search_fast.cpp

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00001 ///////////////////////////////////////////////////////////////////////////////
00002 /*!
00003  * \file search_fast.cpp
00004  *
00005  * Author: Mark Zavislak <zavislak@stanford.edu>
00006  *         Undergraduate
00007  *         Stanford University          
00008  *
00009  * Created: Mon Jul 21 23:52:39 UTC 2003
00010  *
00011  * <hr>
00012  *
00013  * License to use, copy, modify, sell and/or distribute this software
00014  * and its documentation for any purpose is hereby granted without
00015  * royalty, subject to the terms and conditions defined in the \ref
00016  * LICENSE file provided with this distribution.
00017  * 
00018  * <hr>
00019 */
00020 ///////////////////////////////////////////////////////////////////////////////
00021 
00022 #include "search_fast.h"
00023 #include "typecheck_exception.h"
00024 #include "search_rules.h"
00025 #include "command_line_flags.h"
00026 #include "cdmap.h"
00027 #include "decision_engine_dfs.h"
00028 //#include "decision_engine_caching.h"
00029 //#include "decision_engine_mbtf.h"
00030 #include "expr_transform.h"
00031 #include "assumptions.h"
00032 
00033 
00034 using namespace CVC3;
00035 using namespace std;
00036 
00037 
00038 //! When set to true, match Chaff behavior as close as possible
00039 #define followChaff false
00040 
00041 
00042 void SearchEngineFast::ConflictClauseManager::setRestorePoint()
00043 {
00044   TRACE("conflict clauses",
00045   "ConflictClauseManager::setRestorePoint(): scope=",
00046       d_se->scopeLevel(), "");
00047   d_se->d_conflictClauseStack.push_back(new deque<ClauseOwner>());
00048   d_se->d_conflictClauses = d_se->d_conflictClauseStack.back();
00049   d_restorePoints.push_back(d_se->scopeLevel());
00050 }
00051 
00052 
00053 void SearchEngineFast::ConflictClauseManager::notify()
00054 {
00055   if (d_restorePoints.size() > 0) {
00056     int scope = d_restorePoints.back();
00057     if (scope > d_se->scopeLevel()) {
00058       TRACE("conflict clauses",
00059       "ConflictClauseManager::notify(): restore to scope ", scope, "");
00060       d_restorePoints.pop_back();
00061       while (d_se->d_conflictClauses->size() > 0)
00062         d_se->d_conflictClauses->pop_back();
00063       delete d_se->d_conflictClauseStack.back();
00064       d_se->d_conflictClauseStack.pop_back();
00065       d_se->d_conflictClauses = d_se->d_conflictClauseStack.back();
00066     }
00067   }
00068 }
00069 
00070 
00071 //! Constructor
00072 SearchEngineFast::SearchEngineFast(TheoryCore* core)
00073   : SearchImplBase(core),
00074     d_name("fast"),
00075     d_unitPropCount(core->getStatistics().counter("unit propagations")),
00076     d_circuitPropCount(core->getStatistics().counter("circuit propagations")),
00077     d_conflictCount(core->getStatistics().counter("conflicts")),
00078     d_conflictClauseCount(core->getStatistics().counter("conflict clauses")),
00079     d_clauses(core->getCM()->getCurrentContext()),
00080     d_unreportedLits(core->getCM()->getCurrentContext()),
00081     d_unreportedLitsHandled(core->getCM()->getCurrentContext()),
00082     d_nonLiterals(core->getCM()->getCurrentContext()),
00083     d_nonLiteralsSaved(core->getCM()->getCurrentContext()),
00084     d_simplifiedThm(core->getCM()->getCurrentContext()),
00085     d_nonlitQueryStart(core->getCM()->getCurrentContext()),
00086     d_nonlitQueryEnd(core->getCM()->getCurrentContext()),
00087     d_clausesQueryStart(core->getCM()->getCurrentContext()),
00088     d_clausesQueryEnd(core->getCM()->getCurrentContext()),
00089     d_conflictClauseManager(core->getCM()->getCurrentContext(), this),
00090     d_literalSet(core->getCM()->getCurrentContext()),
00091     d_useEnqueueFact(false),
00092     d_inCheckSAT(false),
00093     d_litsAlive(core->getCM()->getCurrentContext()),
00094     d_litsMaxScorePos(0),
00095     d_splitterCount(0),
00096     d_litSortCount(0),
00097     d_berkminFlag(false)
00098 {
00099 //   if (core->getFlags()["de"].getString() == "caching")
00100 //     d_decisionEngine = new DecisionEngineCaching(core, this);
00101 //   else if (core->getFlags()["de"].getString() == "mbtf")
00102 //     d_decisionEngine = new DecisionEngineMBTF(core, this);
00103 //   else
00104     d_decisionEngine = new DecisionEngineDFS(core, this);
00105 
00106   IF_DEBUG (
00107     d_nonLiterals.setName("CDList[SearchEngineDefault.d_nonLiterals]");
00108     d_clauses.setName("CDList[SearchEngineDefault.d_clauses]");
00109   )
00110 
00111   d_conflictClauseStack.push_back(new deque<ClauseOwner>());
00112   d_conflictClauses = d_conflictClauseStack.back();
00113 }
00114 
00115 //! Destructor
00116 /*! We own the proof rules (d_rules) and the variable manager (d_vm);
00117   delete them. */
00118 SearchEngineFast::~SearchEngineFast() {
00119   for (unsigned i=0; i < d_circuits.size(); i++)
00120     delete d_circuits[i];
00121   delete d_decisionEngine;
00122   for(size_t i=0, iend=d_conflictClauseStack.size(); i<iend; ++i)
00123     delete d_conflictClauseStack[i];
00124 }
00125 
00126 
00127 /*! @brief Return a ref to the vector of watched literals.  If no
00128   such vector exists, create it. */
00129 /*!  This function is normally used when the value of 'literal'
00130  * becomes false.  The vector contains pointers to all clauses where
00131  * this literal occurs, and therefore, these clauses may cause unit
00132  * propagation.  In any case, the watch pointers in these clauses
00133  * need to be updated.
00134  */
00135 vector<std::pair<Clause, int> >& 
00136 SearchEngineFast::wp(const Literal& literal) {
00137   // return d_wp[literal.getExpr()];
00138   return literal.wp();
00139 }
00140 
00141 #ifdef _CVC3_DEBUG_MODE
00142 static void checkAssump(const Theorem& t, const Theorem& orig,
00143      const CDMap<Expr,Theorem>& assumptions) {
00144   const Assumptions& a(t.getAssumptionsRef());
00145   const Assumptions::iterator iend = a.end();
00146   if(!(!t.isAssump() || assumptions.count(t.getExpr()) > 0))
00147     orig.printDebug();
00148   DebugAssert((!t.isAssump() || assumptions.count(t.getExpr()) > 0), 
00149         "checkAssump: found stray theorem:\n  "
00150         + t.toString());
00151   if(t.isAssump()) return;
00152   for (Assumptions::iterator i = a.begin(); i != iend; ++i) {
00153     if (!i->isFlagged()) {
00154       i->setFlag();
00155       // comparing only TheoremValue pointers in .find()
00156       checkAssump(*i, orig, assumptions);
00157     }
00158   }
00159 }
00160 
00161 
00162 /*! @brief Check that assumptions in the result of checkValid() are a
00163   subset of assertions */
00164 /*! Only defined in the debug build. 
00165  * \ingroup SE_Default
00166  */
00167 static void
00168 checkAssumpDebug(const Theorem& res,
00169      const CDMap<Expr,Theorem>& assumptions) {
00170   // FIXME: (jimz) will need to traverse graph
00171 
00172   if(!res.withAssumptions()) return;
00173   res.clearAllFlags();
00174   checkAssump(res, res, assumptions);
00175 }
00176 #endif
00177 
00178 
00179 
00180 
00181 ////////////////////////////
00182 // New Search Engine Code //
00183 ////////////////////////////
00184 
00185 
00186 QueryResult SearchEngineFast::checkSAT()
00187 {
00188   d_inCheckSAT=true;
00189   QueryResult result = UNSATISFIABLE;
00190   if (!bcp()) { // run an initial bcp
00191     DebugAssert(d_factQueue.empty(), "checkSAT()");
00192     if (!fixConflict()) goto checkSATfinalize;
00193   }
00194   while (!d_core->outOfResources()) {
00195     if (split()) {   // if we were able to split successfully
00196       // Run BCP
00197       while (!bcp()) {  // while bcp finds conflicts
00198   DebugAssert(d_factQueue.empty(), "checkSAT()");
00199   d_decisionEngine->goalSatisfied();
00200 
00201         // Try to fix those conflicts by rolling back contexts and
00202         // adding new conflict clauses to help in the future.
00203         if (!fixConflict()) goto checkSATfinalize;
00204       }
00205     }
00206     // Now we couldn't find a splitter.  This may have been caused by
00207     // other reasons, so we allow them to be processed here.
00208     else {
00209       result = SATISFIABLE;
00210       break;
00211     }
00212   }
00213  checkSATfinalize:
00214   d_inCheckSAT = false;
00215   if (d_core->outOfResources()) result = ABORT;
00216   else if (result == SATISFIABLE && d_core->incomplete()) result = UNKNOWN;
00217   return result;
00218 }
00219 
00220 
00221 /* There are different heurisitics for splitters available.  We would
00222  * normally try to use the new generic decision class, but initially
00223  * we want this just to work, and so we use a custom decision class
00224  * that knows about this particular search engine.  We can realize
00225  * this same behavior using the existing mechanism by having a
00226  * decision subclass dynamic_cast the received SearchEngine pointer as
00227  * a SearchEngineFast and work from there.  However, as of this time I
00228  * do not plan on supporting the nextClause() and nextNonClause()
00229  * functionality, as they don't make much sense in this kind of modern
00230  * solver.  It may make more sense to have the solver and it's literal
00231  * splitting heuristic tightly connected, but leaving the nonLiteral
00232  * splitting heurisitic separate, since it is generally independent of
00233  * the search mechanism.
00234  *
00235  * By this point we've already guaranteed that we need to split: no
00236  * unit clauses, and no conflicts.  The procedure is as follows.  Ask
00237  * the decision engine for an expression to split on.  The decision
00238  * engine dutifully returns an expression.  We craft an assumption out
00239  * of this and assert it to the core (after making sure d_assumptions
00240  * has a copy).
00241  *
00242  * If no splitters are available, we still have to let the decision
00243  * procedures have a final chance at showing the context is
00244  * inconsistent by calling checkSATcore().  If we get a false out of
00245  * this, we have to continue processing, so the context is left
00246  * unchanged, no splitter is chosen, and we return true to let the
00247  * bcp+conflict processing have another chance.  If we get true, then
00248  * the problem is SAT and we are done, so we return false.
00249  *
00250  * Otherwise, we obtain the splitter, then ship it back off to the
00251  * decision engine for processing.
00252  */
00253 
00254 bool SearchEngineFast::split()
00255 {
00256   TRACE_MSG("search basic", "Choosing splitter");
00257   Expr splitter = findSplitter();
00258   if (splitter.isNull()) {
00259     TRACE_MSG("search basic", "No splitter");
00260     bool res(d_core->inconsistent() || !d_core->checkSATCore());
00261     if(!res) {
00262       d_splitterCount = 0; // Force resorting splitters next time
00263       res = !bcp();
00264     }
00265     return res;
00266   }
00267   Literal l(newLiteral(splitter));
00268   Theorem simp;
00269   if(l.getValue() != 0) {
00270     // The literal is valid at a lower scope than it has been derived,
00271     // and therefore, it was lost after a scope pop.  Reassert it here.
00272     simp = l.deriveTheorem();
00273     d_literals.push_back((l.getValue() == 1)? l : !l);
00274     d_core->addFact(simp);
00275     return true;
00276   }
00277   else {
00278     simp = d_core->simplify(splitter);
00279     Expr e = simp.getRHS();
00280     if(e.isBoolConst()) {
00281       IF_DEBUG(debugger.counter("splitter simplified to TRUE or FALSE")++;)
00282       if(e.isTrue()) simp = d_commonRules->iffTrueElim(simp);
00283       else {
00284   if(splitter.isNot())
00285     simp = d_commonRules->notNotElim(d_commonRules->iffFalseElim(simp));
00286   else
00287     simp = d_commonRules->iffFalseElim(simp);
00288       }
00289       TRACE("search full", "Simplified candidate: ", splitter.toString(), "");
00290       TRACE("search full", "                  to: ",
00291       simp.getExpr().toString(), "");
00292       // Send this literal to DPs and enqueue it for BCP
00293       d_core->addFact(simp);
00294       addLiteralFact(simp);
00295       DebugAssert(l.getValue()!=0, "SearchFast::split(): l = "+l.toString());
00296       return true;
00297     }
00298   }
00299 
00300   TRACE("search terse", "Asserting splitter: #"
00301   +int2string(d_core->getStatistics().counter("splitters"))+": ",
00302   splitter, "");
00303   d_decisionEngine->pushDecision(splitter);
00304   return true;
00305 }
00306 
00307 //! Total order on literals for the initial sort
00308 /*! Used for debugging, to match Chaff's behavior as close as possible
00309   and track any discrepancies or inefficiencies. */
00310 // static bool compareInitial(const Literal& l1, const Literal& l2) {
00311 //   Expr lit1 = l1.getVar().getExpr();
00312 //   Expr lit2 = l2.getVar().getExpr();
00313 //   if(lit1.hasOp() && lit2.hasOp()) {
00314 //     int i = atoi(&(lit1.getOp().getName().c_str()[2]));
00315 //     int j = atoi(&(lit2.getOp().getName().c_str()[2]));
00316 //     return (i < j);
00317 //   }
00318 //   else
00319 //     return (l1.score() > l2.score());
00320 // }
00321 
00322 //! Ordering on literals, used to sort them by score
00323 static inline bool compareLits(const Literal& l1, 
00324              const Literal& l2) 
00325 {
00326   return (l1.score() > l2.score());
00327 }
00328 
00329 IF_DEBUG(static string lits2str(const vector<Literal>& lits) {
00330   ostringstream ss;
00331   ss << "\n[";
00332   for(vector<Literal>::const_iterator i=lits.begin(), iend=lits.end();
00333       i!=iend; ++i)
00334     ss << *i << "\n ";
00335   ss << "\n]";
00336   return ss.str();
00337 })
00338 
00339 
00340 /*!
00341  * Recompute the scores for all known literals.  This is a relatively
00342  * expensive procedure, so it should not be called too often.
00343  * Currently, it is called once per 100 splitters.
00344  */
00345 void SearchEngineFast::updateLitScores(bool firstTime)
00346 {
00347   TRACE("search literals", "updateLitScores(size=", d_litsByScores.size(),
00348   ") {");
00349   unsigned count, score;
00350 
00351   if (firstTime && followChaff) {
00352     ::stable_sort(d_litsByScores.begin(), d_litsByScores.end(), compareLits);
00353   }
00354 
00355   for(size_t i=0; i< d_litsByScores.size(); ++i) {
00356     // Reading by value, since we'll be modifying the attributes.
00357     Literal lit = d_litsByScores[i];
00358     // First, clean up the unused literals
00359     while(lit.count()==0 && i+1 < d_litsByScores.size()) {
00360       TRACE("search literals", "Removing lit["+int2string(i)+"] = ", lit,
00361       " from d_litsByScores");
00362       // Remove this literal from the list
00363       lit.added()=false;
00364       lit = d_litsByScores.back();
00365       d_litsByScores[i] = lit;
00366       d_litsByScores.pop_back();
00367     }
00368     // Take care of the last literal in the vector
00369     if(lit.count()==0 && i+1 == d_litsByScores.size()) {
00370       TRACE("search literals", "Removing last lit["+int2string(i)+"] = ", lit,
00371       " from d_litsByScores");
00372       lit.added()=false;
00373       d_litsByScores.pop_back();
00374       break; // Break out of the loop -- no more literals to process
00375     }
00376 
00377     TRACE("search literals", "Updating lit["+int2string(i)+"] = ", lit, " {");
00378 
00379     DebugAssert(lit == d_litsByScores[i], "lit = "+lit.toString());
00380     DebugAssert(lit.added(), "lit = "+lit.toString());
00381     DebugAssert(lit.count()>0, "lit = "+lit.toString());
00382 
00383     count = lit.count();
00384     unsigned& countPrev = lit.countPrev();
00385     int& scoreRef = lit.score();
00386 
00387     score = scoreRef/2 + count - countPrev;
00388     scoreRef = score;
00389     countPrev = count;
00390 
00391     TRACE("search literals", "Updated lit["+int2string(i)+"] = ", lit, " }");
00392 //     Literal neglit(!lit);
00393 
00394 //     count = neglit.count();
00395 //     unsigned& negcountPrev = neglit.countPrev();
00396 //     unsigned& negscoreRef = neglit.score();
00397 
00398 //     negscore = negscoreRef/2 + count - negcountPrev;
00399 //     negscoreRef = negscore;
00400 //     negcountPrev = count;
00401 
00402 //     if(negscore > score) d_litsByScores[i] = neglit;
00403   }
00404   ::stable_sort(d_litsByScores.begin(), d_litsByScores.end(), compareLits);
00405   d_litsMaxScorePos = 0;
00406   d_litSortCount=d_litsByScores.size();
00407   TRACE("search splitters","updateLitScores => ", lits2str(d_litsByScores),"");
00408   TRACE("search literals", "updateLitScores(size=", d_litsByScores.size(),
00409   ") => }");
00410 }
00411 
00412 void SearchEngineFast::updateLitCounts(const Clause& c)
00413 {
00414   TRACE("search literals", "updateLitCounts(", CompactClause(c), ") {");
00415   for(unsigned i=0; i<c.size(); ++i) {
00416     // Assign by value to modify the attributes
00417     Literal lit = c[i];
00418     DebugAssert(lit.getExpr().isAbsLiteral(),"Expected literal");
00419     // Only add the literal if it wasn't added before.  The literal
00420     // counts are taken care of in Clause constructors/destructors.
00421 //     if(!lit.added() || lit.count() != lit.countPrev())
00422     d_litSortCount--;
00423     
00424     if(!lit.added()) {
00425       TRACE("search literals", "adding literal ", lit, " to d_litsByScores");
00426       d_litsByScores.push_back(lit);
00427       lit.added()=true;
00428     }
00429   }
00430   if(d_litSortCount < 0) {
00431     ::stable_sort(d_litsByScores.begin(), d_litsByScores.end(), compareLits);
00432     d_litSortCount=d_litsByScores.size();
00433   }
00434   TRACE("search splitters","updateLitCounts => ", lits2str(d_litsByScores),"");
00435   TRACE_MSG("search literals", "updateLitCounts => }");
00436 }
00437 
00438 Expr SearchEngineFast::findSplitter()
00439 {
00440   TRACE_MSG("splitters", "SearchEngineFast::findSplitter() {");
00441   Expr splitter; // Null by default
00442   unsigned i;
00443 
00444   // if we have a conflict clause, pick the one inside with the
00445   // best ac(z) score (from the most recent conflict clause)
00446   //  if (d_berkminFlag && !d_conflictClauses.empty())
00447   if (d_berkminFlag && !d_conflictClauses->empty())
00448   {
00449     unsigned sCount = 0;
00450     std::deque<ClauseOwner>::reverse_iterator foundUnsat = d_conflictClauses->rend();
00451     for (std::deque<ClauseOwner>::reverse_iterator i = d_conflictClauses->rbegin();
00452          i != d_conflictClauses->rend();
00453          ++i) {
00454       ++sCount;
00455       if (!((Clause)*i).sat(true)) {
00456         foundUnsat = i;
00457         break;
00458       }
00459     }
00460     if (foundUnsat != d_conflictClauses->rend()) {
00461       Clause &topClause = *foundUnsat;
00462       int numLits = topClause.size();
00463       int bestScore = 0;
00464       int bestLit = -1;
00465       unsigned numChoices = 0;
00466       for (int i = 0; i < numLits; ++i) {
00467   const Literal& lit = topClause[i];
00468         if (lit.getValue() != 0) continue;
00469         if (bestLit == -1) bestLit = i;
00470         ++numChoices;
00471         int s = lit.score();
00472         if (s > bestScore) {
00473           bestLit = i;
00474           bestScore = s;
00475         }
00476       }
00477       if (bestLit != -1) {
00478   splitter = topClause[bestLit].getExpr();
00479         IF_DEBUG(debugger.counter("BerkMin heuristic")++;)
00480         TRACE("splitters", "SearchEngineFast::findSplitter()[berkmin] => ",
00481         splitter, " }"); 
00482         return splitter;
00483       }
00484     }
00485   } 
00486 
00487   /*
00488   // Search for DP-specific splitters
00489   for(CDMapOrdered<Splitter,bool>::iterator i=d_dpSplitters.begin(),
00490   iend=d_dpSplitters.end(); i!=iend; ++i) {
00491     Expr e((*i).first.expr);
00492     if(e.isBoolConst() || d_core->find(e).getRHS().isBoolConst())
00493       continue;
00494     return e;
00495   }
00496   */
00497 
00498   for (int i = d_nonLiterals.size()-1; i >= 0; --i) {
00499     const Expr& e = d_nonLiterals[i].get().getExpr();
00500     if (e.isTrue()) continue;
00501     //    if (d_nonLiteralSimplified[thm.getExpr()]) continue;
00502     DebugAssert(!e.isBoolConst(), "Expected non-bool const");
00503     DebugAssert(d_core->simplifyExpr(e) == e,
00504         "Expected non-literal to be simplified:\n e = "
00505     +e.toString()+"\n simplify(e) = "
00506     +d_core->simplifyExpr(e).toString());
00507     splitter = d_decisionEngine->findSplitter(e);
00508     //DebugAssert(!splitter.isNull(),
00509     //            "findSplitter: can't find splitter in non-literal: "
00510     //            + e.toString());
00511     if (splitter.isNull()) continue;
00512     IF_DEBUG(debugger.counter("splitters from non-literals")++;)          
00513     TRACE("splitters", "SearchEngineFast::findSplitter()[non-lit] => ",
00514     splitter, " }"); 
00515     return splitter;
00516   }
00517 
00518   // Update the scores: we are about to choose a splitter based on them
00519   if (d_splitterCount <= 0) {
00520     updateLitScores(false);
00521 //     d_splitterCount = d_litsByScores.size();
00522 //     if(d_splitterCount > 100)
00523       d_splitterCount = 0x10;
00524   } else
00525     d_splitterCount--;
00526   // pick splitter based on score
00527   for (i=d_litsMaxScorePos; i<d_litsByScores.size(); ++i) {
00528     const Literal& splitterLit = d_litsByScores[i];
00529     TRACE("search splitters", "d_litsByScores["+int2string(i)+"] = ",
00530     splitterLit,"");
00531     //if (d_core->simplifyExpr(splitter).isBoolConst()) continue;
00532     if(splitterLit.getValue() != 0) continue;
00533     splitter = splitterLit.getExpr();
00534     // Skip auxiliary CNF vars
00535     if(!isGoodSplitter(splitter)) continue;
00536     d_litsMaxScorePos = i+1;
00537     IF_DEBUG(debugger.counter("splitters from literals")++;)
00538     TRACE("splitters", "d_litsMaxScorePos: ", d_litsMaxScorePos, "");
00539     TRACE("splitters", "SearchEngineFast::findSplitter()[lit] => ",
00540     splitter, " }"); 
00541     return splitter;
00542   }
00543   TRACE_MSG("splitters",
00544       "SearchEngineFast::findSplitter()[not found] => Null }");
00545   return Expr();
00546 }
00547 
00548 
00549 void SearchEngineFast::recordFact(const Theorem& thm)
00550 {
00551   Literal l(newLiteral(thm.getExpr()));
00552   if(l.getValue() == 0) {
00553     l.setValue(thm, thm.getScope());
00554     IF_DEBUG(debugger.counter("recordFact adds unreported lit")++;)
00555     d_unreportedLits.insert(l.getExpr(),thm,thm.getScope());
00556   } else if (l.getValue() == 1 && l.getScope() > thm.getScope()) {
00557     // Cannot do this, it will trigger DebugAssert
00558     // l.setValue(thm,thm.getScope());
00559     IF_DEBUG(debugger.counter("recordFact adds unreported lit")++;)
00560     d_unreportedLits.insert(l.getExpr(),thm,thm.getScope());
00561   } else if(l.getValue() < 0) { // Contradiction, bcp will die anyway
00562     if(l.isNegative())
00563       setInconsistent(d_commonRules->contradictionRule(l.deriveTheorem(), thm));
00564     else
00565       setInconsistent(d_commonRules->contradictionRule(thm, l.deriveTheorem()));
00566   }
00567   //else if (thm.getScope() < scopeLevel())
00568   //  d_unreportedLits.insert(l.getExpr(),l,thm.getScope());
00569   
00570 }
00571 
00572 #ifdef _CVC3_DEBUG_MODE
00573 void SearchEngineFast::fullCheck()
00574 {
00575   for (unsigned i = 0;
00576        i < d_clauses.size();
00577        ++i) {
00578     if (!((Clause)d_clauses[i]).sat()) {
00579       bool sat = false;
00580       const Clause &theClause = d_clauses[i];
00581       unsigned numLits = theClause.size();
00582       unsigned numChoices = 0;
00583       for (unsigned j = 0; !sat && j < numLits; ++j) {
00584         if (theClause[j].getValue() == 0)
00585           ++numChoices;
00586         else if (theClause[j].getValue() == 1)
00587           sat = true;
00588       }
00589       if (sat) continue;
00590       if (numChoices <= 1 || !theClause.wpCheck()) {
00591         CVC3::debugger.getOS() << CompactClause(theClause) << endl;
00592         CVC3::debugger.getOS() << theClause.toString() << endl;
00593       }
00594       DebugAssert(numChoices > 1, "BCP postcondition violated: unsat or unit clause(s)");
00595       DebugAssert(theClause.wpCheck(), "Watchpointers broken");
00596     }
00597   }
00598 
00599   if (!d_conflictClauses->empty())
00600   {
00601     for (std::deque<ClauseOwner>::reverse_iterator i = d_conflictClauses->rbegin();
00602          i != d_conflictClauses->rend();
00603          ++i) {
00604       if (!((Clause)*i).sat()) {
00605         bool sat = false;
00606         Clause &theClause = *i;
00607         unsigned numLits = theClause.size();
00608         unsigned numChoices = 0;
00609         for (unsigned j = 0; !sat && j < numLits; ++j) {
00610            if (theClause[j].getValue() == 0)
00611             ++numChoices; 
00612            else if (theClause[j].getValue() == 1)
00613              sat = true;
00614         }
00615         if (sat) continue;
00616         if (numChoices <= 1 || !theClause.wpCheck()) {
00617           CVC3::debugger.getOS() << CompactClause(theClause) << endl;
00618           CVC3::debugger.getOS() << theClause.toString() << endl;
00619         }
00620         
00621         DebugAssert(numChoices > 1, "BCP postcondition violated: unsat or unit conflict clause(s)");
00622         DebugAssert(theClause.wpCheck(), "Watchpointers broken");
00623       
00624       }
00625     }
00626   } 
00627 }
00628 #endif
00629 
00630 
00631 void SearchEngineFast::clearLiterals() {
00632   TRACE_MSG("search literals", "clearLiterals()");
00633   d_literals.clear();
00634 }
00635 
00636 
00637 bool SearchEngineFast::bcp()
00638 {
00639   TRACE("search bcp", "bcp@"+int2string(scopeLevel())+"(#lits=",
00640   d_literals.size(), ") {");
00641   IF_DEBUG(TRACE_MSG("search bcp", "literals=[\n");
00642      for(size_t i=0,iend=d_literals.size(); i<iend; i++)
00643      TRACE("search bcp", "          ", d_literals[i], ",");
00644      TRACE_MSG("search bcp", "]");)
00645   DebugAssert(d_factQueue.empty(), "bcp(): start");
00646   bool newInfo = true;
00647   /*
00648   CDMap<Expr,Theorem>::iterator i = d_unreportedLits.begin(),
00649     iend = d_unreportedLits.end();
00650   for (; i != iend; ++i) {
00651     if (d_unreportedLitsHandled[(*i).first])
00652       continue;
00653     Theorem thm((*i).second);
00654     Literal l(newLiteral(thm.getExpr()));
00655     DebugAssert(l.getValue() != -1, "Bad unreported literal: "+l.toString());
00656     if(l.getValue() == 0) l.setValue(thm, scopeLevel());
00657     IF_DEBUG(debugger.counter("re-assert unreported lits")++;)
00658     DebugAssert(l.getExpr().isAbsLiteral(),
00659                 "bcp(): pushing non-literal to d_literals:\n "
00660                 +l.getExpr().toString());
00661     // The literal may be set to 1, but not on the list; push it here
00662     // explicitly
00663     d_literals.push_back(l);
00664     //recordFact((*i).second.getTheorem());
00665     enqueueFact(thm);
00666     d_unreportedLitsHandled[(*i).first] = true;
00667   }
00668   */
00669   while (newInfo) {
00670     IF_DEBUG(debugger.counter("BCP: while(newInfo)")++;)
00671     TRACE_MSG("search bcp", "while(newInfo) {");
00672     newInfo = false;
00673     while(!d_core->inconsistent() && d_literals.size() > 0) {
00674      for(unsigned i=0; !d_core->inconsistent() && i<d_literals.size(); ++i) {
00675       Literal l = d_literals[i];
00676       TRACE("search props", "Propagating literal: [", l.toString(), "]");
00677       DebugAssert(l.getValue() == 1, "Bad literal is d_literals: "
00678                   +l.toString());
00679       d_litsAlive.push_back(l);
00680       // Use the watch pointers to find more literals to assert.  Repeat
00681       // until conflict.  Once conflict found, call unsatClause() to
00682       // assert the contradiction.
00683       std::vector<std::pair<Clause, int> >& wps = wp(l);
00684       TRACE("search props", "Appears in ", wps.size(), " clauses.");
00685       for(unsigned j=0; j<wps.size(); ++j) {
00686         const Clause& c = wps[j].first;
00687         int k = wps[j].second;
00688         DebugAssert(c.watched(k).getExpr() == (!l).getExpr(),
00689                     "Bad watched literal:\n l = "+l.toString()
00690                     +"\n c[k] = "+c.watched(k).toString());
00691         if(c.deleted()) { // Remove the clause from the list
00692           if(wps.size() > 1) {
00693             wps[j] = wps.back();
00694             --j;
00695           }
00696           wps.pop_back();
00697         } else if(true || !c.sat()) {
00698           // Call BCP to update the watch pointer
00699           bool wpUpdated;
00700           bool conflict = !propagate(c, k, wpUpdated);
00701           // Delete the old watch pointer from the list
00702           if(wpUpdated) {
00703             if(wps.size() > 1) {
00704               wps[j] = wps.back();
00705               --j;
00706             }
00707             wps.pop_back();
00708           }
00709           if (conflict) {
00710       clearFacts();
00711       DebugAssert(d_factQueue.empty(), "bcp(): conflict");
00712       TRACE_MSG("search bcp", "bcp[conflict] => false }}");
00713             return false;
00714     }
00715         }
00716       }
00717 
00718       vector<Circuit*>& cps = d_circuitsByExpr[l.getExpr()];
00719       for (vector<Circuit*>::iterator it = cps.begin(), end = cps.end();
00720            it < end; it++)
00721       {
00722         if (!(*it)->propagate(this)) {
00723     clearFacts();
00724     DebugAssert(d_factQueue.empty(), "bcp(): conflict-2");
00725     TRACE_MSG("search bcp", "bcp[circuit propagate] => false }}");
00726           return false;
00727   }
00728       }
00729      }
00730      // Finished with BCP* (without DPs).
00731      clearLiterals();
00732      // Now, propagate the facts to DPs and repeat ((BCP*); DP) step
00733      if(!d_core->inconsistent()) commitFacts();
00734     }
00735     if (d_core->inconsistent()) {
00736       d_conflictTheorem = d_core->inconsistentThm();
00737       clearFacts();
00738       TRACE_MSG("search bcp", "bcp[DP conflict] => false }}");
00739       return false;
00740     }
00741     else
00742       TRACE("search basic", "Processed ", d_literals.size(), " propagations");
00743     IF_DEBUG(fullCheck();)
00744     clearLiterals();
00745 
00746     bool dfs_heuristic = (d_core->getFlags()["de"].getString() == "dfs");
00747     TRACE("search dfs", "DFS is ", (dfs_heuristic? "on" : "off"),
00748     " (de = "+d_core->getFlags()["de"].getString()+") {");
00749     // When DFS heuristic is used, simplify the nonliterals only until
00750     // there is a completely simplified one on top of the stack, or
00751     // all of the non-literals are gone.  Start from the end of the
00752     // list (top of the stack), since that's where the splitter is
00753     // most likely chosen.  This way we are likely to hit something
00754     // that simplifies very soon.
00755 
00756     size_t origSize = d_nonLiterals.size();
00757     bool done(false);
00758     for(int i=origSize-1; !done && !d_core->inconsistent() && i>=0; --i) {
00759       const Theorem& thm = d_nonLiterals[i].get();
00760       const Expr& e = thm.getExpr();
00761       TRACE("search dfs", "Simplifying non-literal", e, "");
00762       if (e.isTrue()) {
00763         //      if (d_nonLiteralSimplified[thm.getExpr()]) {
00764   IF_DEBUG(debugger.counter("BCP: simplified non-literals: skipped [stale]")++;)
00765   TRACE_MSG("search bcp", "}[continue]// end of while(newInfo)");
00766   continue;
00767       }
00768       IF_DEBUG(debugger.counter("BCP: simplified non-literals")++;)
00769       Theorem simpThm = simplify(thm);
00770       Expr simp = simpThm.getExpr();
00771       if(simp != e) {
00772   IF_DEBUG(debugger.counter("BCP: simplified non-literals: changed")++;)
00773         newInfo = true;
00774         //        d_nonLiteralSimplified[thm.getExpr()] = true;
00775         if (!simp.isFalse()) {
00776           while (simp.isExists()) {
00777             simpThm = d_commonRules->skolemize(simpThm);
00778             simp = simpThm.getExpr();
00779           }
00780           if (simp.isAbsLiteral()) {
00781             enqueueFact(simpThm);
00782             commitFacts();
00783           }
00784           d_nonLiterals[i] = simpThm;
00785     if(dfs_heuristic) {
00786       // Something has changed, time to stop this loop.  If we
00787       // also get a new non-literal on top of the stack, and no
00788       // new literals, then stop the entire BCP (since that
00789       // non-literal is guaranteed to be fully simplified).
00790       done = true;
00791       if(d_nonLiterals.size() > origSize && d_literals.empty())
00792         newInfo = false;
00793     }
00794         } else
00795           setInconsistent(simpThm);
00796       } else if (dfs_heuristic) done = true;
00797     }
00798     TRACE("search dfs", "End of non-literal simplification: newInfo = ",
00799     (newInfo? "true" : "false"), " }}");
00800     if (d_core->inconsistent()) {
00801       d_conflictTheorem = d_core->inconsistentThm();
00802       DebugAssert(d_factQueue.empty(), "bcp(): inconsistent (nonLits)");
00803       TRACE_MSG("search bcp", "bcp[nonCNF conflict] => false }}");
00804       return false;
00805     }
00806     TRACE_MSG("search bcp", "}// end of while(newInfo)");
00807   }
00808   IF_DEBUG(fullCheck();)
00809   DebugAssert(d_factQueue.empty(), "bcp(): end");
00810   TRACE_MSG("search bcp", "bcp => true }");
00811   return true;
00812 }
00813 
00814 
00815 // True if successfully propagated.  False if conflict.
00816 bool SearchEngineFast::propagate(const Clause &c, int idx, bool& wpUpdated)
00817 {
00818   TRACE("search propagate", "propagate(", CompactClause(c),
00819   ", idx = "+int2string(idx)+") {");
00820   DebugAssert(idx==0 || idx==1, "propagate(): bad index = "+int2string(idx));
00821   // The current watched literal must be set to FALSE, unless the
00822   // clause is of size 1
00823   DebugAssert((c.size() == 1) ||  c.watched(idx).getValue() < 0,
00824         "propagate(): this literal must be FALSE: c.watched("
00825         +int2string(idx)+")\n c = "+c.toString());
00826   wpUpdated = false;
00827   int lit = c.wp(idx), otherLit = c.wp(1-idx);
00828   int dir = c.dir(idx);
00829   int size = c.size();
00830   while(true) {
00831     TRACE_MSG("search propagate", "propagate: lit="+int2string(lit)
00832         +", otherLit="+int2string(otherLit)+", dir="+int2string(dir));
00833     lit += dir;
00834     if(lit < 0 || lit >= size) { // hit the edge
00835       if(dir == c.dir(idx)) {
00836   // Finished first half of the clause, do the other half
00837   lit = c.wp(idx);
00838   dir = -dir;
00839   continue;
00840       }
00841       // All literals are false, except for the other watched literal.
00842       // Check its value.
00843       Literal l(c[otherLit]);
00844       if(l.getValue() < 0) { // a conflict
00845   //Literal ff(newLiteral(d_vcl->getEM()->falseExpr()));
00846   //ff.setValue(1, c, -1);
00847         //d_lastBCPConflict = ff;
00848         vector<Theorem> thms;
00849         for (unsigned i = 0; i < c.size(); ++i)
00850           thms.push_back(c[i].getTheorem());
00851         d_conflictTheorem = d_rules->conflictRule(thms,c.getTheorem());
00852   TRACE("search propagate", "propagate[", CompactClause(c),
00853         "] => false }");
00854         return false;
00855       }
00856       else if(l.getValue() == 0) {
00857         DebugAssert(c.size() > 1 && l.getExpr().isAbsLiteral(), "BCP: Expr should be literal");
00858         d_unitPropCount++;
00859         c.markSat();
00860         // Let's prove the new literal instead of playing assumption games
00861         unitPropagation(c,otherLit);
00862         //l.setValue(1, c, otherLit);
00863         //d_core->addFact(createAssumption(l));
00864   TRACE("search propagate", "propagate[", CompactClause(c),
00865         "] => true }");
00866         return true;
00867       }
00868       else {
00869         c.markSat();
00870   TRACE("search propagate", "propagate[", CompactClause(c),
00871         "] => true }");
00872         return true;
00873       }
00874     }
00875     // If it's the other watched literal, skip it
00876     if(lit == otherLit) continue;
00877 
00878     Literal l(c[lit]);
00879     int val(l.getValue());
00880     // if it is false, keep looking
00881     if(val < 0) continue;
00882     // OPTIMIZATION: if lit is TRUE, mark the clause SAT and give up.
00883     // FIXME: this is different from Chaff.  Make sure it doesn't harm
00884     // the performance.
00885      if(val > 0) {
00886        c.markSat();
00887 //       return true;
00888      }
00889 
00890     // Now the value of 'lit' is unknown.  Set the watch pointer to
00891     // this literal, if it is indeed a literal (it may be any formula
00892     // in a pseudo-clause), and update the direction.
00893     c.wp(idx, lit);
00894     c.dir(idx, dir);
00895     DebugAssert(c.watched(idx).getValue() >= 0,
00896     "Bad watched literals in clause:\n"
00897     +CompactClause(c).toString());
00898     // Get the expression of the literal's inverse
00899     Literal inv(!c[lit]);
00900     // If it is indeed a literal, update the watch pointers
00901     DebugAssert(inv.getExpr().isAbsLiteral(), "Expr should be literal: inv = "
00902     +inv.getExpr().toString());
00903     // Add the new watched literal to the watch pointer list
00904     pair<Clause, int> p(c, idx);
00905     wp(inv).push_back(p);
00906 
00907     // Signal to remove the old watch pointer
00908     wpUpdated = true;
00909     TRACE("search propagate", "propagate[", CompactClause(c),
00910     "] => true }");
00911     return true;
00912   }
00913 }
00914 
00915 void SearchEngineFast::unitPropagation(const Clause &c, unsigned idx)
00916 {  
00917   vector<Theorem> thms;
00918   for (unsigned i = 0; i < c.size(); ++i)
00919     if (i != idx) {
00920       thms.push_back(c[i].getTheorem());
00921       DebugAssert(!thms.back().isNull(),
00922       "unitPropagation(idx = "+int2string(idx)+", i = "
00923       +int2string(i)+",\n"+c.toString()+")");
00924     }
00925   Theorem thm(d_rules->unitProp(thms,c.getTheorem(),idx));
00926   enqueueFact(thm); // d_core->addFact(thm);
00927   // recordFact(thm);
00928 
00929   DebugAssert(thm.isAbsLiteral(),
00930         "unitPropagation(): pushing non-literal to d_literals:\n "
00931         +thm.getExpr().toString());
00932   Literal l(newLiteral(thm.getExpr()));
00933   DebugAssert(l.getValue() == 1, "unitPropagation: bad literal: "
00934         +l.toString());
00935   d_literals.push_back(l);
00936 }
00937 
00938 
00939 bool SearchEngineFast::fixConflict()
00940 {
00941   TRACE_MSG("search basic", "FixConflict");
00942   Theorem res, conf;
00943   d_conflictCount++;
00944   TRACE("conflicts", "found conflict # ", d_conflictCount, "");
00945   IF_DEBUG(if(debugger.trace("impl graph verbose")) {
00946     d_conflictTheorem.printDebug();
00947   })
00948 
00949   if (scopeLevel() == d_bottomScope)
00950     return false;
00951   else if(d_conflictTheorem.getScope() <= d_bottomScope) {
00952     d_decisionEngine->popTo(d_bottomScope);
00953     d_litsMaxScorePos = 0; // from decision engine
00954     clearLiterals();
00955     return false;
00956   }
00957 
00958   traceConflict(d_conflictTheorem);
00959   
00960   if (d_lastConflictScope <= d_bottomScope)
00961     return false;
00962 
00963   // If we have unit conflict clauses, then we have to bounce back to
00964   // the original scope and assert them.
00965   if(d_unitConflictClauses.size() > 0) {
00966     TRACE_MSG("search basic", "Found unit conflict clause");
00967     d_decisionEngine->popTo(d_bottomScope);
00968     d_litsMaxScorePos = 0; // from decision engine
00969     clearLiterals();
00970     for (vector<Clause>::reverse_iterator i = d_unitConflictClauses.rbegin();
00971          i != d_unitConflictClauses.rend();
00972          ++i) {
00973       //IF_DEBUG(checkAssumpDebug(i->getTheorem(), d_assumptions);)
00974       // The theorem of *i is, most likely, (OR lit); rewrite it to just `lit'
00975       Theorem thm = i->getTheorem();
00976       if(thm.getExpr().isOr())
00977   thm = d_commonRules->iffMP(thm, d_commonRules->rewriteOr(thm.getExpr()));
00978       enqueueFact(thm);
00979       commitFacts(); // Make sure facts propagate to DPs
00980     }
00981     d_unitConflictClauses.clear();
00982     return true; // Let bcp take care of the rest.
00983   }
00984 
00985   // Otherwise, we need to make our failure driven assertion.
00986   DebugAssert(!d_lastConflictClause.isNull(), "");
00987 
00988   // We need to calculate the backtracking level.  We do this by
00989   // examining the decision levels of all the literals involved in the
00990   // last conflict clause.
00991 
00992   Clause &c = d_lastConflictClause;
00993   Literal unit_lit;
00994   unsigned idx=0;
00995   unsigned current_dl = d_lastConflictScope;
00996   unsigned back_dl = d_bottomScope;
00997   for (unsigned i = 0; i < c.size(); ++i) {
00998     unsigned dl = c[i].getVar().getScope();
00999     if (dl < current_dl) {
01000       if (dl > back_dl)
01001         back_dl = dl;
01002     }
01003     else {
01004       DebugAssert(unit_lit.getExpr().isNull(),
01005       "Only one lit from the current decision level is allowed.\n"
01006       "current_dl="
01007       +int2string(current_dl)+", scopeLevel="
01008       +int2string(scopeLevel())
01009       +"\n l1 = "
01010       +unit_lit.toString()
01011       +"\n l2 = "+c[i].toString()
01012       +"\nConflict clause: "+c.toString());
01013       unit_lit = c[i];
01014       idx = i;
01015     }
01016   }
01017 
01018 
01019   // Now we have the backtracking decision level.
01020   DebugAssert(!unit_lit.getExpr().isNull(),"Need to have an FDA in "
01021         "conflict clause: "+c.toString());
01022   d_decisionEngine->popTo(back_dl);
01023   d_litsMaxScorePos = 0; // from decision engine
01024   clearLiterals();
01025   unitPropagation(c,idx);
01026   commitFacts(); // Make sure facts propagate to DPs
01027   return true;
01028 }
01029 
01030 
01031 void SearchEngineFast::enqueueFact(const Theorem& thm) {
01032   //  d_core->addFact(thm);
01033   TRACE("search props", "SearchEngineFast::enqueueFact(",
01034   thm.getExpr(), ") {");
01035   if(thm.isAbsLiteral()) {
01036     addLiteralFact(thm);
01037   }
01038   d_factQueue.push_back(thm);
01039   TRACE_MSG("search props", "SearchEngineFast::enqueueFact => }");
01040 }
01041 
01042 
01043 void SearchEngineFast::setInconsistent(const Theorem& thm) {
01044   TRACE_MSG("search props", "SearchEngineFast::setInconsistent()");
01045   d_factQueue.clear();
01046   IF_DEBUG(debugger.counter("conflicts from SAT solver")++;)
01047   d_core->setInconsistent(thm);
01048 }
01049 
01050 void SearchEngineFast::commitFacts() {
01051   for(vector<Theorem>::iterator i=d_factQueue.begin(), iend=d_factQueue.end();
01052       i!=iend; ++i) {
01053     TRACE("search props", "commitFacts(", i->getExpr(), ")");
01054     if(d_useEnqueueFact)
01055       d_core->enqueueFact(*i);
01056     else
01057       d_core->addFact(*i);
01058   }
01059   d_factQueue.clear();
01060 }
01061 
01062 
01063 void SearchEngineFast::clearFacts() {
01064   TRACE_MSG("search props", "clearFacts()");
01065   d_factQueue.clear();
01066 }
01067 
01068 
01069 void SearchEngineFast::addNewClause(Clause &c)
01070 {
01071   DebugAssert(c.size() > 1, "New clauses should have size > 1");
01072   d_clauses.push_back(c);
01073   updateLitCounts(c);
01074   // Set up the watch pointers to this clause: find two unassigned
01075   // literals (otherwise we shouldn't even receive it as a clause)
01076   size_t i=0, iend=c.size();
01077   for(; i<iend && c[i].getValue() != 0; ++i);
01078   DebugAssert(i<iend, "SearchEngineFast::addNewClause:\n"
01079         "no unassigned literals in the clause:\nc = "
01080         +CompactClause(c).toString());
01081   c.wp(0,i); ++i;
01082   for(; i<iend && c[i].getValue() != 0; ++i);
01083   DebugAssert(i<iend, "SearchEngineFast::addNewClause:\n"
01084         "Only one unassigned literal in the clause:\nc = "
01085         +CompactClause(c).toString());
01086   c.wp(1,i);
01087   // Add the watched pointers to the appropriate lists
01088   for(int i=0; i<=1; i++) {
01089     Literal l(!c.watched(i));
01090     // Add the pointer to l's list
01091     pair<Clause, int> p(c, i);
01092     wp(l).push_back(p);
01093   }
01094 }
01095 
01096 inline bool TheoremEq(const Theorem& t1, const Theorem& t2) {
01097   DebugAssert(!t1.isNull() && !t2.isNull(),
01098         "analyzeUIPs() Null Theorem found");
01099    return t1.getExpr() == t2.getExpr();
01100 }
01101 
01102 
01103 //! Auxiliary function used in analyzeUIPs()
01104 /*! It processes a node and populates the relevant sets used in the
01105  * algorithm.
01106  * \sa analyzeUIPs() for more detail). 
01107  */
01108 static void processNode(const Theorem& thm, 
01109       vector<Theorem>& lits,
01110       vector<Theorem>& gamma,
01111       vector<Theorem>& fringe,
01112       int& pending) {
01113   // Decrease the fan-out count
01114   int fanOutCount(thm.getCachedValue() - 1);
01115   thm.setCachedValue(fanOutCount);
01116   bool wasFlagged(thm.isFlagged());
01117   thm.setFlag();
01118   DebugAssert(fanOutCount >= 0, 
01119         "analyzeUIPs(): node visited too many times: "
01120         +thm.toString());
01121   if(fanOutCount == 0) {
01122     if(thm.getExpandFlag()) {
01123       if(wasFlagged) {
01124   TRACE("impl graph", "pending.erase(", thm.getExpr(), ")");
01125   DebugAssert(pending > 0, 
01126         "analyzeUIPs(): pending set shouldn't be empty here");
01127   pending--;
01128       }
01129       TRACE("impl graph", "fringe.insert(", thm.getExpr(), ")");
01130       fringe.push_back(thm);
01131     } else if(thm.getLitFlag()) {
01132       DebugAssert(thm.isAbsLiteral(), "analyzeUIPs(): bad flag on "
01133       +thm.toString());
01134       if(wasFlagged) {
01135   TRACE("impl graph", "pending.erase(", thm.getExpr(), ")");
01136   DebugAssert(pending > 0, 
01137         "analyzeUIPs(): pending set shouldn't be empty here");
01138   pending--;
01139       }
01140       TRACE("impl graph", "lits.insert(", thm.getExpr(), ")");
01141       lits.push_back(thm);
01142     } else {
01143       if(!wasFlagged) {
01144   TRACE("impl graph", "gamma.insert(", thm.getExpr(), ")");
01145   gamma.push_back(thm);
01146       } else {
01147   TRACE("impl graph", "already in gamma: ", thm.getExpr(), "");
01148       }
01149     }
01150   } else { // Fan-out count is non-zero
01151     if(thm.getExpandFlag()) {
01152       // Too early to expand; stash in pending
01153       if(!wasFlagged) {
01154   pending++;
01155   TRACE("impl graph", "pending.insert(", thm.getExpr(), ")");
01156       } else {
01157   TRACE("impl graph", "already in pending: ", thm.getExpr(), "");
01158       }
01159     } else if(thm.getLitFlag()) {
01160       // It's a literal which goes into pending
01161       if(!wasFlagged) {
01162   pending++;
01163   TRACE("impl graph", "pending.insert(", thm.getExpr(), ")");
01164       } else {
01165   TRACE("impl graph", "already in pending: ", thm.getExpr(), "");
01166       }
01167     } else {
01168       if(!wasFlagged) {
01169   TRACE("impl graph", "gamma.insert(", thm.getExpr(), ")");
01170   gamma.push_back(thm);
01171       } else {
01172   TRACE("impl graph", "already in gamma: ", thm.getExpr(), "");
01173       }
01174     }
01175   }
01176   // FIXME: uniquify theorems in lits, gamma, and fringe by
01177   // expression; the smallest scope theorem should supersede all the
01178   // duplicates.  Question: can we do it safely, without breaking the
01179   // UIP algorithm?
01180 }
01181 
01182 /*! 
01183  <strong>Finding UIPs (Unique Implication Pointers)</strong>
01184 
01185  This is basically the same as finding hammocks of the subset of the
01186  implication graph composed of only the nodes from the current scope.
01187  A hammock is a portion of the graph which has a single source and/or
01188  sink such that removing that single node makes the graph
01189  disconnected.
01190 
01191  Conceptually, the algorithm maintains four sets of nodes: literals
01192  (named <em>lits</em>), gamma, fringe, and pending.  Literals are
01193  nodes whose expressions will become literals in the conflict clause
01194  of the current hammock, and the nodes in gamma are assumptions from
01195  which such conflict clause theorem is derived.  Nodes in fringe are
01196  intermediate nodes which are ready to be "expanded" (see the
01197  algorithm description below).  The pending nodes are those which are
01198  not yet ready to be processed (they later become literal or fringe
01199  nodes).
01200 
01201  These sets are maintained as vectors, and are updated in such a way
01202  that the nodes in the vectors never repeat.  The exception is the
01203  pending set, for which only a size counter is maintained.  A node
01204  belongs to the pending set if it has been visited (isFlagged()
01205  method), and its fan-out count is non-zero (stored in the cache,
01206  getCachedValue()).  In other words, pending nodes are those that have
01207  been visited, but not sufficient number of times.
01208 
01209  Also, fringe is maintained as a pair of vectors.  One vector is
01210  always the current fringe, and the other one is built when the
01211  current is processed.  When processing of the current fringe is
01212  finished, it is cleared, and the other vector becomes the current
01213  fringe (that is, they swap roles).
01214 
01215  A node is expanded if it is marked for expansion (getExpandFlag()).
01216  If its fan-out count is not yet zero, it is added to the set of
01217  pending nodes.
01218 
01219  If a node has a literal flag (getLitFlag()), it goes into literals
01220  when its fan-out count reaches zero.  Since this will be the last
01221  time the node is visited, it is added to the vector only once.
01222 
01223  A node neither marked for expansion nor with the literal flag goes
01224  into the gamma set.  It is added the first time the node is visited
01225  (isFlagged() returns false), and therefore, is added to the vector
01226  only once.  This is an important distinction from the other sets,
01227  since a gamma-node may be used by several conflict clauses.
01228 
01229  Clearing the gamma set after each UIP requires both clearing the
01230  vector and resetting all flags (clearAllFlags()).
01231 
01232  <strong>The algorithm</strong>
01233 
01234 <ol>
01235 
01236 <li> Initially, the fringe contains exactly the predecessors of
01237     falseThm from the current scope which are ready to be expanded
01238     (fan-out count is zero).  All the other predecessors of falseThm
01239     go to the appropriate sets of literals, gamma, and pending.
01240 
01241 <li> If fringe.size() <= 1 and the set of pending nodes is empty, then
01242     the element in the fringe (if it's non-empty) is a UIP.  Generate
01243     a conflict clause from the UIP and the literals (using gamma as
01244     the set of assumptions), empty the sets, and continue with the
01245     next step.  Note, that the UIP remains in the fringe, and will be
01246     expanded in the next step.
01247 
01248     The important exception: if the only element in the fringe is
01249     marked for expansion, then this is a false UIP (the SAT solver
01250     doesn't know about this node), and it should not appear in the
01251     conflict clause.  In this case, simply proceed to step 3 as if
01252     nothing happened.
01253 
01254 <li> If fringe.size()==0, stop (the set of pending nodes must also be
01255     empty at this point).  Otherwise, for *every* node in the fringe,
01256     decrement the fan-out for each of its predecessors, and empty the
01257     fringe.  Take the predecessors from the current scope, and add
01258     those to the fringe for which fan-out count is zero, and remove
01259     them from the set of pending nodes.  Add the other predecessors
01260     from the current scope to the set of pending nodes.  Add the
01261     remaining predecessors (not from the current scope) to the
01262     literals or gamma, as appropriate.  Continue with step 2.
01263 
01264 </ol>
01265 */
01266 void SearchEngineFast::analyzeUIPs(const Theorem &falseThm, int conflictScope)
01267 {
01268   TRACE("impl graph", "analyzeUIPs(scope = ", conflictScope, ") {");
01269   vector<Theorem> fringe[2]; // 2-element array of vectors (new & curr. fringe)
01270   unsigned curr(0), next(1);
01271 
01272   int pending(0);
01273   vector<Theorem> lits;
01274   vector<Theorem> gamma;
01275   
01276   Theorem start = falseThm;
01277   d_lastConflictClause = Clause();
01278   d_lastConflictScope = conflictScope;
01279   start.clearAllFlags();
01280 
01281   TRACE("search full", "Analysing UIPs at level: ", conflictScope, "");
01282 
01283   // Initialize all the sets
01284   const Assumptions& a=start.getAssumptionsRef();
01285   for(Assumptions::iterator i=a.begin(), iend=a.end(); i!=iend; ++i) {
01286     processNode(*i, lits, gamma, fringe[curr], pending);
01287   }
01288 
01289   while (true) {
01290     TRACE_MSG("impl graph", "analyzeUIPs(): fringe size = "
01291         +int2string(fringe[curr].size())
01292         +", pending size = "+int2string(pending));
01293     // Wrap up a conflict clause if:
01294     // (1) There are no pending nodes
01295     // (2) The fringe has at most one element
01296     // (3) If fringe is not empty, its node should not be flagged for expansion
01297     if(fringe[curr].size() <= 1 && pending == 0
01298        && (fringe[curr].size() == 0
01299      || !fringe[curr].back().getExpandFlag())) {
01300       // Found UIP or end of graph.  Generate conflict clause.
01301       if(fringe[curr].size() > 0)
01302   lits.push_back(fringe[curr].back());
01303       IF_DEBUG(if(debugger.trace("impl graph")) {
01304   ostream& os = debugger.getOS();
01305   os << "Creating conflict clause:"
01306      << "\n  start: " << start.getExpr()
01307      << "\n  Lits: [\n";
01308   for(size_t i=0; i<lits.size(); i++)
01309     os << "    " << lits[i].getExpr() << "\n";
01310   os << "]\n  Gamma: [\n";
01311   for(size_t i=0; i<gamma.size(); i++)
01312     os << "    " << gamma[i].getExpr() << "\n";
01313   os << "]" << endl;
01314       })
01315       // Derive a theorem for the conflict clause
01316       Theorem clause = d_rules->conflictClause(start, lits, gamma);
01317       d_conflictClauseCount++;
01318       // Generate the actual clause and set it up
01319       Clause c(d_core, d_vm, clause, d_bottomScope, __FILE__, __LINE__);
01320       updateLitCounts(c);
01321       if (c.size() > 1) {
01322   // Set the watched pointers to the two literals with the
01323   // highest scopes
01324         int firstLit = 0;
01325         int secondLit = 1;
01326         int firstDL = c[0].getScope();
01327         int secondDL = c[1].getScope();
01328   // Invariant: firstDL >= secondDL
01329   if(firstDL < secondDL) {
01330     firstLit=1; secondLit=0;
01331     int tmp(secondDL);
01332     secondDL=firstDL; firstDL=tmp;
01333   }
01334   for(unsigned i = 2; i < c.size(); ++i) {
01335     int cur = c[i].getScope();
01336     if(cur >= firstDL) {
01337       secondLit=firstLit; secondDL=firstDL;
01338       firstLit=i; firstDL=cur;
01339     } else if(cur > secondDL) {
01340       secondLit=i; secondDL=cur;
01341     }
01342   }
01343 
01344         c.wp(0, firstLit);
01345         c.wp(1, secondLit);
01346     
01347         // Add the watch pointers to the d_wp lists
01348         for(int i=0; i<=1; i++) {
01349           // Negated watched literal
01350           Literal l(!c.watched(i));
01351           // Add the pointer to l's list
01352           pair<Clause, int> p(c, i);
01353           wp(l).push_back(p);
01354         }
01355       }
01356       TRACE("conflict clauses",
01357       "Conflict clause #"+int2string(d_conflictClauseCount)
01358       +": ", CompactClause(c), "");
01359       if(c.size() == 1) {
01360         // Unit clause: stash it for later unit propagation
01361         TRACE("conflict clauses", "analyzeUIPs(): unit clause: ",
01362               CompactClause(c), "");
01363         d_unitConflictClauses.push_back(c);
01364       }
01365       else {
01366         TRACE("conflict clauses", "analyzeUIPs(): conflict clause ",
01367         CompactClause(c), "");
01368         DebugAssert(c.getScope() <= d_bottomScope,
01369         "Conflict clause should be at bottom scope.");
01370         d_conflictClauses->push_back(c);
01371         if (d_lastConflictClause.isNull()) {
01372           d_lastConflictClause = c;
01373 //    IF_DEBUG(for(unsigned i=0; i<c.size(); ++i)
01374 //      DebugAssert(c[i].getValue() == -1, "Bad conflict clause: "
01375 //      +c.toString());)
01376   }
01377       }
01378       if(fringe[curr].size() > 0) {
01379   // This was a UIP.  Leave it in the fringe for later expansion.
01380   IF_DEBUG(debugger.counter("UIPs")++;)
01381   start = fringe[curr].back();
01382   lits.clear();
01383   gamma.clear();
01384   start.clearAllFlags();
01385       } else {
01386   // No more conflict clauses, we are done.  This is the only
01387   // way this function can return.
01388   TRACE_MSG("impl graph", "analyzeUIPs => }");
01389   return;
01390       }
01391     }
01392     // Now expand all the nodes in the fringe
01393     for(vector<Theorem>::iterator i=fringe[curr].begin(),
01394     iend=fringe[curr].end();
01395   i!=iend; ++i) {
01396       const Assumptions& a=i->getAssumptionsRef();
01397       for(Assumptions::iterator j=a.begin(), jend=a.end(); j!=jend; ++j) {
01398   processNode(*j, lits, gamma, fringe[next], pending);
01399       }
01400     }
01401     // Swap the current and next fringes
01402     fringe[curr].clear();
01403     curr = 1 - curr;
01404     next = 1 - next;
01405     IF_DEBUG(if(pending > 0 && fringe[curr].size()==0)
01406        falseThm.printDebug();)
01407     DebugAssert(pending == 0 || fringe[curr].size() > 0,
01408     "analyzeUIPs(scope = "
01409     +int2string(conflictScope)+"): empty fringe");
01410   }
01411 }
01412 
01413 
01414 ////////////////////////////////
01415 // End New Search Engine Code //
01416 ////////////////////////////////
01417 
01418 
01419 //! Redefine the counterexample generation.
01420 /*! FIXME: for now, it just dumps all the assumptions (same as
01421  * getAssumptions()).  Eventually, it will simplify the related
01422  * formulas to TRUE, merge all the generated assumptions into
01423  * d_lastCounterExample, and call the parent's method. */
01424 void SearchEngineFast::getCounterExample(std::vector<Expr>& assertions) {
01425   // This will not add anything, since the counterexample is empty,
01426   // but will check if we are allowed to be called
01427   SearchImplBase::getCounterExample(assertions);
01428   getAssumptions(assertions);
01429 }
01430 
01431 
01432 //! Notify the search engine about a new non-literal fact.
01433 /*! It should be called by TheoryCore::assertFactCore().
01434  *
01435  * If the fact is an AND, we split it into individual conjuncts and
01436  * add them individually.
01437  *
01438  * If the fact is an OR, we check whether it's a CNF clause; that is,
01439  * whether all disjuncts are literals.  If they are, we add it as a
01440  * CNF clause.
01441  *
01442  * Otherwise add the fact to d_nonLiterals as it is.
01443  */
01444 void
01445 SearchEngineFast::addNonLiteralFact(const Theorem& thm) {
01446   TRACE("search", "addNonLiteralFact(", thm, ") {");
01447   TRACE("search", "d_nonLiteralsSaved.size()=",d_nonLiteralsSaved.size(),
01448   "@"+int2string(scopeLevel()));
01449   //IF_DEBUG(checkAssumpDebug(thm, d_assumptions);)
01450   const Expr& e(thm.getExpr());
01451   if(d_nonLiteralsSaved.count(e) > 0) {
01452     // We've seen this non-literal before.
01453     TRACE_MSG("search", "addNonLiteralFact[skipping] => }");
01454     IF_DEBUG(debugger.counter("skipped repeated non-literals")++;)
01455     return;
01456   }
01457   // Save the non-literal
01458   d_nonLiteralsSaved[e]=thm;
01459   bool isCNFclause(false);
01460   // Split conjunctions into individual assertions and add them to the
01461   // appropriate lists
01462 
01463   int k = e.getKind();
01464   if (k == AND_R || k == IFF_R || k == ITE_R)
01465   {
01466     d_circuits.push_back(new Circuit(this, thm));
01467   }
01468 
01469   else if(e.isAnd()) {
01470     for(int i=0, iend=e.arity(); i<iend; ++i) {
01471       Theorem t_i(d_commonRules->andElim(thm, i));
01472       // Call enqueueFact(), not addFact(), since we are called from
01473       // addFact() here
01474       if(e[i].isAbsLiteral()) {
01475   d_core->enqueueFact(t_i);
01476       }
01477       else addNonLiteralFact(t_i);
01478     }
01479   } else {
01480     int unsetLits(0); // Count the number of unset literals
01481     size_t unitLit(0); // If the #unsetLits==1, this is the only unset literal
01482     vector<Theorem> thms; // collect proofs of !l_i for unit prop.
01483     if(e.isOr()) {
01484       isCNFclause = true;
01485       for(int i=0; isCNFclause && i<e.arity(); ++i) {
01486   isCNFclause=e[i].isAbsLiteral();
01487   if(isCNFclause) {
01488     // Check the value of the literal
01489     Literal l(newLiteral(e[i]));
01490     if(l.getValue() > 0) // The entire clause is true; ignore it
01491       return;
01492     if(l.getValue() == 0) { // Found unset literal
01493       unsetLits++; unitLit = i;
01494     } else // Literal is false, collect the theorem for it
01495       thms.push_back(l.deriveTheorem());
01496   }
01497       }
01498     }
01499     if(isCNFclause) {
01500       DebugAssert(e.arity() > 1, "Clause should have more than one literal");
01501       // Check if clause is unit or unsat
01502       if(unsetLits==0) { // Contradiction
01503   TRACE("search", "contradictory clause:\n",
01504         CompactClause(Clause(d_core, d_vm, thm, scopeLevel())),"");
01505   setInconsistent(d_rules->conflictRule(thms, thm));
01506       } else if(unsetLits==1) { // Unit clause: propagate literal
01507   TRACE("search", "unit clause, unitLit = "+int2string(unitLit)+":\n", 
01508         CompactClause(Clause(d_core, d_vm, thm, scopeLevel())),"");
01509   d_core->enqueueFact(d_rules->unitProp(thms, thm, unitLit));
01510       } else { // Wrap up the clause
01511   Clause c(d_core, d_vm, thm, scopeLevel(), __FILE__, __LINE__);
01512   IF_DEBUG(debugger.counter("CNF clauses added")++;)
01513   TRACE("search", "addNonLiteralFact: adding CNF: ", c, "");
01514   addNewClause(c);
01515       }
01516     } else {
01517       TRACE("search", "addNonLiteralFact: adding non-literal: ", thm, "");
01518       IF_DEBUG(debugger.counter("added non-literals")++;)
01519       d_nonLiterals.push_back(SmartCDO<Theorem>(d_core->getCM()->getCurrentContext(), thm));
01520       //      d_nonLiteralSimplified[thm.getExpr()] = false;
01521     }
01522   }
01523   TRACE_MSG("search", "addNonLiteralFact => }");
01524 }
01525 
01526 
01527 //! Notify the search engine about a new literal fact.
01528 /*! It should be called by TheoryCore::assertFactCore() */
01529 void
01530 SearchEngineFast::addLiteralFact(const Theorem& thm) {
01531   TRACE("search", "addLiteralFact(", thm, ")");
01532   // Save the value of the flag to restore it later
01533   bool useEF(d_useEnqueueFact);
01534   d_useEnqueueFact=true;
01535 
01536   DebugAssert(thm.isAbsLiteral(),
01537         "addLiteralFact: not a literal: " + thm.toString());
01538   //IF_DEBUG(checkAssumpDebug(thm, d_assumptions);)
01539   Literal l(newLiteral(thm.getExpr()));
01540   TRACE("search", "addLiteralFact: literal = ", l, "");
01541   // Only add the literal if it doesn't have any value; otherwise it's
01542   // either a contradiction, or it must already be in the list
01543   // FIXME: why did we need thm.getScope() != 0 ???
01544   if ((l.getValue() == 0 /* && thm.getScope() != 0 */)
01545       /* || (l.getValue() == 1 && l.getScope() > thm.getScope()) */) {
01546     l.setValue(thm, scopeLevel());
01547     DebugAssert(l.getExpr().isAbsLiteral(),
01548     "addLiteralFact(): pushing non-literal to d_literals:\n "
01549     +l.getExpr().toString());
01550     DebugAssert(l.getValue() == 1, "addLiteralFact(): l = "+l.toString());
01551     d_literals.push_back(l);
01552     d_literalSet.insert(l.getExpr(),l);
01553     // Immediately propagate the literal with BCP, unless the SAT
01554     // solver is already running
01555     if(!d_inCheckSAT) bcp();
01556 
01557 //     if (thm.getScope() != scopeLevel()) {
01558 //       IF_DEBUG(debugger.counter("addLiteralFact adds unreported lit")++;)
01559 //       d_unreportedLits.insert(l.getExpr(),thm,thm.getScope());
01560 //     }
01561   } else if(l.getValue() < 0) { // Contradiction, bcp will die anyway
01562     if(l.isNegative())
01563       setInconsistent(d_commonRules->contradictionRule(l.deriveTheorem(), thm));
01564     else
01565       setInconsistent(d_commonRules->contradictionRule(thm, l.deriveTheorem()));
01566   }
01567   d_useEnqueueFact=useEF;
01568 }
01569 
01570 /*! @brief Redefine newIntAssumption(): we need to add the new theorem
01571  * to the appropriate Literal */
01572 Theorem
01573 SearchEngineFast::newIntAssumption(const Expr& e) {
01574   Theorem thm(SearchImplBase::newIntAssumption(e));
01575   DebugAssert(thm.isAssump(), "Splitter should be an assumption:" + thm.toString());
01576   TRACE("search full", "Splitter: ", thm.toString(), "");
01577   const Expr& expr = thm.getExpr();
01578   Literal l(newLiteral(expr));
01579   if(l.getValue() == 0) {
01580     l.setValue(thm, scopeLevel());
01581     if(l.getExpr().isAbsLiteral()) {
01582       DebugAssert(l.getValue() == 1, "newIntAssumption(): l = "+l.toString());
01583       d_literals.push_back(l);
01584     }
01585     else
01586       d_litsAlive.push_back(l);
01587   }
01588 
01589     
01590   return thm;
01591 }
01592 
01593 bool 
01594 SearchEngineFast::isAssumption(const Expr& e) {
01595   return (SearchImplBase::isAssumption(e)
01596     || (d_nonLiteralsSaved.count(e) > 0));
01597 }
01598 
01599 
01600 void
01601 SearchEngineFast::addSplitter(const Expr& e, int priority) {
01602   // SearchEngine::addSplitter(e, priority);
01603   DebugAssert(e.isAbsLiteral(), "SearchEngineFast::addSplitter("+e.toString()+")");
01604   Literal lit(newLiteral(e));
01605   d_dpSplitters.push_back(Splitter(lit));
01606   if(priority != 0) {
01607     d_litSortCount--;
01608     lit.score() += priority*10;
01609   }
01610   if(!lit.added()) {
01611     TRACE("search literals", "addSplitter(): adding literal ", lit, " to d_litsByScores");
01612     d_litsByScores.push_back(lit);
01613     lit.added()=true;
01614     if(priority == 0) d_litSortCount--;
01615   }
01616   if(d_litSortCount < 0) {
01617     ::stable_sort(d_litsByScores.begin(), d_litsByScores.end(), compareLits);
01618     d_litSortCount=d_litsByScores.size();
01619   }
01620   TRACE("search splitters","addSplitter => ", lits2str(d_litsByScores),"");
01621 }
01622 
01623 
01624 QueryResult SearchEngineFast::checkValidMain(const Expr& e2)
01625 {
01626   // Propagate the literals asserted before checkValid()
01627   for(CDMap<Expr,Literal>::iterator i=d_literalSet.begin(),
01628   iend=d_literalSet.end(); i!=iend; ++i)
01629     d_literals.push_back((*i).second);
01630 
01631   // Run the SAT solver
01632   QueryResult result = checkSAT();
01633 
01634   Theorem res;
01635   if (result == UNSATISFIABLE)
01636     res = d_conflictTheorem;
01637   else if (result == SATISFIABLE) {
01638     // Set counter-example
01639     vector<Expr> a;
01640     unsigned i;
01641     Theorem thm;
01642 
01643     d_lastCounterExample.clear();
01644     for (i=d_nonlitQueryStart; i < d_nonlitQueryEnd; ++i) {
01645       thm = d_nonLiterals[i].get();
01646       DebugAssert(thm.getExpr().isTrue(),
01647                   "original nonLiteral doesn't simplify to true");
01648       thm.getLeafAssumptions(a);
01649       for (vector<Expr>::iterator i=a.begin(), iend=a.end(); i != iend; ++i) {
01650         d_lastCounterExample[*i] = true;
01651       }
01652       a.clear();
01653     }
01654     for (i=d_clausesQueryStart; i < d_clausesQueryEnd; ++i) {
01655       thm = simplify(((Clause)d_clauses[i]).getTheorem());
01656       DebugAssert(thm.getExpr().isTrue(),
01657                   "original nonLiteral doesn't simplify to true");
01658       thm.getLeafAssumptions(a);
01659       for (vector<Expr>::iterator i=a.begin(), iend=a.end(); i != iend; ++i) {
01660         d_lastCounterExample[*i] = true;
01661       }
01662       a.clear();
01663     }
01664   }
01665   else return result;
01666 
01667   processResult(res, e2);
01668 
01669   if (result == UNSATISFIABLE) {
01670     d_core->getCM()->popto(d_bottomScope);
01671     d_litsMaxScorePos = 0; // from decision engine
01672 
01673     // Clear data structures
01674     d_unitConflictClauses.clear();
01675     clearLiterals();
01676     clearFacts();
01677 
01678     Theorem e_iff_e2(d_commonRules->iffContrapositive(d_simplifiedThm));
01679     d_lastValid =
01680       d_commonRules->iffMP(d_lastValid, d_commonRules->symmetryRule(e_iff_e2));
01681     IF_DEBUG(checkAssumpDebug(d_lastValid, d_assumptions);)
01682     TRACE_MSG("search terse", "checkValid => true}");
01683     TRACE("search", "checkValid => true; theorem = ", d_lastValid, "}");
01684     d_core->getCM()->pop();
01685   }
01686   else {
01687     TRACE_MSG("search terse", "checkValid => false}");
01688     TRACE_MSG("search", "checkValid => false; }");
01689     DebugAssert(d_unitConflictClauses.size() == 0, "checkValid(): d_unitConflictClauses postcondition violated");
01690     DebugAssert(d_literals.size() == 0, "checkValid(): d_literals postcondition violated");
01691     DebugAssert(d_factQueue.empty(), "checkValid(): d_factQueue postcondition violated");
01692   }
01693   return result;
01694 }
01695 
01696 
01697 QueryResult SearchEngineFast::checkValidInternal(const Expr& e)
01698 {
01699   DebugAssert(d_unitConflictClauses.size() == 0, "checkValid(): d_unitConflitClauses precondition violated");
01700   DebugAssert(d_factQueue.empty(), "checkValid(): d_factQueue precondition violated");
01701 
01702   TRACE("search", "checkValid(", e, ") {");
01703   TRACE_MSG("search terse", "checkValid() {");
01704 
01705   if (!e.getType().isBool()) {
01706     throw TypecheckException
01707       ("checking validity of a non-boolean expression:\n\n  "
01708        + e.toString()
01709        + "\n\nwhich has the following type:\n\n  "
01710        + e.getType().toString());
01711   }
01712 
01713   // A successful query should leave the context unchanged
01714   d_core->getCM()->push();
01715   d_conflictClauseManager.setRestorePoint();
01716   d_bottomScope = scopeLevel();
01717 
01718   // First, simplify the NEGATION of the given expression: that's what
01719   // we'll assert
01720   d_simplifiedThm = d_core->getExprTrans()->preprocess(e.negate());
01721   TRACE("search", "checkValid: simplifiedThm = ", d_simplifiedThm, "");
01722 
01723   const Expr& not_e2 = d_simplifiedThm.get().getRHS();
01724   Expr e2 = not_e2.negate();
01725 
01726   // Assert not_e2 if it's not already asserted
01727   TRACE_MSG("search terse", "checkValid: Asserting !e: ");
01728   TRACE("search", "checkValid: Asserting !e: ", not_e2, "");
01729   Theorem not_e2_thm;
01730   d_nonlitQueryStart = d_nonLiterals.size();
01731   d_clausesQueryStart = d_clauses.size();
01732   if(d_assumptions.count(not_e2) == 0) {
01733     not_e2_thm = newUserAssumption(not_e2);
01734   } else {
01735     not_e2_thm = d_assumptions[not_e2];
01736   }
01737   //  d_core->addFact(not_e2_thm);
01738   d_nonlitQueryEnd = d_nonLiterals.size();
01739   d_clausesQueryEnd = d_clauses.size();
01740 
01741   // Reset the splitter counter.  This will force a call to
01742   // updateLitScores() the first time we need to find a splitter, and
01743   // clean out junk from the previous calls to checkValid().
01744   d_splitterCount=0;
01745 
01746   return checkValidMain(e2);
01747 }
01748 
01749 
01750 QueryResult SearchEngineFast::restartInternal(const Expr& e)
01751 {
01752   DebugAssert(d_unitConflictClauses.size() == 0, "restart(): d_unitConflitClauses precondition violated");
01753   DebugAssert(d_factQueue.empty(), "restart(): d_factQueue precondition violated");
01754 
01755   TRACE("search", "restart(", e, ") {");
01756   TRACE_MSG("search terse", "restart() {");
01757 
01758   if (!e.getType().isBool()) {
01759     throw TypecheckException
01760       ("argument to restart is a non-boolean expression:\n\n  "
01761        + e.toString()
01762        + "\n\nwhich has the following type:\n\n  "
01763        + e.getType().toString());
01764   }
01765 
01766   if (d_bottomScope == 0) {
01767     throw Exception("Call to restart with no current query");
01768   }
01769   d_core->getCM()->popto(d_bottomScope);
01770 
01771   Expr e2 = d_simplifiedThm.get().getRHS().negate();
01772 
01773   TRACE_MSG("search terse", "restart: Asserting e: ");
01774   TRACE("search", "restart: Asserting e: ", e, "");
01775   if(d_assumptions.count(e) == 0) {
01776     d_core->addFact(newUserAssumption(e));
01777   }
01778 
01779   return checkValidMain(e2);
01780 }
01781 
01782 /*!
01783  * The purpose of this method is to mark up the assumption graph of
01784  * the FALSE Theorem (conflictThm) for the later UIP analysis.  The
01785  * required flags for each assumption in the graph are:
01786  *
01787  * <strong>ExpandFlag:</strong> whether to "expand" the node or not;
01788  * that is, whether to consider the current node as a final assumption
01789  * (either as a conflict clause literal, or a context assumption from
01790  * \f$\Gamma\f$)
01791  *
01792  * <strong>LitFlag:</strong> the node (actually, its inverse) is a
01793  * literal of the conflict clause
01794  *
01795  * <strong>CachedValue:</strong> the "fanout" count, how many nodes in
01796  * the assumption graph are derived from the current node.
01797  * 
01798  * INVARIANTS (after the method returns):
01799  *
01800  * -# The currect scope is the "true" conflict scope,
01801  *    i.e. scopeLevel() == conflictThm.getScope()
01802  * -# The literals marked with LitFlag (CC literals) are known to the
01803  *    SAT solver, i.e. their Literal class has a value == 1
01804  * -# The only CC literal from the current scope is the latest splitter
01805  *
01806  * ASSUMPTIONS: 
01807  * 
01808  * -# The Theorem scope of an assumption is the same as its Literal scope;
01809  *    i.e. if thm is a splitter, then 
01810  *    thm.getScope() == newLiteral(thm.getExpr()).getScope()
01811  *
01812  * Algorithm:
01813  * 
01814  * First, backtrack to the scope level of the conflict.  Then,
01815  * traverse the implication graph until we either hit a literal known
01816  * to the SAT solver at a lower scope:
01817  * newLiteral(e).getScope()<scopeLevel(), or a splitter (assumption), or a
01818  * fact from the bottom scope.  The literals from the first two
01819  * categories are marked with LitFlag (they'll comprise the conflict
01820  * clause), and the bottom scope facts will be the assumptions in the
01821  * conflict clause's theorem.
01822  *
01823  * The traversed nodes are cached by the .isFlagged() flag, and
01824  * subsequent hits only increase the fanout count of the node.
01825  *
01826  * Notice, that there can only be one literal in the conflict clause
01827  * from the current scope.  Also, even if some intermediate literals
01828  * were delayed by the DPs and reported to the SAT solver at or below
01829  * the conflict scope (which may be below their "true" Theorem scope),
01830  * they will be skipped, and their assumptions will be used.
01831  *
01832  * In other words, it is safe to backtrack to the "true" conflict
01833  * level, since, in the worst case, we traverse the graph all the way
01834  * to the splitters, and make a conflict clause out of those.  The
01835  * hope is, however, that this wouldn't happen too often.
01836  */
01837 void SearchEngineFast::traceConflict(const Theorem& conflictThm) {
01838   TRACE("impl graph", "traceConflict(", conflictThm.getExpr(), ") {");
01839   
01840   // Always process conflict at its true scope or the bottom scope,
01841   // whichever is greater.
01842   DebugAssert(conflictThm.getScope() <= scopeLevel(),
01843         "conflictThm.getScope()="+int2string(conflictThm.getScope())
01844         +", scopeLevel()="+int2string(scopeLevel()));
01845   if(conflictThm.getScope() < scopeLevel()) {
01846     int scope(conflictThm.getScope());
01847     if(scope < d_bottomScope) scope = d_bottomScope;
01848     d_decisionEngine->popTo(scope);
01849   }
01850 
01851   if(scopeLevel() <= d_bottomScope) {
01852     // This is a top-level conflict, nothing to analyze.
01853     TRACE_MSG("impl graph", "traceConflict[bottom scope] => }");
01854     return;
01855   }
01856 
01857   // DFS stack
01858   vector<Theorem> stack;
01859   // Max assumption scope for the contradiction
01860   int maxScope(d_bottomScope);
01861   // Collect potential top-level splitters
01862   IF_DEBUG(vector<Theorem> splitters;)
01863   TRACE("impl graph", "traceConflict: maxScope = ", maxScope, "");
01864 
01865   conflictThm.clearAllFlags();
01866   conflictThm.setExpandFlag(true);
01867   conflictThm.setCachedValue(0);
01868 
01869   const Assumptions& assump = conflictThm.getAssumptionsRef();
01870   for(Assumptions::iterator i=assump.begin(),iend=assump.end();i!=iend;++i) {
01871     TRACE("impl graph", "traceConflict: adding ", *i, "");
01872     stack.push_back(*i);
01873   }
01874 
01875   // Do the non-recursive DFS, mark up the assumption graph
01876   IF_DEBUG(Literal maxScopeLit;)
01877   while(stack.size() > 0) {
01878     Theorem thm(stack.back());
01879     stack.pop_back();
01880     TRACE("impl graph", "traceConflict: while() { thm = ", thm, "");
01881     if (thm.isFlagged()) {
01882       // We've seen this theorem before.  Update fanout count.
01883       thm.setCachedValue(thm.getCachedValue() + 1);
01884       TRACE("impl graph", "Found again: ", thm.getExpr().toString(), "");
01885       TRACE("impl graph", "With fanout: ", thm.getCachedValue(), "");
01886     }
01887     else {
01888       // This is a new theorem.  Process it.
01889       thm.setCachedValue(1);
01890       thm.setFlag();
01891       thm.setLitFlag(false); // Clear this flag (it may be set later)
01892       bool expand(false);
01893       int scope = thm.getScope();
01894       bool isAssump = thm.isAssump();
01895 
01896       IF_DEBUG({
01897   int s = scope;
01898   if(thm.isAbsLiteral()) {
01899     Literal l(newLiteral(thm.getExpr()));
01900     if(l.getValue() == 1) s = l.getScope();
01901   }
01902   // maxScope will be reset: clear the splitters
01903   if(s > maxScope) splitters.clear();
01904       })
01905 
01906       if(thm.isAbsLiteral()) {
01907   Literal l(newLiteral(thm.getExpr()));
01908   bool isTrue(l.getValue()==1);
01909   if(isTrue) scope = l.getScope();
01910   if(!isAssump && (!isTrue || scope == scopeLevel()))
01911     expand=true;
01912   else if(scope > d_bottomScope) {// Found a literal of a conflict clause
01913     IF_DEBUG(if(scope >= maxScope) splitters.push_back(thm);)
01914     thm.setLitFlag(true);
01915   }
01916       } else {
01917   DebugAssert(scope <= d_bottomScope || !isAssump,
01918         "SearchEngineFast::traceConflict: thm = "
01919         +thm.toString());
01920   if(!isAssump && scope > d_bottomScope)
01921     expand=true;
01922       }
01923 
01924       if(scope > maxScope) {
01925   maxScope = scope;
01926   IF_DEBUG(maxScopeLit = newLiteral(thm.getExpr());)
01927   TRACE("impl graph", "traceConflict: maxScope = ", maxScope, "");
01928       }
01929 
01930       if(expand) {
01931   DebugAssert(!thm.isAssump(),
01932         "traceConflict: thm = "+thm.toString());
01933   thm.setExpandFlag(true);
01934   const Assumptions& assump = thm.getAssumptionsRef();
01935   for(Assumptions::iterator i=assump.begin(),iend=assump.end();
01936       i!=iend; ++i) {
01937     TRACE("impl graph", "traceConflict: adding ", *i, "");
01938     stack.push_back(*i);
01939   }
01940       } else
01941   thm.setExpandFlag(false);
01942     }
01943     TRACE_MSG("impl graph", "traceConflict: end of while() }");
01944   }
01945   IF_DEBUG(if(maxScope != scopeLevel()) conflictThm.printDebug();)
01946   DebugAssert(maxScope == scopeLevel(), "maxScope="+int2string(maxScope)
01947         +", scopeLevel()="+int2string(scopeLevel())
01948         +"\n maxScopeLit = "+maxScopeLit.toString());
01949   IF_DEBUG(
01950     if(!(maxScope == d_bottomScope || splitters.size() == 1)) {
01951       conflictThm.printDebug();
01952       ostream& os = debugger.getOS();
01953       os << "\n\nsplitters = [";
01954       for(size_t i=0; i<splitters.size(); ++i)
01955   os << splitters[i] << "\n";
01956       os << "]" << endl;
01957     }
01958     )
01959   DebugAssert(maxScope == d_bottomScope || splitters.size() == 1,
01960           "Wrong number of splitters found at maxScope="
01961           +int2string(maxScope)
01962           +": "+int2string(splitters.size())+" splitters.");
01963   d_lastConflictScope = maxScope;
01964   analyzeUIPs(conflictThm, maxScope);
01965   TRACE_MSG("impl graph", "traceConflict => }");
01966 }

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