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Detect empty regex membership via re_is_empty fallback; fix test build

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block_if_empty relied solely on the AST-identity state graph for dead-state
detection, which never closes on intersections/complements whose derivative
product states do not canonicalize. For ground regexes, fall back to the
antimirov NFA reachability check (re_is_empty), the same procedure propagate_eq
already uses for re.none equalities. Resolves str.in_re emptiness timeouts on
inter(., comp(.)) regexes (e.g. z3test 5728, parts of 5721).

Also drop a stale is_antimirov_union reference left in seq_regex_bisim.cpp after
the operator removal (test-z3 did not compile) and update a now-stale comment.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Margus Veanes 2026-06-26 08:47:55 +03:00
parent 92b349c669
commit 6af8b4a11d
3 changed files with 13 additions and 2 deletions
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11
src/smt/seq_regex.cpp
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@ -224,6 +224,17 @@ namespace smt {
th.add_axiom(~lit);
return true;
}
// Fall back to antimirov NFA reachability. The lazy state graph
// keys states by AST identity and cannot close on intersections /
// complements whose derivative product states do not canonicalize,
// so it never detects their emptiness. re_is_empty decides
// emptiness directly (the same procedure propagate_eq already uses
// for re.none equalities).
if (re_is_empty(r) == l_true) {
STRACE(seq_regex_brief, tout << "(empty:re) ";);
th.add_axiom(~lit);
return true;
}
}
return false;
}