add parameter to enable splitting guided by length constraints

src/smt/params/smt_params.h

@@ -26,6 +26,7 @@ Revision History:
 #include "smt/params/theory_array_params.h"
 #include "smt/params/theory_bv_params.h"
 #include "smt/params/theory_str_params.h"
+#include "smt/params/theory_seq_params.h"
 #include "smt/params/theory_pb_params.h"
 #include "smt/params/theory_datatype_params.h"
 #include "smt/params/preprocessor_params.h"
@@ -79,6 +80,7 @@ struct smt_params : public preprocessor_params,
                     public theory_array_params,
                     public theory_bv_params,
                     public theory_str_params,
+                    public theory_seq_params,
                     public theory_pb_params,
                     public theory_datatype_params {
     bool             m_display_proof;

src/smt/params/smt_params_helper.pyg

@@ -71,6 +71,7 @@ def_module_params(module_name='smt',
                           ('theory_case_split', BOOL, False, 'Allow the context to use heuristics involving theory case splits, which are a set of literals of which exactly one can be assigned True. If this option is false, the context will generate extra axioms to enforce this instead.'),
                           ('string_solver', SYMBOL, 'seq', 'solver for string/sequence theories. options are: \'z3str3\' (specialized string solver), \'seq\' (sequence solver), \'auto\' (use static features to choose best solver)'),
                           ('core.validate', BOOL, False, 'validate unsat core produced by SMT context'),
+                          ('seq.split_w_len', BOOL, True, 'enable splitting guided by length constraints'),
                           ('str.strong_arrangements', BOOL, True, 'assert equivalences instead of implications when generating string arrangement axioms'),
                           ('str.aggressive_length_testing', BOOL, False, 'prioritize testing concrete length values over generating more options'),
                           ('str.aggressive_value_testing', BOOL, False, 'prioritize testing concrete string constant values over generating more options'),

src/smt/params/theory_seq_params.cpp

@@ -0,0 +1,23 @@
+/*++
+Copyright (c) 2018 Microsoft Corporation
+
+Module Name:
+
+    theory_seq_params.cpp
+
+Abstract:
+
+    Parameters for sequence theory plugin
+
+Revision History:
+
+
+--*/
+
+#include "smt/params/theory_seq_params.h"
+#include "smt/params/smt_params_helper.hpp"
+
+void theory_seq_params::updt_params(params_ref const & _p) {
+    smt_params_helper p(_p);
+    m_split_w_len = p.seq_split_w_len();
+}

src/smt/params/theory_seq_params.h

@@ -0,0 +1,38 @@
+/*++
+Copyright (c) 2018 Microsoft Corporation
+
+Module Name:
+
+    theory_seq_params.h
+
+Abstract:
+
+    Parameters for sequence theory plugin
+
+Revision History:
+
+
+--*/
+
+#ifndef THEORY_SEQ_PARAMS_H
+#define THEORY_SEQ_PARAMS_H
+
+#include "util/params.h"
+
+struct theory_seq_params {
+    /*
+     * Enable splitting guided by length constraints
+     */
+    bool m_split_w_len;
+
+
+    theory_seq_params(params_ref const & p = params_ref()):
+        m_split_w_len(true)
+    {
+        updt_params(p);
+    }
+
+    void updt_params(params_ref const & p);
+};
+
+#endif /* THEORY_SEQ_PARAMS_H */

src/smt/smt_setup.cpp

@@ -222,7 +222,7 @@ namespace smt {
     void setup::setup_QF_BVRE() {
         setup_QF_BV();
         setup_QF_LIA();
-        m_context.register_plugin(alloc(theory_seq, m_manager));
+        m_context.register_plugin(alloc(theory_seq, m_manager, m_params));
     }
 
     void setup::setup_QF_UF(static_features const & st) {        
@@ -895,7 +895,7 @@ namespace smt {
     }
 
     void setup::setup_seq() {
-        m_context.register_plugin(alloc(smt::theory_seq, m_manager));
+        m_context.register_plugin(alloc(smt::theory_seq, m_manager, m_params));
     }
 
     void setup::setup_unknown() {

src/smt/theory_seq.cpp

@@ -191,9 +191,10 @@ void theory_seq::exclusion_table::display(std::ostream& out) const {
 }
 
 
-theory_seq::theory_seq(ast_manager& m):
+theory_seq::theory_seq(ast_manager& m, theory_seq_params const & params):
     theory(m.mk_family_id("seq")),
     m(m),
+    m_params(params),
     m_rep(m, m_dm),
     m_reset_cache(false),
     m_eq_id(0),
@@ -273,7 +274,7 @@ final_check_status theory_seq::final_check_eh() {
         TRACE("seq", tout << ">>zero_length\n";);
         return FC_CONTINUE;
     }
-    if (len_based_split()) {
+    if (m_params.m_split_w_len && len_based_split()) {
         ++m_stats.m_branch_variable;
         TRACE("seq", tout << ">>split_based_on_length\n";);
         return FC_CONTINUE;

src/smt/theory_seq.h

@@ -49,6 +49,8 @@ namespace smt {
         typedef union_find<theory_seq> th_union_find;
 
         class seq_value_proc;
+        
+        theory_seq_params const & m_params;
 
         // cache to track evaluations under equalities
         class eval_cache {
@@ -361,7 +363,7 @@ namespace smt {
         void pop_scope_eh(unsigned num_scopes) override;
         void restart_eh() override;
         void relevant_eh(app* n) override;
-        theory* mk_fresh(context* new_ctx) override { return alloc(theory_seq, new_ctx->get_manager()); }
+        theory* mk_fresh(context* new_ctx) override { return alloc(theory_seq, new_ctx->get_manager(), m_params); }
         char const * get_name() const override { return "seq"; }
         theory_var mk_var(enode* n) override;
         void apply_sort_cnstr(enode* n, sort* s) override;
@@ -621,7 +623,7 @@ namespace smt {
         void display_deps(std::ostream& out, literal_vector const& lits, enode_pair_vector const& eqs) const;
         void display_nc(std::ostream& out, nc const& nc) const;
     public:
-        theory_seq(ast_manager& m);
+        theory_seq(ast_manager& m, theory_seq_params const & params);
         ~theory_seq() override;
 
         // model building