global-negate preprocessing pass (#2317)

2 files changed, 168 insertions, 0 deletions

diff --git a/src/preprocessing/passes/global_negate.cpp b/src/preprocessing/passes/global_negate.cpp
new file mode 100644
index 000000000..ddebf961f
--- /dev/null
+++ b/src/preprocessing/passes/global_negate.cpp
@@ -0,0 +1,116 @@
+/*********************                                                        */
+/*! \file global_negate.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 global_negate
+ **/
+
+#include "preprocessing/passes/global_negate.h"
+#include <vector>
+#include "expr/node.h"
+#include "theory/rewriter.h"
+
+using namespace std;
+using namespace CVC4::kind;
+using namespace CVC4::theory;
+
+namespace CVC4 {
+namespace preprocessing {
+namespace passes {
+
+Node GlobalNegate::simplify(std::vector<Node>& assertions, NodeManager* nm)
+{
+  Assert(!assertions.empty());
+  Trace("cbqi-gn") << "Global negate : " << std::endl;
+  // collect free variables in all assertions
+  std::vector<Node> free_vars;
+  std::vector<TNode> visit;
+  std::unordered_set<TNode, TNodeHashFunction> visited;
+  for (const Node& as : assertions)
+  {
+    Trace("cbqi-gn") << "  " << as << std::endl;
+    TNode cur = as;
+    // compute free variables
+    visit.push_back(cur);
+    do
+    {
+      cur = visit.back();
+      visit.pop_back();
+      if (visited.find(cur) == visited.end())
+      {
+        visited.insert(cur);
+        if (cur.isVar() && cur.getKind() != BOUND_VARIABLE)
+        {
+          free_vars.push_back(cur);
+        }
+        for (const TNode& cn : cur)
+        {
+          visit.push_back(cn);
+        }
+      }
+    } while (!visit.empty());
+  }
+
+  Node body;
+  if (assertions.size() == 1)
+  {
+    body = assertions[0];
+  }
+  else
+  {
+    body = nm->mkNode(AND, assertions);
+  }
+
+  // do the negation
+  body = body.negate();
+
+  if (!free_vars.empty())
+  {
+    std::vector<Node> bvs;
+    for (const Node& v : free_vars)
+    {
+      Node bv = nm->mkBoundVar(v.getType());
+      bvs.push_back(bv);
+    }
+
+    body = body.substitute(
+        free_vars.begin(), free_vars.end(), bvs.begin(), bvs.end());
+
+    Node bvl = nm->mkNode(BOUND_VAR_LIST, bvs);
+
+    body = nm->mkNode(FORALL, bvl, body);
+  }
+
+  Trace("cbqi-gn-debug") << "...got (pre-rewrite) : " << body << std::endl;
+  body = Rewriter::rewrite(body);
+  Trace("cbqi-gn") << "...got (post-rewrite) : " << body << std::endl;
+  return body;
+}
+
+GlobalNegate::GlobalNegate(PreprocessingPassContext* preprocContext)
+    : PreprocessingPass(preprocContext, "global-negate"){};
+
+PreprocessingPassResult GlobalNegate::applyInternal(
+    AssertionPipeline* assertionsToPreprocess)
+{
+  NodeManager* nm = NodeManager::currentNM();
+  Node simplifiedNode = simplify(assertionsToPreprocess->ref(), nm);
+  Node trueNode = nm->mkConst(true);
+  for (unsigned i = 0; i < assertionsToPreprocess->size(); ++i)
+  {
+    assertionsToPreprocess->replace(i, trueNode);
+  }
+  assertionsToPreprocess->push_back(simplifiedNode);
+  return PreprocessingPassResult::NO_CONFLICT;
+}
+
+}  // namespace passes
+}  // namespace preprocessing
+}  // namespace CVC4
diff --git a/src/preprocessing/passes/global_negate.h b/src/preprocessing/passes/global_negate.h
new file mode 100644
index 000000000..0330aa10e
--- /dev/null
+++ b/src/preprocessing/passes/global_negate.h
@@ -0,0 +1,52 @@
+/*********************                                                        */
+/*! \file global_negate.h
+ ** \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 the global_negate preprocessing pass
+  * Updates a set of assertions to the negation of
+ * these assertions. In detail, if assertions is:
+ *    F1, ..., Fn
+ * then we update this vector to:
+ *    forall x1...xm. ~( F1 ^ ... ^ Fn ), true, ..., true
+ * where x1...xm are the free variables of F1...Fn.
+ * When this is done, d_globalNegation flag is marked, so that the solver checks
+ *for unsat instead of sat.
+**/
+
+#include "cvc4_private.h"
+
+#ifndef __CVC4__PREPROCESSING__PASSES__GLOBAL_NEGATE_H
+#define __CVC4__PREPROCESSING__PASSES__GLOBAL_NEGATE_H
+
+#include "preprocessing/preprocessing_pass.h"
+#include "preprocessing/preprocessing_pass_context.h"
+
+namespace CVC4 {
+namespace preprocessing {
+namespace passes {
+
+class GlobalNegate : public PreprocessingPass
+{
+ public:
+  GlobalNegate(PreprocessingPassContext* preprocContext);
+
+ protected:
+  PreprocessingPassResult applyInternal(
+      AssertionPipeline* assertionsToPreprocess) override;
+
+ private:
+  Node simplify(std::vector<Node>& assertions, NodeManager* nm);
+};
+
+}  // namespace passes
+}  // namespace preprocessing
+}  // namespace CVC4
+
+#endif /* __CVC4__PREPROCESSING_PASSES__GLOBAL_NEGATE_H */