Add Skolem cache for strings, refactor length registration (#2457)

This PR is in preparation for doing more aggressive caching of skolems (for example, in the strings preprocessor).

It refactors sendLengthLemma -> registerLength, which unifies how length lemmas for skolems and other string terms are handled.

1 files changed, 50 insertions, 0 deletions

diff --git a/src/theory/strings/skolem_cache.cpp b/src/theory/strings/skolem_cache.cpp
new file mode 100644
index 000000000..db673dafe
--- /dev/null
+++ b/src/theory/strings/skolem_cache.cpp
@@ -0,0 +1,50 @@
+/*********************                                                        */
+/*! \file skolem_cache.cpp
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds
+ ** This file is part of the CVC4 project.
+ ** Copyright (c) 2009-2018 by the authors listed in the file AUTHORS
+ ** in the top-level source directory) and their institutional affiliations.
+ ** All rights reserved.  See the file COPYING in the top-level source
+ ** directory for licensing information.\endverbatim
+ **
+ ** \brief Implementation of a cache of skolems for theory of strings.
+ **/
+
+#include "theory/strings/skolem_cache.h"
+
+namespace CVC4 {
+namespace theory {
+namespace strings {
+
+SkolemCache::SkolemCache() {}
+
+Node SkolemCache::mkSkolemCached(Node a, Node b, SkolemId id, const char* c)
+{
+  std::map<SkolemId, Node>::iterator it = d_skolemCache[a][b].find(id);
+  if (it == d_skolemCache[a][b].end())
+  {
+    Node sk = mkSkolem(c);
+    d_skolemCache[a][b][id] = sk;
+    return sk;
+  }
+  return it->second;
+}
+
+Node SkolemCache::mkSkolem(const char* c)
+{
+  NodeManager* nm = NodeManager::currentNM();
+  Node n = nm->mkSkolem(c, nm->stringType(), "string skolem");
+  d_allSkolems.insert(n);
+  return n;
+}
+
+bool SkolemCache::isSkolem(Node n) const
+{
+  return d_allSkolems.find(n) != d_allSkolems.end();
+}
+
+}  // namespace strings
+}  // namespace theory
+}  // namespace CVC4