After introducing the rewriter.sort_disjunctions option (#6774), I
noticed a segfault in a Z3 run that was working fine for me before the
PR.
I traced the difference to a slight discrepancy between the first patch
I submitted and the one we ended up merging: my first version would skip
sorting the disjuncts in mk_nflat_core, but still return BR_DONE, while
the patch in master returns BR_FAILED instead.
This patch fixes that problem, and it makes slightly more sense to me to
return a BR_DONE since, if `s` is true, some disjunct (e.g. a `false`
or a repeat) might have been simplified away. However I don't fully
understand this code.
... and I can't say I understand why the segfault happens. Perhaps that
is a separate issue?
This is the file to reproduce:
https://gist.github.com/mtzguido/b7360c74d3d2e42d89f1bd9149ad26f6
Here's a stack trace of the failure, mk_nflat_or_core is not involved.
```
(gdb) where
#0 0x0000555555b98497 in smt::context::get_lit_assignment(unsigned int) const ()
#1 0x0000555555b984cb in smt::context::get_assignment(sat::literal) const ()
#2 0x0000555555b98504 in smt::context::get_assignment(unsigned int) const ()
#3 0x0000555555ca83b8 in smt::context::get_assignment_core(expr*) const ()
#4 0x0000555555c9af5a in smt::context::get_assignment(expr*) const ()
#5 0x0000555555d7bd1d in (anonymous namespace)::has_child_assigned_to(smt::context&, app*, lbool, expr*&, unsigned int) ()
#6 0x0000555555d7c413 in (anonymous namespace)::rel_case_split_queue::next_case_split_core(ptr_vector<expr>&, unsigned int&, unsigned int&, lbool&) ()
#7 0x0000555555d7c589 in (anonymous namespace)::rel_case_split_queue::next_case_split(unsigned int&, lbool&) ()
#8 0x0000555555c9c1b7 in smt::context::decide() ()
#9 0x0000555555ca39fd in smt::context::bounded_search() ()
#10 0x0000555555ca30c2 in smt::context::search() ()
#11 0x0000555555ca273d in smt::context::check(unsigned int, expr* const*, bool) ()
#12 0x0000555555cb166a in smt::kernel::check(unsigned int, expr* const*) ()
#13 0x0000555555cb9695 in (anonymous namespace)::smt_solver::check_sat_core2(unsigned int, expr* const*) ()
#14 0x00005555560dc0c6 in solver_na2as::check_sat_core(unsigned int, expr* const*) ()
#15 0x00005555560d73f3 in combined_solver::check_sat_core(unsigned int, expr* const*) ()
#16 0x00005555560d34e3 in solver::check_sat(unsigned int, expr* const*) ()
#17 0x0000555556097b26 in cmd_context::check_sat(unsigned int, expr* const*) ()
#18 0x0000555556082ff0 in smt2::parser::parse_check_sat() ()
#19 0x0000555556084dc0 in smt2::parser::parse_cmd() ()
#20 0x00005555560861b6 in smt2::parser::operator()() ()
#21 0x00005555560757e6 in parse_smt2_commands(cmd_context&, std::basic_istream<char, std::char_traits<char> >&, bool, params_ref const&, char const*) ()
#22 0x00005555555e8f68 in read_smtlib2_commands(char const*) ()
#23 0x00005555555ee6f6 in main ()
(gdb)
```
* patterns: add option for pattern decomposition (pi.decompose_patterns)
True by default, retaining current behavior.
* rewriter: add option for sorting of disjunctions (rewriter.sort_disjunctions)
True by default, retaining current behavior.
destructive equality resolution uses an occurs check function that is only safe for quantifier-free formulas. In the special case where a bound variable is Boolean and occurs on a side of an equality the other side cannot have a quantifier.
* Logical names for function declarations in c++
Currently, for example, the function declaration symbol member for
checking whether multiplication *does not* overflow is called
`m_bv_smul_ovfl`. Since we are introducing the upcoming smtlib2 symbols
that check that multpliciation *does* overflow, the not overflow check
symbols are renamed to `m_bv_smul_no_ovfl` etc.
* Implement smtlib overflow preds for multiplication
Smtlib2 is being extended to include overflow predicates for bit
vectors (see https://groups.google.com/u/1/g/smt-lib/c/J4D99wT0aKI).
This commit introduces the predicates `bvumulo` and `bvsmulo` that
return `true` if the unsigned multiplication overflows or the signed
multiplication underflows or overflows, respectively.
* Move mul overflow predicates to BV logic
* Add a todo on illogical argument order
* Implement mk_unary_pred for bv
* Implement bvnego
* Implement bvuaddo
* Implement bvsaddo
* Implement bvusubo
* Implement bvssubo
* Implement bvsdivo
deals with fluke regression for F* reported by Guido Martinez
Background:
The automatic pattern inference facility looks for terms that contains all bound variables of a quantifier. It may end up with a term that contains all bound variables but the extracted term can be simplified.
Example. The pattern
(ApplyTT (ApplyTT @x3!1 (ApplyTT @x4!0 (:var 1))) (ApplyTT @x4!0 (:var 0)))
can be decomposed into a multi-pattern
(ApplyTT @x4!0 (:var 1))) (ApplyTT @x4!0 (:var 0))
The multi-pattern may enable a quantifier instantiation while the original pattern does not. The multi-pattern should be preferred.
The regression showed up based on a change that should not be considered harmful but turned out to be noticeable.
The change was a simplification of and-or expressions based on sorting. This played with the case split queue used by F* (smt.case_split = 3) that uses a top-level case split of clauses to avoid redundant branches. The net effect was that without sorting, the benchmarks would always choose the opportune branch that enabled matching against the larger term. With sorting it would mostly choose inopportune branches.
- add option pp.no_lets (default = false) to print formulas without let (used by the low-level SMT2 printer).
- print lemmas2console faster by using the low level printer
