Implement --no-strings-lazy-pp as a preprocessing pass (#5777)

This option eliminates extended functions in strings eagerly. This was incorrectly done at ppRewrite previously, which should not add lemmas. Instead, this makes this technique into a preprocessing pass. To do this, the interface for the strings preprocessor was cleaned to have fewer dependencies, and made to track a cache internally.

Fixes #5608, fixes #5745, fixes #5767, fixes #5771, fixes #5406.

4 files changed, 20 insertions, 85 deletions

diff --git a/src/theory/strings/extf_solver.cpp b/src/theory/strings/extf_solver.cpp
index 7e416d132..352da5ac8 100644
--- a/src/theory/strings/extf_solver.cpp
+++ b/src/theory/strings/extf_solver.cpp
@@ -43,7 +43,7 @@ ExtfSolver::ExtfSolver(SolverState& s,
       d_csolver(cs),
       d_extt(et),
       d_statistics(statistics),
-      d_preproc(d_termReg.getSkolemCache(), s.getUserContext(), statistics),
+      d_preproc(d_termReg.getSkolemCache(), &statistics.d_reductions),
       d_hasExtf(s.getSatContext(), false),
       d_extfInferCache(s.getSatContext()),
       d_reduced(s.getUserContext())
diff --git a/src/theory/strings/theory_strings.cpp b/src/theory/strings/theory_strings.cpp
index 3189b297a..eec59685a 100644
--- a/src/theory/strings/theory_strings.cpp
+++ b/src/theory/strings/theory_strings.cpp
@@ -1032,31 +1032,6 @@ TrustNode TheoryStrings::ppRewrite(TNode atom)
       atomRet = ret.getNode();
     }
   }
-  if( !options::stringLazyPreproc() ){
-    //eager preprocess here
-    std::vector< Node > new_nodes;
-    StringsPreprocess* p = d_esolver.getPreprocess();
-    Node pret = p->processAssertion(atomRet, new_nodes);
-    if (pret != atomRet)
-    {
-      Trace("strings-ppr") << "  rewrote " << atomRet << " -> " << pret
-                           << ", with " << new_nodes.size() << " lemmas."
-                           << std::endl;
-      for (const Node& lem : new_nodes)
-      {
-        Trace("strings-ppr") << "    lemma : " << lem << std::endl;
-        ++(d_statistics.d_lemmasEagerPreproc);
-        d_out->lemma(lem);
-      }
-      atomRet = pret;
-      // Don't support proofs yet, thus we must return nullptr. This is the
-      // case even if we had proven the elimination via regexp elimination
-      // above.
-      ret = TrustNode::mkTrustRewrite(atom, atomRet, nullptr);
-    }else{
-      Assert(new_nodes.empty());
-    }
-  }
   return ret;
 }
 
diff --git a/src/theory/strings/theory_strings_preprocess.cpp b/src/theory/strings/theory_strings_preprocess.cpp
index 1a46b26f5..f0afe5f26 100644
--- a/src/theory/strings/theory_strings_preprocess.cpp
+++ b/src/theory/strings/theory_strings_preprocess.cpp
@@ -41,9 +41,8 @@ struct QInternalVarAttributeId
 typedef expr::Attribute<QInternalVarAttributeId, Node> QInternalVarAttribute;
 
 StringsPreprocess::StringsPreprocess(SkolemCache* sc,
-                                     context::UserContext* u,
-                                     SequencesStatistics& stats)
-    : d_sc(sc), d_statistics(stats)
+                                     HistogramStat<Kind>* statReductions)
+    : d_sc(sc), d_statReductions(statReductions)
 {
 }
 
@@ -938,7 +937,10 @@ Node StringsPreprocess::simplify(Node t, std::vector<Node>& asserts)
         Trace("strings-preprocess") << "   " << asserts[i] << std::endl;
       }
     }
-    d_statistics.d_reductions << t.getKind();
+    if (d_statReductions != nullptr)
+    {
+      (*d_statReductions) << t.getKind();
+    }
   }
   else
   {
@@ -948,12 +950,11 @@ Node StringsPreprocess::simplify(Node t, std::vector<Node>& asserts)
   return retNode;
 }
 
-Node StringsPreprocess::simplifyRec(Node t,
-                                    std::vector<Node>& asserts,
-                                    std::map<Node, Node>& visited)
+Node StringsPreprocess::simplifyRec(Node t, std::vector<Node>& asserts)
 {
-  std::map< Node, Node >::iterator it = visited.find(t);
-  if( it!=visited.end() ){
+  std::map<Node, Node>::iterator it = d_visited.find(t);
+  if (it != d_visited.end())
+  {
     return it->second;
   }else{
     Node retNode = t;
@@ -968,7 +969,7 @@ Node StringsPreprocess::simplifyRec(Node t,
         cc.push_back( t.getOperator() );
       }
       for(unsigned i=0; i<t.getNumChildren(); i++) {
-        Node s = simplifyRec(t[i], asserts, visited);
+        Node s = simplifyRec(t[i], asserts);
         cc.push_back( s );
         if( s!=t[i] ) {
           changed = true;
@@ -980,22 +981,21 @@ Node StringsPreprocess::simplifyRec(Node t,
       }
       retNode = simplify(tmp, asserts);
     }
-    visited[t] = retNode;
+    d_visited[t] = retNode;
     return retNode;
   }
 }
 
 Node StringsPreprocess::processAssertion(Node n, std::vector<Node>& asserts)
 {
-  std::map< Node, Node > visited;
   std::vector<Node> asserts_curr;
-  Node ret = simplifyRec(n, asserts_curr, visited);
+  Node ret = simplifyRec(n, asserts_curr);
   while (!asserts_curr.empty())
   {
     Node curr = asserts_curr.back();
     asserts_curr.pop_back();
     std::vector<Node> asserts_tmp;
-    curr = simplifyRec(curr, asserts_tmp, visited);
+    curr = simplifyRec(curr, asserts_tmp);
     asserts_curr.insert(
         asserts_curr.end(), asserts_tmp.begin(), asserts_tmp.end());
     asserts.push_back(curr);
@@ -1003,38 +1003,6 @@ Node StringsPreprocess::processAssertion(Node n, std::vector<Node>& asserts)
   return ret;
 }
 
-void StringsPreprocess::processAssertions( std::vector< Node > &vec_node ){
-  std::map< Node, Node > visited;
-  for( unsigned i=0; i<vec_node.size(); i++ ){
-    Trace("strings-preprocess-debug") << "Preprocessing assertion " << vec_node[i] << std::endl;
-    //preprocess until fixed point
-    std::vector<Node> asserts;
-    std::vector<Node> asserts_curr;
-    asserts_curr.push_back(vec_node[i]);
-    while (!asserts_curr.empty())
-    {
-      Node curr = asserts_curr.back();
-      asserts_curr.pop_back();
-      std::vector<Node> asserts_tmp;
-      curr = simplifyRec(curr, asserts_tmp, visited);
-      asserts_curr.insert(
-          asserts_curr.end(), asserts_tmp.begin(), asserts_tmp.end());
-      asserts.push_back(curr);
-    }
-    Node res = asserts.size() == 1
-                   ? asserts[0]
-                   : NodeManager::currentNM()->mkNode(kind::AND, asserts);
-    if( res!=vec_node[i] ){
-      res = Rewriter::rewrite( res );
-      if (options::unsatCores() && !options::proofNew())
-      {
-        ProofManager::currentPM()->addDependence(res, vec_node[i]);
-      }
-      vec_node[i] = res;
-    }
-  }
-}
-
 Node StringsPreprocess::mkForallInternal(Node bvl, Node body)
 {
   NodeManager* nm = NodeManager::currentNM();
diff --git a/src/theory/strings/theory_strings_preprocess.h b/src/theory/strings/theory_strings_preprocess.h
index 124a09a4c..b156a5f5e 100644
--- a/src/theory/strings/theory_strings_preprocess.h
+++ b/src/theory/strings/theory_strings_preprocess.h
@@ -41,8 +41,7 @@ namespace strings {
 class StringsPreprocess {
  public:
   StringsPreprocess(SkolemCache* sc,
-                    context::UserContext* u,
-                    SequencesStatistics& stats);
+                    HistogramStat<Kind>* statReductions = nullptr);
   ~StringsPreprocess();
   /** The reduce routine
    *
@@ -79,27 +78,20 @@ class StringsPreprocess {
    * asserts.
    */
   Node processAssertion(Node t, std::vector<Node>& asserts);
-  /**
-   * Replaces all formulas t in vec_node with an equivalent formula t' that
-   * contains no free instances of extended functions (that is, extended
-   * functions may only appear beneath quantifiers). This applies simplifyRec
-   * on each assertion in vec_node until a fixed point is reached.
-   */
-  void processAssertions(std::vector<Node>& vec_node);
 
  private:
   /** pointer to the skolem cache used by this class */
   SkolemCache* d_sc;
   /** Reference to the statistics for the theory of strings/sequences. */
-  SequencesStatistics& d_statistics;
+  HistogramStat<Kind>* d_statReductions;
+  /** visited cache */
+  std::map<Node, Node> d_visited;
   /**
    * Applies simplify to all top-level extended function subterms of t. New
    * assertions created in this reduction are added to asserts. The argument
    * visited stores a cache of previous results.
    */
-  Node simplifyRec(Node t,
-                   std::vector<Node>& asserts,
-                   std::map<Node, Node>& visited);
+  Node simplifyRec(Node t, std::vector<Node>& asserts);
   /**
    * Make internal quantified formula with bound variable list bvl and body.
    * Internally, we get a node corresponding to marking a quantified formula as