1 files changed, 100 insertions, 8 deletions

diff --git a/src/theory/strings/skolem_cache.cpp b/src/theory/strings/skolem_cache.cpp
index b6604d6e0..276cb70d6 100644
--- a/src/theory/strings/skolem_cache.cpp
+++ b/src/theory/strings/skolem_cache.cpp
@@ -14,10 +14,13 @@
 
 #include "theory/strings/skolem_cache.h"
 
+#include "options/strings_options.h"
 #include "theory/rewriter.h"
 #include "theory/strings/theory_strings_rewriter.h"
 #include "util/rational.h"
 
+using namespace CVC4::kind;
+
 namespace CVC4 {
 namespace theory {
 namespace strings {
@@ -42,6 +45,13 @@ Node SkolemCache::mkSkolemCached(Node a, SkolemId id, const char* c)
 Node SkolemCache::mkTypedSkolemCached(
     TypeNode tn, Node a, Node b, SkolemId id, const char* c)
 {
+  if (!options::stringsCacheSkolems())
+  {
+    Node n = NodeManager::currentNM()->mkSkolem(c, tn, "string skolem");
+    d_allSkolems.insert(n);
+    return n;
+  }
+
   a = a.isNull() ? a : Rewriter::rewrite(a);
   b = b.isNull() ? b : Rewriter::rewrite(b);
 
@@ -87,26 +97,108 @@ bool SkolemCache::isSkolem(Node n) const
 std::tuple<SkolemCache::SkolemId, Node, Node>
 SkolemCache::normalizeStringSkolem(SkolemId id, Node a, Node b)
 {
+  if (!options::stringsNormalizeSkolems())
+  {
+    return std::make_tuple(id, a, b);
+  }
+
   Trace("skolem-cache") << "normalizeStringSkolem start: (" << id << ", " << a
                         << ", " << b << ")" << std::endl;
 
-  // SK_PURIFY(str.substr x 0 (str.indexof x y 0)) ---> SK_FIRST_CTN_PRE(x, y)
+  NodeManager* nm = NodeManager::currentNM();
+
+  if (id == SK_FIRST_CTN_POST)
+  {
+    // SK_FIRST_CTN_POST(x, y) --->
+    //   SK_SUFFIX_REM(x, (+ (str.len SK_FIRST_CTN_PRE(x, y)) (str.len y)))
+    id = SK_SUFFIX_REM;
+    Node pre = mkSkolemCached(a, b, SK_FIRST_CTN_PRE, "pre");
+    b = Rewriter::rewrite(nm->mkNode(
+        PLUS, nm->mkNode(STRING_LENGTH, pre), nm->mkNode(STRING_LENGTH, b)));
+  }
+
+  if (id == SK_ID_C_SPT)
+  {
+    // SK_ID_C_SPT(x, y) ---> SK_SUFFIX_REM(x, (str.len y))
+    id = SK_SUFFIX_REM;
+    b = Rewriter::rewrite(nm->mkNode(STRING_LENGTH, b));
+  }
+  else if (id == SK_ID_VC_SPT)
+  {
+    // SK_ID_VC_SPT(x, y) ---> SK_SUFFIX_REM(x, 1)
+    id = SK_SUFFIX_REM;
+    b = nm->mkConst(Rational(1));
+  }
+  else if (id == SK_ID_VC_SPT_REV)
+  {
+    // SK_ID_VC_SPT_REV(x, y) ---> SK_PREFIX(x, (- (str.len x) 1))
+    id = SK_PREFIX;
+    b = Rewriter::rewrite(nm->mkNode(
+        MINUS, nm->mkNode(STRING_LENGTH, a), nm->mkConst(Rational(1))));
+  }
+  else if (id == SK_ID_DC_SPT)
+  {
+    // SK_ID_DC_SPT(x, y) ---> SK_PREFIX(x, 1)
+    id = SK_PREFIX;
+    b = nm->mkConst(Rational(1));
+  }
+  else if (id == SK_ID_DC_SPT_REM)
+  {
+    // SK_ID_DC_SPT_REM(x, y) ---> SK_SUFFIX_REM(x, 1)
+    id = SK_SUFFIX_REM;
+    b = nm->mkConst(Rational(1));
+  }
+  else if (id == SK_ID_DEQ_X)
+  {
+    // SK_ID_DEQ_X(x, y) ---> SK_PREFIX(y, (str.len x))
+    id = SK_PREFIX;
+    Node aOld = a;
+    a = b;
+    b = Rewriter::rewrite(nm->mkNode(STRING_LENGTH, aOld));
+  }
+  else if (id == SK_ID_DEQ_Y)
+  {
+    // SK_ID_DEQ_Y(x, y) ---> SK_PREFIX(x, (str.len y))
+    id = SK_PREFIX;
+    b = Rewriter::rewrite(nm->mkNode(STRING_LENGTH, b));
+  }
+
+  if (id == SK_SUFFIX_REM) {
+    //std::cout << "suffix" << a << " " << b << std::endl;
+  }
+
   if (id == SK_PURIFY && a.getKind() == kind::STRING_SUBSTR)
   {
     Node s = a[0];
     Node n = a[1];
     Node m = a[2];
-    if (m.getKind() == kind::STRING_STRIDOF && m[0] == s)
+
+    if (n == d_zero)
+    {
+      // SK_PURIFY((str.substr x 0 m)) ---> SK_PREFIX(x, m)
+      id = SK_PREFIX;
+      a = s;
+      b = m;
+    }
+    else if (TheoryStringsRewriter::checkEntailArith(
+                 nm->mkNode(PLUS, n, m), nm->mkNode(STRING_LENGTH, s)))
     {
-      if (n == d_zero && m[2] == d_zero)
-      {
-        id = SK_FIRST_CTN_PRE;
-        a = m[0];
-        b = m[1];
-      }
+      // SK_PURIFY((str.substr x n m)) ---> SK_SUFFIX_REM(x, n)
+      // if n + m >= (str.len x)
+      id = SK_SUFFIX_REM;
+      a = s;
+      b = n;
     }
   }
 
+  if (id == SK_PREFIX && b.getKind() == kind::STRING_STRIDOF && a == b[0]
+      && b[2] == d_zero)
+  {
+    // SK_PREFIX(x, (str.indexof x y 0)) ---> SK_FIRST_CTN_PRE(x, y)
+    id = SK_FIRST_CTN_PRE;
+    b = b[1];
+  }
+
   if (id == SK_FIRST_CTN_PRE)
   {
     // SK_FIRST_CTN_PRE((str.substr x 0 n), y) ---> SK_FIRST_CTN_PRE(x, y)