## 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 ·
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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 ·
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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.
Implemented the largest cube heuristic from Bromberger and Weidenbach's
paper on cubes. Also fixes an overflow bug in mzp.
Use vswhere to find the visual studio version on windows in the build's ymls.
---------
Signed-off-by: Lev Nachmanson <levnach@hotmail.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
