorted quantified variables used as terms**
(the new
higher-order term-enumeration path introduced in #9908, "Term
enumeration",
commit `5699142f5`). Before that commit such an occurrence set
`m_info->m_is_auf = false` (a safe fallback that left no extra
instantiation
hints), which is the behaviour that was active when the `unsat` oracle
was
captured.
`ho_var::populate_inst_sets` builds instantiation candidates with:
```cpp
for (auto t : tn.enum_terms(srt)) {
...
S->insert(t, generation);
}
```
`term_enumeration::enum_terms` is a **lazy, increasing-cost generator
with no
inherent bound** (see `ast/rewriter/term_enumeration.h`). For this
benchmark the
relevant array sort `(Array Int (Array Int Real))` has many array-valued
uninterpreted productions (`tptpummul`, `trans`, `inv`, ...), so
iterating the
generator to exhaustion inserts an explosively large number of terms
into the
instantiation set, blowing up MBQI instantiation and exhausting the 20s
budget.
Confirmed empirically: running the benchmark with `-v:3` shows
`ho_var::populate_inst_sets: 622 (Array Int (Array Int Real))`, i.e.
this exact
path fires for the divergent benchmark.
Notably, the original commit `5699142f5` declared `unsigned max_count =
20;` for
this very loop but **never applied it**, and that dead variable was
subsequently
removed — leaving the enumeration completely unbounded.
## Fix
Restore the intended bound so at most 20 of the cheapest enumerated
terms are
added to the instantiation set:
```cpp
unsigned max_count = 20;
for (auto t : tn.enum_terms(srt)) {
if (max_count == 0)
break;
--max_count;
...
S->insert(t, generation);
}
```
This is sound (instantiation only ever adds valid ground instances of
the
quantified formula) and is strictly more information than the pre-#9908
baseline
(which added no `ho_var` terms at all), so it does not regress problems
the
feature was meant to help. The change is confined to a single loop in
`src/smt/smt_model_finder.cpp`.
## Validation
Built the checkout in Release mode and re-ran the failing benchmark with
the
same options the snapshot harness uses:
```
$ build/z3 -T:20 inputs/issues/iss-5753/small-3.smt2
unsat # was: timeout
real 0m0.120s
```
The combined output now matches the recorded `small-3.expected.out`
oracle
**byte-for-byte** (`unsat\n`). A smoke run over a sample of other corpus
benchmarks showed no crashes or new divergences, and a basic
`(check-sat)/(get-model)` sanity check still works.
---
This PR is opened as a **draft** for human review by the automated
snapshot-regression fixer.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
> Generated by [Fix a Z3 snapshot-regression
divergence](https://github.com/Z3Prover/bench/actions/runs/28078343154)
· 2.8K AIC · ⌖ 150.7 AIC · ⊞ 39K ·
[◷](https://github.com/search?q=repo%3AZ3Prover%2Fz3+%22gh-aw-workflow-id%3A+snapshot-regression-fixer%22&type=pullrequests)
<!-- gh-aw-agentic-workflow: Fix a Z3 snapshot-regression divergence,
engine: copilot, version: 1.0.60, model: claude-opus-4.8, id:
28078343154, workflow_id: snapshot-regression-fixer, run:
https://github.com/Z3Prover/bench/actions/runs/28078343154 -->
<!-- gh-aw-workflow-id: snapshot-regression-fixer -->
<!-- gh-aw-workflow-call-id: Z3Prover/bench/snapshot-regression-fixer
-->
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This is another PR towards the goal of getting a clean build with clang,
using the compiler options used in building clang-tidy.
By default, without any new -W flags, clang warns about unused local
variables and private class fields. This PR deletes the handful of these
that clang found.
I'm assuming that the class "enode" in smt_context.cpp is the one in
smt_enode.h, so that
```
parent->get_expr()
```
calls a const method with no side effects.
