Move current decision engine to decision engine old (#6466)

The decision engine is the class that contains strategies for doing e.g. justification heuristic.

The current implementation is hardcoded for the old implementation of justification heuristic.

Since both implementations will be maintained in the short term, this splits the parts of DecisionEngine that are specific to the old implementation to a class DecisionEngineOld.

It refactors the interface of DecisionEngine in a way that is compatible with both implementations.

9 files changed, 337 insertions, 174 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index af206c14d..901897e83 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -24,6 +24,8 @@ libcvc5_add_sources(
   decision/decision_attributes.h
   decision/decision_engine.cpp
   decision/decision_engine.h
+  decision/decision_engine_old.cpp
+  decision/decision_engine_old.h
   decision/decision_strategy.h
   decision/justification_heuristic.cpp
   decision/justification_heuristic.h
diff --git a/src/decision/decision_engine.cpp b/src/decision/decision_engine.cpp
index d55d2077f..4116ba90d 100644
--- a/src/decision/decision_engine.cpp
+++ b/src/decision/decision_engine.cpp
@@ -14,92 +14,80 @@
  */
 #include "decision/decision_engine.h"
 
-#include "decision/decision_attributes.h"
-#include "decision/justification_heuristic.h"
-#include "expr/node.h"
+#include "decision/decision_engine_old.h"
 #include "options/decision_options.h"
-#include "options/smt_options.h"
+#include "prop/sat_solver.h"
 #include "util/resource_manager.h"
 
-using namespace std;
-
 namespace cvc5 {
 namespace decision {
 
-DecisionEngine::DecisionEngine(context::Context* sc,
-                               context::UserContext* uc,
+DecisionEngine::DecisionEngine(context::Context* c,
+                               context::UserContext* u,
+                               prop::SkolemDefManager* skdm,
                                ResourceManager* rm)
-    : d_cnfStream(nullptr),
-      d_satSolver(nullptr),
-      d_satContext(sc),
-      d_userContext(uc),
-      d_result(sc, SAT_VALUE_UNKNOWN),
-      d_engineState(0),
+    : d_decEngineOld(new DecisionEngineOld(c, u)),
       d_resourceManager(rm),
-      d_enabledITEStrategy(nullptr)
+      d_useOld(true)
 {
-  Trace("decision") << "Creating decision engine" << std::endl;
 }
 
-void DecisionEngine::init()
+void DecisionEngine::finishInit(prop::CDCLTSatSolverInterface* ss,
+                                prop::CnfStream* cs)
 {
-  Assert(d_engineState == 0);
-  d_engineState = 1;
-
-  Trace("decision-init") << "DecisionEngine::init()" << std::endl;
-  Trace("decision-init") << " * options->decisionMode: "
-                         << options::decisionMode() << std:: endl;
-  Trace("decision-init") << " * options->decisionStopOnly: "
-                         << options::decisionStopOnly() << std::endl;
-
-  if (options::decisionMode() == options::DecisionMode::JUSTIFICATION)
+  if (d_useOld)
   {
-    d_enabledITEStrategy.reset(new decision::JustificationHeuristic(
-        this, d_userContext, d_satContext));
+    d_decEngineOld->setSatSolver(ss);
+    d_decEngineOld->setCnfStream(cs);
+    return;
   }
 }
 
-void DecisionEngine::shutdown()
-{
-  Trace("decision") << "Shutting down decision engine" << std::endl;
-
-  Assert(d_engineState == 1);
-  d_engineState = 2;
-  d_enabledITEStrategy.reset(nullptr);
-}
+void DecisionEngine::presolve() {}
 
-SatLiteral DecisionEngine::getNext(bool& stopSearch)
+prop::SatLiteral DecisionEngine::getNext(bool& stopSearch)
 {
   d_resourceManager->spendResource(Resource::DecisionStep);
-  Assert(d_cnfStream != nullptr)
-      << "Forgot to set cnfStream for decision engine?";
-  Assert(d_satSolver != nullptr)
-      << "Forgot to set satSolver for decision engine?";
+  if (d_useOld)
+  {
+    return d_decEngineOld->getNext(stopSearch);
+  }
+  return undefSatLiteral;
+}
 
-  return d_enabledITEStrategy == nullptr
-             ? undefSatLiteral
-             : d_enabledITEStrategy->getNext(stopSearch);
+bool DecisionEngine::isDone()
+{
+  if (d_useOld)
+  {
+    return d_decEngineOld->isDone();
+  }
+  return false;
 }
 
 void DecisionEngine::addAssertion(TNode assertion)
 {
-  // new assertions, reset whatever result we knew
-  d_result = SAT_VALUE_UNKNOWN;
-  if (d_enabledITEStrategy != nullptr)
+  if (d_useOld)
   {
-    d_enabledITEStrategy->addAssertion(assertion);
+    d_decEngineOld->addAssertion(assertion);
+    return;
   }
 }
 
 void DecisionEngine::addSkolemDefinition(TNode lem, TNode skolem)
 {
-  // new assertions, reset whatever result we knew
-  d_result = SAT_VALUE_UNKNOWN;
-  if (d_enabledITEStrategy != nullptr)
+  if (d_useOld)
   {
-    d_enabledITEStrategy->addSkolemDefinition(lem, skolem);
+    d_decEngineOld->addSkolemDefinition(lem, skolem);
   }
 }
 
+void DecisionEngine::notifyAsserted(TNode n)
+{
+  if (d_useOld)
+  {
+    return;
+  }
 }
+
+}  // namespace decision
 }  // namespace cvc5
diff --git a/src/decision/decision_engine.h b/src/decision/decision_engine.h
index c10fe2bb9..de88d656e 100644
--- a/src/decision/decision_engine.h
+++ b/src/decision/decision_engine.h
@@ -18,110 +18,41 @@
 #ifndef CVC5__DECISION__DECISION_ENGINE_H
 #define CVC5__DECISION__DECISION_ENGINE_H
 
-#include "base/output.h"
-#include "context/cdo.h"
-#include "decision/decision_strategy.h"
 #include "expr/node.h"
 #include "prop/cnf_stream.h"
 #include "prop/sat_solver.h"
 #include "prop/sat_solver_types.h"
-#include "util/result.h"
-
-using namespace cvc5::prop;
-using namespace cvc5::decision;
 
 namespace cvc5 {
-namespace decision {
-
-class DecisionEngine {
-
-  // PropEngine* d_propEngine;
-  CnfStream* d_cnfStream;
-  CDCLTSatSolverInterface* d_satSolver;
-
-  context::Context* d_satContext;
-  context::UserContext* d_userContext;
 
-  // Does decision engine know the answer?
-  context::CDO<SatValue> d_result;
+namespace prop {
+class SkolemDefManager;
+}
 
-  // Disable creating decision engine without required parameters
-  DecisionEngine();
+class DecisionEngineOld;
 
-  // init/shutdown state
-  unsigned d_engineState;    // 0=pre-init; 1=init,pre-shutdown; 2=shutdown
-  /** Pointer to resource manager for associated SmtEngine */
-  ResourceManager* d_resourceManager;
+namespace decision {
 
+class DecisionEngine
+{
  public:
-  // Necessary functions
-
   /** Constructor */
   DecisionEngine(context::Context* sc,
                  context::UserContext* uc,
+                 prop::SkolemDefManager* skdm,
                  ResourceManager* rm);
 
-  /** Destructor, currently does nothing */
-  ~DecisionEngine() {
-    Trace("decision") << "Destroying decision engine" << std::endl;
-  }
-
-  void setSatSolver(CDCLTSatSolverInterface* ss)
-  {
-    // setPropEngine should not be called more than once
-    Assert(d_satSolver == NULL);
-    Assert(ss != NULL);
-    d_satSolver = ss;
-  }
-
-  void setCnfStream(CnfStream* cs) {
-    // setPropEngine should not be called more than once
-    Assert(d_cnfStream == NULL);
-    Assert(cs != NULL);
-    d_cnfStream = cs;
-  }
-
-  /* Enables decision strategy based on options. */
-  void init();
+  /** Finish initialize */
+  void finishInit(prop::CDCLTSatSolverInterface* ss, prop::CnfStream* cs);
 
-  /**
-   * This is called by SmtEngine, at shutdown time, just before
-   * destruction.  It is important because there are destruction
-   * ordering issues between some parts of the system.
-   */
-  void shutdown();
-
-  // Interface for External World to use our services
+  /** Presolve, called at the beginning of each check-sat call */
+  void presolve();
 
   /** Gets the next decision based on strategies that are enabled */
-  SatLiteral getNext(bool& stopSearch);
+  prop::SatLiteral getNext(bool& stopSearch);
 
   /** Is the DecisionEngine in a state where it has solved everything? */
-  bool isDone() {
-    Trace("decision") << "DecisionEngine::isDone() returning "
-                      << (d_result != SAT_VALUE_UNKNOWN)
-                      << (d_result != SAT_VALUE_UNKNOWN ? "true" : "false")
-                      << std::endl;
-    return (d_result != SAT_VALUE_UNKNOWN);
-  }
-
-  /** */
-  Result getResult() {
-    switch(d_result.get()) {
-    case SAT_VALUE_TRUE: return Result(Result::SAT);
-    case SAT_VALUE_FALSE: return Result(Result::UNSAT);
-    case SAT_VALUE_UNKNOWN: return Result(Result::SAT_UNKNOWN, Result::UNKNOWN_REASON);
-    default: Assert(false) << "d_result is garbage";
-    }
-    return Result();
-  }
-
-  /** */
-  void setResult(SatValue val) {
-    d_result = val;
-  }
-
-  // External World helping us help the Strategies
+  bool isDone();
 
   /**
    * Notify this class that assertion is an (input) assertion, not corresponding
@@ -129,38 +60,27 @@ class DecisionEngine {
    */
   void addAssertion(TNode assertion);
   /**
+   * TODO: remove this interface
    * Notify this class  that lem is the skolem definition for skolem, which is
    * a part of the current assertions.
    */
   void addSkolemDefinition(TNode lem, TNode skolem);
-
-  // Interface for Strategies to use stuff stored in Decision Engine
-  // (which was possibly requested by them on initialization)
-
-  // Interface for Strategies to get information about External World
-
-  bool hasSatLiteral(TNode n) {
-    return d_cnfStream->hasLiteral(n);
-  }
-  SatLiteral getSatLiteral(TNode n) {
-    return d_cnfStream->getLiteral(n);
-  }
-  SatValue getSatValue(SatLiteral l) {
-    return d_satSolver->value(l);
-  }
-  SatValue getSatValue(TNode n) {
-    return getSatValue(getSatLiteral(n));
-  }
-  Node getNode(SatLiteral l) {
-    return d_cnfStream->getNode(l);
-  }
+  /**
+   * Notify this class that the literal n has been asserted, possibly
+   * propagated by the SAT solver.
+   */
+  void notifyAsserted(TNode n);
 
  private:
-  /** The ITE decision strategy we have allocated */
-  std::unique_ptr<ITEDecisionStrategy> d_enabledITEStrategy;
-};/* DecisionEngine class */
+  /** The old implementation */
+  std::unique_ptr<DecisionEngineOld> d_decEngineOld;
+  /** Pointer to resource manager for associated SmtEngine */
+  ResourceManager* d_resourceManager;
+  /** using old implementation? */
+  bool d_useOld;
+};
 
-}
+}  // namespace decision
 }  // namespace cvc5
 
 #endif /* CVC5__DECISION__DECISION_ENGINE_H */
diff --git a/src/decision/decision_engine_old.cpp b/src/decision/decision_engine_old.cpp
new file mode 100644
index 000000000..8ef7ad1f4
--- /dev/null
+++ b/src/decision/decision_engine_old.cpp
@@ -0,0 +1,96 @@
+/******************************************************************************
+ * Top contributors (to current version):
+ *   Kshitij Bansal, Aina Niemetz, Andrew Reynolds
+ *
+ * This file is part of the cvc5 project.
+ *
+ * Copyright (c) 2009-2021 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.
+ * ****************************************************************************
+ *
+ * Old implementation of the decision engine
+ */
+#include "decision/decision_engine_old.h"
+
+#include "decision/decision_attributes.h"
+#include "decision/justification_heuristic.h"
+#include "expr/node.h"
+#include "options/decision_options.h"
+#include "options/smt_options.h"
+#include "util/resource_manager.h"
+
+using namespace std;
+
+namespace cvc5 {
+
+DecisionEngineOld::DecisionEngineOld(context::Context* sc,
+                                     context::UserContext* uc)
+    : d_cnfStream(nullptr),
+      d_satSolver(nullptr),
+      d_satContext(sc),
+      d_userContext(uc),
+      d_result(sc, SAT_VALUE_UNKNOWN),
+      d_engineState(0),
+      d_enabledITEStrategy(nullptr)
+{
+  Trace("decision") << "Creating decision engine" << std::endl;
+  Assert(d_engineState == 0);
+  d_engineState = 1;
+
+  Trace("decision-init") << "DecisionEngineOld::init()" << std::endl;
+  Trace("decision-init") << " * options->decisionMode: "
+                         << options::decisionMode() << std::endl;
+  Trace("decision-init") << " * options->decisionStopOnly: "
+                         << options::decisionStopOnly() << std::endl;
+
+  if (options::decisionMode() == options::DecisionMode::JUSTIFICATION)
+  {
+    d_enabledITEStrategy.reset(new decision::JustificationHeuristic(
+        this, d_userContext, d_satContext));
+  }
+}
+
+void DecisionEngineOld::shutdown()
+{
+  Trace("decision") << "Shutting down decision engine" << std::endl;
+
+  Assert(d_engineState == 1);
+  d_engineState = 2;
+  d_enabledITEStrategy.reset(nullptr);
+}
+
+SatLiteral DecisionEngineOld::getNext(bool& stopSearch)
+{
+  Assert(d_cnfStream != nullptr)
+      << "Forgot to set cnfStream for decision engine?";
+  Assert(d_satSolver != nullptr)
+      << "Forgot to set satSolver for decision engine?";
+
+  return d_enabledITEStrategy == nullptr
+             ? undefSatLiteral
+             : d_enabledITEStrategy->getNext(stopSearch);
+}
+
+void DecisionEngineOld::addAssertion(TNode assertion)
+{
+  // new assertions, reset whatever result we knew
+  d_result = SAT_VALUE_UNKNOWN;
+  if (d_enabledITEStrategy != nullptr)
+  {
+    d_enabledITEStrategy->addAssertion(assertion);
+  }
+}
+
+void DecisionEngineOld::addSkolemDefinition(TNode lem, TNode skolem)
+{
+  // new assertions, reset whatever result we knew
+  d_result = SAT_VALUE_UNKNOWN;
+  if (d_enabledITEStrategy != nullptr)
+  {
+    d_enabledITEStrategy->addSkolemDefinition(lem, skolem);
+  }
+}
+
+}  // namespace cvc5
diff --git a/src/decision/decision_engine_old.h b/src/decision/decision_engine_old.h
new file mode 100644
index 000000000..e9169d9b2
--- /dev/null
+++ b/src/decision/decision_engine_old.h
@@ -0,0 +1,150 @@
+/******************************************************************************
+ * Top contributors (to current version):
+ *   Kshitij Bansal, Andrew Reynolds, Morgan Deters
+ *
+ * This file is part of the cvc5 project.
+ *
+ * Copyright (c) 2009-2021 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.
+ * ****************************************************************************
+ *
+ * Old implementation of the decision engine
+ */
+
+#include "cvc5_private.h"
+
+#ifndef CVC4__DECISION__DECISION_ENGINE_OLD_H
+#define CVC4__DECISION__DECISION_ENGINE_OLD_H
+
+#include "base/output.h"
+#include "context/cdo.h"
+#include "decision/decision_strategy.h"
+#include "expr/node.h"
+#include "prop/cnf_stream.h"
+#include "prop/sat_solver.h"
+#include "prop/sat_solver_types.h"
+#include "util/result.h"
+
+using namespace cvc5::prop;
+using namespace cvc5::decision;
+
+namespace cvc5 {
+
+class DecisionEngineOld
+{
+ public:
+  // Necessary functions
+
+  /** Constructor */
+  DecisionEngineOld(context::Context* sc, context::UserContext* uc);
+
+  /** Destructor, currently does nothing */
+  ~DecisionEngineOld()
+  {
+    Trace("decision") << "Destroying decision engine" << std::endl;
+  }
+
+  void setSatSolver(CDCLTSatSolverInterface* ss)
+  {
+    // setPropEngine should not be called more than once
+    Assert(d_satSolver == NULL);
+    Assert(ss != NULL);
+    d_satSolver = ss;
+  }
+
+  void setCnfStream(CnfStream* cs)
+  {
+    // setPropEngine should not be called more than once
+    Assert(d_cnfStream == NULL);
+    Assert(cs != NULL);
+    d_cnfStream = cs;
+  }
+
+  /**
+   * This is called by SmtEngine, at shutdown time, just before
+   * destruction.  It is important because there are destruction
+   * ordering issues between some parts of the system.
+   */
+  void shutdown();
+
+  // Interface for External World to use our services
+
+  /** Gets the next decision based on strategies that are enabled */
+  SatLiteral getNext(bool& stopSearch);
+
+  /** Is the DecisionEngineOld in a state where it has solved everything? */
+  bool isDone()
+  {
+    Trace("decision") << "DecisionEngineOld::isDone() returning "
+                      << (d_result != SAT_VALUE_UNKNOWN)
+                      << (d_result != SAT_VALUE_UNKNOWN ? "true" : "false")
+                      << std::endl;
+    return (d_result != SAT_VALUE_UNKNOWN);
+  }
+
+  /** */
+  Result getResult()
+  {
+    switch (d_result.get())
+    {
+      case SAT_VALUE_TRUE: return Result(Result::SAT);
+      case SAT_VALUE_FALSE: return Result(Result::UNSAT);
+      case SAT_VALUE_UNKNOWN:
+        return Result(Result::SAT_UNKNOWN, Result::UNKNOWN_REASON);
+      default: Assert(false) << "d_result is garbage";
+    }
+    return Result();
+  }
+
+  /** */
+  void setResult(SatValue val) { d_result = val; }
+
+  // External World helping us help the Strategies
+
+  /**
+   * Notify this class that assertion is an (input) assertion, not corresponding
+   * to a skolem definition.
+   */
+  void addAssertion(TNode assertion);
+  /**
+   * Notify this class  that lem is the skolem definition for skolem, which is
+   * a part of the current assertions.
+   */
+  void addSkolemDefinition(TNode lem, TNode skolem);
+
+  // Interface for Strategies to use stuff stored in Decision Engine
+  // (which was possibly requested by them on initialization)
+
+  // Interface for Strategies to get information about External World
+
+  bool hasSatLiteral(TNode n) { return d_cnfStream->hasLiteral(n); }
+  SatLiteral getSatLiteral(TNode n) { return d_cnfStream->getLiteral(n); }
+  SatValue getSatValue(SatLiteral l) { return d_satSolver->value(l); }
+  SatValue getSatValue(TNode n) { return getSatValue(getSatLiteral(n)); }
+  Node getNode(SatLiteral l) { return d_cnfStream->getNode(l); }
+
+ private:
+  // Disable creating decision engine without required parameters
+  DecisionEngineOld();
+
+  CnfStream* d_cnfStream;
+  CDCLTSatSolverInterface* d_satSolver;
+
+  context::Context* d_satContext;
+  context::UserContext* d_userContext;
+
+  // Does decision engine know the answer?
+  context::CDO<SatValue> d_result;
+
+  // init/shutdown state
+  unsigned d_engineState;  // 0=pre-init; 1=init,pre-shutdown; 2=shutdown
+  /** The ITE decision strategy we have allocated */
+  std::unique_ptr<ITEDecisionStrategy> d_enabledITEStrategy;
+
+}; /* DecisionEngineOld class */
+
+}  // namespace cvc5
+
+#endif /* CVC4__DECISION__DECISION_ENGINE_H */
diff --git a/src/decision/decision_strategy.h b/src/decision/decision_strategy.h
index 0376b00cc..87c463c29 100644
--- a/src/decision/decision_strategy.h
+++ b/src/decision/decision_strategy.h
@@ -26,6 +26,8 @@
 
 namespace cvc5 {
 
+class DecisionEngineOld;
+
 namespace context {
   class Context;
   }  // namespace context
@@ -36,10 +38,12 @@ class DecisionEngine;
 
 class DecisionStrategy {
 protected:
-  DecisionEngine* d_decisionEngine;
+ DecisionEngineOld* d_decisionEngine;
+
 public:
-  DecisionStrategy(DecisionEngine* de, context::Context *c) :
-    d_decisionEngine(de) {
+ DecisionStrategy(DecisionEngineOld* de, context::Context* c)
+     : d_decisionEngine(de)
+ {
   }
 
   virtual ~DecisionStrategy() { }
@@ -49,8 +53,9 @@ public:
 
 class ITEDecisionStrategy : public DecisionStrategy {
 public:
-  ITEDecisionStrategy(DecisionEngine* de, context::Context *c) :
-    DecisionStrategy(de, c) {
+ ITEDecisionStrategy(DecisionEngineOld* de, context::Context* c)
+     : DecisionStrategy(de, c)
+ {
   }
   /**
    * Add that assertion is an (input) assertion, not corresponding to a
diff --git a/src/decision/justification_heuristic.cpp b/src/decision/justification_heuristic.cpp
index ecc0ae68c..dcf8975bb 100644
--- a/src/decision/justification_heuristic.cpp
+++ b/src/decision/justification_heuristic.cpp
@@ -20,7 +20,7 @@
 #include "justification_heuristic.h"
 
 #include "decision/decision_attributes.h"
-#include "decision/decision_engine.h"
+#include "decision/decision_engine_old.h"
 #include "expr/kind.h"
 #include "expr/node_manager.h"
 #include "options/decision_options.h"
@@ -29,10 +29,12 @@
 #include "theory/rewriter.h"
 #include "util/random.h"
 
+using namespace cvc5::prop;
+
 namespace cvc5 {
 namespace decision {
 
-JustificationHeuristic::JustificationHeuristic(DecisionEngine* de,
+JustificationHeuristic::JustificationHeuristic(DecisionEngineOld* de,
                                                context::UserContext* uc,
                                                context::Context* c)
     : ITEDecisionStrategy(de, c),
diff --git a/src/decision/justification_heuristic.h b/src/decision/justification_heuristic.h
index 45f297bb9..870d0674c 100644
--- a/src/decision/justification_heuristic.h
+++ b/src/decision/justification_heuristic.h
@@ -117,7 +117,7 @@ class JustificationHeuristic : public ITEDecisionStrategy {
   };
 
 public:
- JustificationHeuristic(DecisionEngine* de,
+ JustificationHeuristic(DecisionEngineOld* de,
                         context::UserContext* uc,
                         context::Context* c);
 
diff --git a/src/prop/prop_engine.cpp b/src/prop/prop_engine.cpp
index dfd4c4528..70401c56d 100644
--- a/src/prop/prop_engine.cpp
+++ b/src/prop/prop_engine.cpp
@@ -22,6 +22,7 @@
 #include "base/check.h"
 #include "base/output.h"
 #include "decision/decision_engine.h"
+#include "decision/decision_engine_old.h"
 #include "options/base_options.h"
 #include "options/decision_options.h"
 #include "options/main_options.h"
@@ -88,8 +89,8 @@ PropEngine::PropEngine(TheoryEngine* te,
   context::UserContext* userContext = d_env.getUserContext();
   ResourceManager* rm = d_env.getResourceManager();
 
-  d_decisionEngine.reset(new DecisionEngine(satContext, userContext, rm));
-  d_decisionEngine->init();  // enable appropriate strategies
+  d_decisionEngine.reset(
+      new decision::DecisionEngine(satContext, userContext, d_skdm.get(), rm));
 
   d_satSolver = SatSolverFactory::createCDCLTMinisat(smtStatisticsRegistry());
 
@@ -120,8 +121,7 @@ PropEngine::PropEngine(TheoryEngine* te,
           ? pnm
           : nullptr);
 
-  d_decisionEngine->setSatSolver(d_satSolver);
-  d_decisionEngine->setCnfStream(d_cnfStream);
+  d_decisionEngine->finishInit(d_satSolver, d_cnfStream);
   if (pnm && options::unsatCoresMode() != options::UnsatCoresMode::ASSUMPTIONS)
   {
     d_pfCnfStream.reset(new ProofCnfStream(
@@ -157,7 +157,6 @@ void PropEngine::finishInit()
 
 PropEngine::~PropEngine() {
   Debug("prop") << "Destructing the PropEngine" << std::endl;
-  d_decisionEngine->shutdown();
   d_decisionEngine.reset(nullptr);
   delete d_cnfStream;
   delete d_satSolver;
@@ -370,6 +369,7 @@ Result PropEngine::checkSat() {
   d_inCheckSat = true;
 
   // TODO This currently ignores conflicts (a dangerous practice).
+  d_decisionEngine->presolve();
   d_theoryEngine->presolve();
 
   if(options::preprocessOnly()) {