Solver: Keep track of a solution's score as we're computing it.

No functionality change here; just staging for some future optimizations.


Swift SVN r11028

lib/Sema/CSApply.cpp

@@ -3353,54 +3353,3 @@ Solution::convertToArrayBound(Expr *expr, ConstraintLocator *locator) const {
   
   return result;
 }
-
-int Solution::getFixedScore() const {
-  if (fixedScore)
-    return *fixedScore;
-
-  int score = 0;
-
-  // Consider overload choices.
-  for (auto overload : overloadChoices) {
-    auto choice = overload.second.choice;
-    if (choice.getKind() != OverloadChoiceKind::Decl)
-      continue;
-
-    // -3 penalty for each user-defined conversion.
-    if (choice.getDecl()->getAttrs().isConversion())
-      score -= 3;
-  }
-
-  // Consider type bindings.
-  auto &tc = getConstraintSystem().getTypeChecker();
-  for (auto binding : typeBindings) {
-    // Look for type variables corresponding directly to an expression.
-    auto typeVar = binding.first;
-    auto locator = typeVar->getImpl().getLocator();
-    if (!locator || !locator->getAnchor() || !locator->getPath().empty())
-      continue;
-
-    // Check whether there is a literal protocol corresponding to the
-    // anchor expression.
-    auto literalProtocol
-      = tc.getLiteralProtocol(locator->getAnchor());
-    if (!literalProtocol)
-      continue;
-
-    // Retrieve the default type for this literal protocol, if there is one.
-    auto defaultType = tc.getDefaultType(literalProtocol,
-                                         getConstraintSystem().DC);
-    if (!defaultType)
-      continue;
-
-    // +1 if the bound type matches the default type for this literal protocol.
-    // Literal types are always nominal, so we simply check the nominal
-    // declaration. This covers e.g., Slice vs. Slice<T>.
-    if (defaultType->getAnyNominal() == binding.second->getAnyNominal())
-      ++score;
-  }
-
-  // Save the fixed score.
-  fixedScore = score;
-  return score;
-}

lib/Sema/CSRanking.cpp

@@ -27,6 +27,20 @@ using namespace constraints;
 #define DEBUG_TYPE "Constraint solver overall"
 STATISTIC(NumDiscardedSolutions, "# of solutions discarded");
 
+void ConstraintSystem::increaseScore(ScoreKind kind) {
+  unsigned index = static_cast<unsigned>(kind);
+  ++CurrentScore.Data[index];
+}
+
+llvm::raw_ostream &constraints::operator<<(llvm::raw_ostream &out,
+                                           const Score &score) {
+  for (unsigned i = 0; i != NumScoreKinds; ++i) {
+    if (i) out << ' ';
+    out << score.Data[i];
+  }
+  return out;
+}
+
 /// \brief Remove the initializers from any tuple types within the
 /// given type.
 static Type stripInitializers(TypeChecker &tc, Type origType) {
@@ -446,6 +460,13 @@ Comparison TypeChecker::compareDeclarations(DeclContext *dc,
   return decl1Better? Comparison::Better : Comparison::Worse;
 }
 
+/// Simplify a score into a single integer.
+/// FIXME: Temporary hack.
+static int simplifyScore(const Score &score) {
+  return (int)score.Data[SK_UserConversion] * -3
+      + (int)score.Data[SK_NonDefaultLiteral] * -1;
+}
+
 SolutionCompareResult ConstraintSystem::compareSolutions(
                         ConstraintSystem &cs,
                         ArrayRef<Solution> solutions,
@@ -458,8 +479,8 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
   // Solution comparison uses a scoring system to determine whether one
   // solution is better than the other. Retrieve the fixed scores for each of
   // the solutions, which we'll modify with relative scoring.
-  int score1 = solutions[idx1].getFixedScore();
-  int score2 = solutions[idx2].getFixedScore();
+  int score1 = simplifyScore(solutions[idx1].getFixedScore());
+  int score2 = simplifyScore(solutions[idx2].getFixedScore());
 
   // Compare overload sets.
   for (auto &overload : diff.overloads) {

lib/Sema/CSSimplify.cpp

@@ -526,6 +526,9 @@ tryUserConversion(ConstraintSystem &cs, Type type, ConstraintKind kind,
     cs.addConstraint(kind, outputTV, otherType, resultLocator);
   }
 
+  // We're adding a user-defined conversion.
+  cs.increaseScore(SK_UserConversion);
+
   return ConstraintSystem::SolutionKind::Solved;
 }
 

lib/Sema/CSSolver.cpp

@@ -73,7 +73,7 @@ static Optional<Type> checkTypeOfBinding(ConstraintSystem &cs,
 Solution ConstraintSystem::finalize(
            FreeTypeVariableBinding allowFreeTypeVariables) {
   // Create the solution.
-  Solution solution(*this);
+  Solution solution(*this, CurrentScore);
 
   // For any of the type variables that has no associated fixed type, assign a
   // fresh generic type parameters.
@@ -123,6 +123,9 @@ Solution ConstraintSystem::finalize(
 }
 
 void ConstraintSystem::applySolution(const Solution &solution) {
+  // Update the score.
+  CurrentScore += solution.getFixedScore();
+
   // Assign fixed types to the type variables solved by this solution.
   llvm::SmallPtrSet<TypeVariableType *, 4> 
     knownTypeVariables(TypeVariables.begin(), TypeVariables.end());
@@ -134,7 +137,7 @@ void ConstraintSystem::applySolution(const Solution &solution) {
     // If we don't already have a fixed type for this type variable,
     // assign the fixed type from the solution.
     if (!getFixedType(binding.first) && !binding.second->hasTypeVariable())
-      assignFixedType(binding.first, binding.second);
+      assignFixedType(binding.first, binding.second, /*updateScore=*/false);
   }
 
   // Register overload choices.
@@ -583,6 +586,7 @@ ConstraintSystem::SolverScope::SolverScope(ConstraintSystem &cs)
   numConstraintRestrictions = cs.solverState->constraintRestrictions.size();
   oldGeneratedConstraints = cs.solverState->generatedConstraints;
   cs.solverState->generatedConstraints = &generatedConstraints;
+  PreviousScore = cs.CurrentScore;
 
   ++cs.solverState->NumStatesExplored;
 
@@ -618,6 +622,9 @@ ConstraintSystem::SolverScope::~SolverScope() {
   // Reset the prior generated-constraints pointer.
   cs.solverState->generatedConstraints = oldGeneratedConstraints;
 
+  // Reset the previous score.
+  cs.CurrentScore = PreviousScore;
+
   // Clear out other "failed" state.
   cs.failedConstraint = nullptr;
 }
@@ -932,7 +939,8 @@ bool ConstraintSystem::solve(SmallVectorImpl<Solution> &solutions,
     auto solution = finalize(allowFreeTypeVariables);
     if (TC.getLangOpts().DebugConstraintSolver) {
       auto &log = getASTContext().TypeCheckerDebug->getStream();
-      log.indent(solverState->depth * 2) << "(found solution)\n";
+      log.indent(solverState->depth * 2)
+        << "(found solution " << CurrentScore << ")\n";
     }
 
     solutions.push_back(std::move(solution));
@@ -1069,6 +1077,11 @@ bool ConstraintSystem::solve(SmallVectorImpl<Solution> &solutions,
     // Move the type variables back, clear out constraints; we're
     // ready for the next component.
     TypeVariables = std::move(allTypeVariables);
+
+    // For each of the partial solutions, substract off the current score.
+    // It doesn't contribute.
+    for (auto &solution : partialSolutions[component])
+      solution.getFixedScore() -= CurrentScore;
   }
 
   // Move the constraints back. The system is back in a normal state.
@@ -1103,7 +1116,8 @@ bool ConstraintSystem::solve(SmallVectorImpl<Solution> &solutions,
     auto solution = finalize(allowFreeTypeVariables);
     if (TC.getLangOpts().DebugConstraintSolver) {
       auto &log = getASTContext().TypeCheckerDebug->getStream();
-      log.indent(solverState->depth * 2) << "(composed solution)\n";
+      log.indent(solverState->depth * 2)
+        << "(composed solution " << CurrentScore << ")\n";
     }
 
     // Save this solution.

lib/Sema/ConstraintSystem.cpp

@@ -69,9 +69,51 @@ void ConstraintSystem::mergeEquivalenceClasses(TypeVariableType *typeVar1,
   }
 }
 
-void ConstraintSystem::assignFixedType(TypeVariableType *typeVar, Type type) {
+void ConstraintSystem::assignFixedType(TypeVariableType *typeVar, Type type,
+                                       bool updateScore) {
   typeVar->getImpl().assignFixedType(type, getSavedBindings());
 
+  if (updateScore && !type->is<TypeVariableType>()) {
+    // If this type variable represents a literal, check whether we picked the
+    // default literal type. First, find the corresponding protocol.
+    ProtocolDecl *literalProtocol = nullptr;
+    if (CG) {
+      // If we have the constraint graph, we can check all type variables in
+      // the equivalence class. This is the More Correct path.
+      // FIXME: Eliminate the less-correct path.
+      auto typeVarRep = getRepresentative(typeVar);
+      for (auto tv : (*CG)[typeVarRep].getEquivalenceClass()) {
+        auto locator = tv->getImpl().getLocator();
+        if (!locator || !locator->getPath().empty())
+          continue;
+
+        auto anchor = locator->getAnchor();
+        if (!anchor)
+          continue;
+
+        literalProtocol = TC.getLiteralProtocol(anchor);
+        if (literalProtocol)
+          break;
+      }
+    } else {
+      // FIXME: This is the less-correct path.
+      auto locator = typeVar->getImpl().getLocator();
+      if (locator && locator->getPath().empty() && locator->getAnchor()) {
+        literalProtocol = TC.getLiteralProtocol(locator->getAnchor());
+      }
+    }
+
+    // If the protocol has a default type, check it.
+    if (literalProtocol) {
+      if (auto defaultType = TC.getDefaultType(literalProtocol, DC)) {
+        // Check whether the nominal types match. This makes sure that we
+        // properly handle Slice vs. Slice<T>.
+        if (defaultType->getAnyNominal() != type->getAnyNominal())
+          increaseScore(SK_NonDefaultLiteral);
+      }
+    }
+  }
+
   // Notify the constraint graph.
   if (CG) {
     CG->bindTypeVariable(typeVar, type);

lib/Sema/ConstraintSystem.h

@@ -611,6 +611,94 @@ struct SelectedOverload {
   Type openedType;
 };
 
+/// Describes an aspect of a solution that affects is overall score, i.e., a
+/// user-defined conversions.
+enum ScoreKind {
+  /// A user-defined conversion.
+  SK_UserConversion = 0,
+  /// A literal expression bound to a non-default literal type.
+  SK_NonDefaultLiteral = 1
+};
+
+/// The number of score kinds.
+const unsigned NumScoreKinds = 2;
+
+/// Describes the fixed score of a solution to the constraint system.
+struct Score {
+  unsigned Data[NumScoreKinds] = { 0, 0 };
+
+  friend Score &operator+=(Score &x, const Score &y) {
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      x.Data[i] += y.Data[i];
+    }
+    return x;
+  }
+
+  friend Score operator+(const Score &x, const Score &y) {
+    Score result;
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      result.Data[i] = x.Data[i] + y.Data[i];
+    }
+    return result;
+  }
+
+  friend Score operator-(const Score &x, const Score &y) {
+    Score result;
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      result.Data[i] = x.Data[i] - y.Data[i];
+    }
+    return result;
+  }
+
+  friend Score &operator-=(Score &x, const Score &y) {
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      x.Data[i] -= y.Data[i];
+    }
+    return x;
+  }
+
+  friend bool operator==(const Score &x, const Score &y) {
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      if (x.Data[i] != y.Data[i])
+        return false;
+    }
+
+    return true;
+  }
+
+  friend bool operator!=(const Score &x, const Score &y) {
+    return !(x == y);
+  }
+
+  friend bool operator<(const Score &x, const Score &y) {
+    for (unsigned i = 0; i != NumScoreKinds; ++i) {
+      if (x.Data[i] < y.Data[i])
+        return true;
+
+      if (x.Data[i] > y.Data[i])
+        return false;
+    }
+
+    return true;
+  }
+
+  friend bool operator<=(const Score &x, const Score &y) {
+    return !(y < x);
+  }
+
+  friend bool operator>(const Score &x, const Score &y) {
+    return y < x;
+  }
+
+  friend bool operator>=(const Score &x, const Score &y) {
+    return !(x < y);
+  }
+
+};
+
+/// Display a score.
+llvm::raw_ostream &operator<<(llvm::raw_ostream &out, const Score &score);
+
 /// \brief A complete solution to a constraint system.
 ///
 /// A solution to a constraint system consists of type variable bindings to
@@ -622,31 +710,19 @@ class Solution {
   ConstraintSystem *constraintSystem;
 
   /// \brief The fixed score for this solution.
-  mutable Optional<int> fixedScore;
+  Score FixedScore;
 
 public:
   /// \brief Create a solution for the given constraint system.
-  Solution(ConstraintSystem &cs) : constraintSystem(&cs) {}
+  Solution(ConstraintSystem &cs, const Score &score)
+    : constraintSystem(&cs), FixedScore(score) {}
 
   // Solution is a non-copyable type for performance reasons.
   Solution(const Solution &other) = delete;
   Solution &operator=(const Solution &other) = delete;
 
-  Solution(Solution &&other)
-    : constraintSystem(other.constraintSystem),
-      typeBindings(std::move(other.typeBindings)),
-      overloadChoices(std::move(other.overloadChoices)),
-      constraintRestrictions(std::move(other.constraintRestrictions))
-  {
-  }
-
-  Solution &operator=(Solution &&other) {
-    constraintSystem = other.constraintSystem;
-    typeBindings = std::move(other.typeBindings);
-    overloadChoices = std::move(other.overloadChoices);
-    constraintRestrictions = std::move(other.constraintRestrictions);
-    return *this;
-  }
+  Solution(Solution &&other) = default;
+  Solution &operator=(Solution &&other) = default;
 
   /// \brief Retrieve the constraint system that this solution solves.
   ConstraintSystem &getConstraintSystem() const { return *constraintSystem; }
@@ -726,9 +802,11 @@ public:
                             Type openedType,
                             SmallVectorImpl<Substitution> &substitutions) const;
 
-  /// \brief Retrieve the fixed score of this solution, which considers
-  /// the number of user-defined conversions.
-  int getFixedScore() const;
+  /// \brief Retrieve the fixed score of this solution
+  const Score &getFixedScore() const { return FixedScore; }
+
+  /// \brief Retrieve the fixed score of this solution
+  Score &getFixedScore() { return FixedScore; }
 
   /// \brief Retrieve the fixed type for the given type variable.
   Type getFixedType(TypeVariableType *typeVar) const;
@@ -911,6 +989,10 @@ private:
   /// \brief The overload sets that have been resolved along the current path.
   ResolvedOverloadSetListItem *resolvedOverloadSets = nullptr;
 
+  /// The current fixed score for this constraint system and the (partial)
+  /// solution it represents.
+  Score CurrentScore;
+
   SmallVector<TypeVariableType *, 16> TypeVariables;
   ConstraintList Constraints;
 
@@ -1012,6 +1094,9 @@ public:
     /// \brief The length of \c constraintRestrictions.
     unsigned numConstraintRestrictions;
 
+    /// The previous score.
+    Score PreviousScore;
+
     /// Constraint graph scope associated with this solver scope.
     ///
     /// FIXME: This is optional so we can easily enabled/disable the
@@ -1314,7 +1399,12 @@ public:
                              bool wantRValue);
 
   /// \brief Assign a fixed type to the given type variable.
-  void assignFixedType(TypeVariableType *typeVar, Type type);
+  ///
+  /// \param typeVar The type variable to bind.
+  /// \param type The fixed type to which the type variable will be bound.
+  /// \param updateScore Whether to update the score based on this binding.
+  void assignFixedType(TypeVariableType *typeVar, Type type,
+                       bool updateScore = true);
 
 private:
   /// Introduce the constraints associated with the given type variable
@@ -1720,6 +1810,10 @@ private:
                                                 unsigned idx2);
 
 public:
+  /// Increase the score of the given kind for the current (partial) solution
+  /// along the.
+  void increaseScore(ScoreKind kind);
+
   /// \brief Given a set of viable solutions, find the best
   /// solution.
   ///

lib/Sema/TypeCheckConstraints.cpp

@@ -1504,7 +1504,8 @@ void Solution::dump(SourceManager *sm) const {
 }
 
 void Solution::dump(SourceManager *sm, raw_ostream &out) const {
-  out << "Fixed score: " << getFixedScore() << "\n\n";
+  out << "Fixed score: " << FixedScore << "\n";
+
   out << "Type variables:\n";
   for (auto binding : typeBindings) {
     out.indent(2);
@@ -1552,6 +1553,7 @@ void ConstraintSystem::dump() {
 }
 
 void ConstraintSystem::dump(raw_ostream &out) {
+  out << "Score: " << CurrentScore << "\n";
   out << "Type Variables:\n";
   for (auto tv : TypeVariables) {
     out.indent(2);

lib/Sema/TypeChecker.cpp

@@ -111,6 +111,7 @@ ProtocolDecl *TypeChecker::getLiteralProtocol(Expr *expr) {
   if (isa<InterpolatedStringLiteralExpr>(expr))
     return getProtocol(expr->getLoc(),
                        KnownProtocolKind::StringInterpolationConvertible);
+
   if (auto E = dyn_cast<MagicIdentifierLiteralExpr>(expr)) {
     switch (E->getKind()) {
     case MagicIdentifierLiteralExpr::File:
@@ -124,7 +125,7 @@ ProtocolDecl *TypeChecker::getLiteralProtocol(Expr *expr) {
     }
   }
   
-  llvm_unreachable("Unhandled literal kind");
+  return nullptr;
 }
 
 Module *TypeChecker::getStdlibModule(const DeclContext *dc) {