add (disabled) stubs for decomposing re-membership on regex

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/ast/rewriter/seq_rewriter.cpp

@@ -2109,6 +2109,34 @@ bool seq_rewriter::get_head_tail_reversed(expr* s, expr_ref& head, expr_ref& tai
     return false;
 }
 
+bool seq_rewriter::get_re_head_tail(expr* r, expr_ref& head, expr_ref& tail) {
+    expr* r1 = nullptr, *r2 = nullptr;
+    if (re().is_concat(r, r1, r2)) {
+        head = r1;
+        tail = r2;
+        return re().min_length(r1) != UINT_MAX && re().max_length(r1) == re().min_length(r1);
+    }
+    return false;
+}
+
+bool seq_rewriter::get_re_head_tail_reversed(expr* r, expr_ref& head, expr_ref& tail) {
+    expr* r1 = nullptr, *r2 = nullptr;
+    if (re().is_concat(r, r1, r2)) {
+        unsigned len = re().min_length(r2);
+        if (len != UINT_MAX && re().max_length(r2) == len) {
+            head = r1;
+            tail = r2;
+            return true;
+        }
+        if (get_re_head_tail_reversed(r2, head, tail)) {
+            head = re().mk_concat(r1, head);
+            return true;
+        }
+    }
+    return false;
+}
+
+
 expr_ref seq_rewriter::re_and(expr* cond, expr* r) {
     if (m().is_true(cond))
         return expr_ref(r, m());    
@@ -2586,6 +2614,21 @@ bool seq_rewriter::rewrite_contains_pattern(expr* a, expr* b, expr_ref& result)
     "" in b -> is_nullable(b)
     (ele + tail) in b -> tail in (derivative e b)
     (head + ele) in b -> head in (right-derivative e b)
+
+Other rewrites:
+    s in b1 ++ b2, min_len(b1) = max_len(b2) != UINT_MAX -> 
+           (seq.len s) >= min_len(b1) & 
+           (seq.extract s 0 min_len(b1)) in b1 & 
+           (seq.extract s min_len(b1) (- (seq.len s) min_len(b1))) in b2
+
+    similar for tail of regex
+
+Disabled rewrite:
+   s + "ab" + t in all ++ "c" ++ all ++ .... ++ "z" ++ all
+   => 
+   disjunctions that cover cases where s overlaps given that "ab" does
+   not overlap with any of the sequences.
+   It is disabled because the solver doesn't handle disjunctions of regexes well.
 */
 br_status seq_rewriter::mk_str_in_regexp(expr* a, expr* b, expr_ref& result) {
 
@@ -2615,14 +2658,35 @@ br_status seq_rewriter::mk_str_in_regexp(expr* a, expr* b, expr_ref& result) {
         result = re().mk_in_re(tl, re().mk_derivative(hd, b));
         return BR_REWRITE2;
     }
-    else if (get_head_tail_reversed(a, hd, tl)) {
-        result = re().mk_in_re(
-            hd,
-            re().mk_reverse(re().mk_derivative(tl, re().mk_reverse(b)))
-        );
+
+    if (get_head_tail_reversed(a, hd, tl)) {
+        result = re().mk_reverse(re().mk_derivative(tl, re().mk_reverse(b)));
+        result = re().mk_in_re(hd, result);
         return BR_REWRITE_FULL;
     }
 
+#if 0
+    if (get_re_head_tail(b, hd, tl)) {
+        SASSERT(re().min_length(hd) == re().max_length(hd));
+        expr_ref len_hd(m_autil.mk_int(re().min_length(hd)), m()); 
+        expr_ref len_a(str().mk_length(a), m());
+        expr_ref len_tl(m_autil.mk_sub(len_a, len_hd), m());
+        result = m().mk_and(m_autil.mk_ge(len_a, len_hd),
+                            re().mk_in_re(str().mk_substr(a, m_autil.mk_int(0), len_hd), hd),
+                            re().mk_in_re(str().mk_substr(a, len_hd, len_tl), tl));
+        return BR_REWRITE_FULL;
+    }
+    if (get_re_head_tail_reversed(b, hd, tl)) {
+        SASSERT(re().min_length(tl) == re().max_length(tl));
+        expr_ref len_tl(m_autil.mk_int(re().min_length(tl)), m()); 
+        expr_ref len_a(str().mk_length(a), m());
+        expr_ref len_hd(m_autil.mk_sub(len_a, len_tl), m());
+        result = m().mk_and(m_autil.mk_ge(len_a, len_tl),
+                            re().mk_in_re(str().mk_substr(a, m_autil.mk_int(0), len_hd), hd),
+                            re().mk_in_re(str().mk_substr(a, len_hd, len_tl), tl));
+        return BR_REWRITE_FULL;
+    }
+#endif
     if (false && rewrite_contains_pattern(a, b, result))
         return BR_REWRITE_FULL;
 

src/ast/rewriter/seq_rewriter.h

@@ -136,6 +136,8 @@ class seq_rewriter {
     // Support for regular expression derivatives
     bool get_head_tail(expr* e, expr_ref& head, expr_ref& tail);
     bool get_head_tail_reversed(expr* e, expr_ref& head, expr_ref& tail);
+    bool get_re_head_tail(expr* e, expr_ref& head, expr_ref& tail);
+    bool get_re_head_tail_reversed(expr* e, expr_ref& head, expr_ref& tail);
     expr_ref re_and(expr* cond, expr* r);
     expr_ref re_predicate(expr* cond, sort* seq_sort);
     expr_ref mk_seq_concat(expr* a, expr* b);    

src/ast/seq_decl_plugin.cpp

@@ -1155,6 +1155,13 @@ bv_util& seq_util::bv() const {
     return *m_bv.get();
 }
 
+unsigned seq_util::max_plus(unsigned x, unsigned y) const {
+    if (x + y < x || x + y < y)
+        return UINT_MAX;
+    return x + y;
+}
+
+
 bool seq_util::is_const_char(expr* e, unsigned& c) const {
 #if Z3_USE_UNICODE
     return is_app_of(e, m_fid, OP_CHAR_CONST) && (c = to_app(e)->get_parameter(0).get_int(), true);
@@ -1243,15 +1250,49 @@ app* seq_util::str::mk_is_empty(expr* s) const {
     return m.mk_eq(s, mk_empty(get_sort(s)));
 }
 
+
+
 unsigned seq_util::str::min_length(expr* s) const {
     SASSERT(u.is_seq(s));
-    expr_ref_vector es(m);
     unsigned result = 0;
-    get_concat_units(s, es);
-    for (expr* arg : es) {
-        if (is_unit(arg))
-            result++;
+    expr* s1 = nullptr, *s2 = nullptr;
+    auto get_length = [&](expr* s1) {
+        zstring st;
+        if (is_unit(s1))
+            return 1u;
+        else if (is_string(s1, st))
+            return st.length();
+        else
+            return 0u;
+    };
+    while (is_concat(s, s1, s2)) {
+        result += get_length(s1);
+        s = s2;
     }
+    result += get_length(s);
+    return result;
+}
+
+unsigned seq_util::str::max_length(expr* s) const {
+    SASSERT(u.is_seq(s));
+    unsigned result = 0;
+    expr* s1 = nullptr, *s2 = nullptr;
+    zstring st;
+    auto get_length = [&](expr* s1) {
+        if (is_empty(s1))
+            return 0u;
+        else if (is_unit(s1))
+            return 1u;
+        else if (is_string(s1, st))
+            return st.length();
+        else
+            return UINT_MAX;
+    };
+    while (is_concat(s, s1, s2)) {
+        result = u.max_plus(get_length(s), result);
+        s = s2;
+    }
+    result = u.max_plus(get_length(s), result);
     return result;
 }
 
@@ -1260,15 +1301,8 @@ unsigned seq_util::re::min_length(expr* r) const {
     expr* r1 = nullptr, *r2 = nullptr, *s = nullptr;
     if (is_empty(r))
         return UINT_MAX;
-    if (is_concat(r, r1, r2)) {
-        unsigned l1 = min_length(r1);
-        if (l1 == UINT_MAX)
-            return l1;
-        unsigned l2 = min_length(r2);
-        if (l2 == UINT_MAX)
-            return l2;
-        return l1 + l2;
-    }
+    if (is_concat(r, r1, r2)) 
+        return u.max_plus(min_length(r1), min_length(r2));
     if (m.is_ite(r, s, r1, r2)) 
         return std::min(min_length(r1), min_length(r2));
     if (is_diff(r, r1, r2))
@@ -1282,6 +1316,26 @@ unsigned seq_util::re::min_length(expr* r) const {
     return 0;
 }
 
+unsigned seq_util::re::max_length(expr* r) const {
+    SASSERT(u.is_re(r));
+    expr* r1 = nullptr, *r2 = nullptr, *s = nullptr;
+    if (is_empty(r))
+        return 0;
+    if (is_concat(r, r1, r2)) 
+        return u.max_plus(max_length(r1), max_length(r2));
+    if (m.is_ite(r, s, r1, r2)) 
+        return std::max(max_length(r1), max_length(r2));
+    if (is_diff(r, r1, r2))
+        return max_length(r1);
+    if (is_union(r, r1, r2)) 
+        return std::max(max_length(r1), max_length(r2));
+    if (is_intersection(r, r1, r2)) 
+        return std::min(max_length(r1), max_length(r2));
+    if (is_to_re(r, s)) 
+        return u.str.max_length(s);
+    return UINT_MAX;
+}
+
 sort* seq_util::re::to_seq(sort* re) {
     (void)u;
     SASSERT(u.is_re(re));

src/ast/seq_decl_plugin.h

@@ -236,6 +236,8 @@ class seq_util {
     family_id m_fid;
     mutable scoped_ptr<bv_util> m_bv;
     bv_util& bv() const;
+
+    unsigned max_plus(unsigned x, unsigned y) const;
 public:
 
     ast_manager& get_manager() const { return m; }
@@ -400,6 +402,7 @@ public:
         expr* get_rightmost_concat(expr* e) const { expr* e1, *e2; while (is_concat(e, e1, e2)) e = e2; return e; }
 
         unsigned min_length(expr* s) const;
+        unsigned max_length(expr* s) const;
     };
 
     class re {
@@ -469,6 +472,7 @@ public:
         bool is_loop(expr const* n, expr*& body, expr*& lo, expr*& hi);
         bool is_loop(expr const* n, expr*& body, expr*& lo);
         unsigned min_length(expr* r) const;
+        unsigned max_length(expr* r) const;
     };
     str str;
     re  re;