mirror of
https://github.com/Z3Prover/z3
synced 2026-07-15 11:35:42 +00:00
26ad30bb76
`seq.foldl` could produce a concrete sequence model while related
`seq.nth` constraints were still validated against stale or
underconstrained length information, leading to invalid models. In the
reported case, `all` was modeled as `(seq.++ (seq.unit 7) (seq.unit 0))`
while `final = (seq.nth all 0)` remained inconsistent with `final = 6`.
- **Root cause**
- Sequence solutions were propagated as equalities, but parent `seq.len`
terms were not updated when a sequence term was solved.
- As a result, `seq.nth` guard reasoning could miss that a solved
sequence had known in-bounds length.
- **Solver change**
- Extend `theory_seq::add_solution` to collect parent `seq.len`
expressions of a solved term when the solved result is sequence-typed.
- After propagating the solved sequence equality, also propagate the
rewritten length equality for those parent length terms.
- Keep this propagation guarded to sequence results so scalar
`seq.foldl`/`seq.foldli` solutions do not regress from `sat` to
`unknown` under model validation.
- **Regression coverage**
- Add a focused test for the reported SMT-LIB pattern:
- `all = seq.foldl(...)`
- `final = seq.nth all 0`
- `initial = 0`
- `final = 6`
- Add focused scalar `seq.foldl`/`seq.foldli` model-validation coverage
for the existing benchmark shapes that must continue returning `sat`.
- The regressions check both that model validation no longer reports an
invalid model for the `seq.nth` case and that scalar fold/foldi cases do
not regress to `unknown`.
- **Effect**
- Solved sequence terms now push enough derived length information for
dependent `seq.nth` constraints to validate against the actual modeled
sequence.
- Existing scalar fold/foldi solving behavior is preserved.
```smt2
(define-fun all_sums ((prev_sums (Seq Int)) (elem Int)) (Seq Int)
(seq.++ (seq.unit (+ (seq.nth prev_sums 0) elem)) prev_sums)
)
(assert (= all (seq.foldl all_sums (seq.unit initial) elements)))
(assert (= final (seq.nth all 0)))
(assert (= initial 0))
(assert (= final 6))
```
---------
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
|
||
|---|---|---|
| .. | ||
| ackermannization | ||
| api | ||
| ast | ||
| cmd_context | ||
| math | ||
| model | ||
| muz | ||
| nlsat | ||
| opt | ||
| params | ||
| parsers | ||
| qe | ||
| sat | ||
| shell | ||
| smt | ||
| solver | ||
| tactic | ||
| test | ||
| util | ||
| CMakeLists.txt | ||