Sema: Mostly remove one-way constraints

include/swift/Sema/Constraint.h

@@ -857,11 +857,6 @@ class Constraint final : public llvm::ilist_node<Constraint>,
   /// from the rest of the constraint system.
   bool isIsolated() const { return IsIsolated; }
 
-  /// Whether this is a one-way constraint.
-  bool isOneWayConstraint() const {
-    return Kind == ConstraintKind::OneWayEqual;
-  }
-
   /// Retrieve the overload choice for an overload-binding constraint.
   OverloadChoice getOverloadChoice() const {
     assert(Kind == ConstraintKind::BindOverload);

include/swift/Sema/ConstraintGraph.h

@@ -295,25 +295,18 @@ class ConstraintGraph {
   /// to a type variable.
   void introduceToInference(TypeVariableType *typeVar, Type fixedType);
 
-  /// Describes which constraints \c gatherConstraints should gather.
-  enum class GatheringKind {
-    /// Gather constraints associated with all of the variables within the
-    /// same equivalence class as the given type variable, as well as its
-    /// immediate fixed bindings.
-    EquivalenceClass,
-    /// Gather all constraints that mention this type variable or type variables
-    /// that it is a fixed binding of. Unlike EquivalenceClass, this looks
-    /// through transitive fixed bindings. This can be used to find all the
-    /// constraints that may be affected when binding a type variable.
-    AllMentions,
-  };
+  /// Gather constraints associated with all of the variables within the
+  /// same equivalence class as the given type variable, as well as its
+  /// immediate fixed bindings.
+  llvm::TinyPtrVector<Constraint *>
+  gatherAllConstraints(TypeVariableType *typeVar);
 
-  /// Gather the set of constraints that involve the given type variable,
-  /// i.e., those constraints that will be affected when the type variable
-  /// gets merged or bound to a fixed type.
+  /// Gather all constraints that mention this type variable or type variables
+  /// that it is a fixed binding of. Unlike EquivalenceClass, this looks
+  /// through transitive fixed bindings. This can be used to find all the
+  /// constraints that may be affected when binding a type variable.
   llvm::TinyPtrVector<Constraint *>
-  gatherConstraints(TypeVariableType *typeVar,
-                    GatheringKind kind,
+  gatherNearbyConstraints(TypeVariableType *typeVar,
                     llvm::function_ref<bool(Constraint *)> acceptConstraint =
                         [](Constraint *constraint) { return true; });
 
@@ -338,12 +331,6 @@ class ConstraintGraph {
     /// The constraints in this component.
     TinyPtrVector<Constraint *> constraints;
 
-    /// The set of components that this component depends on, such that
-    /// the partial solutions of the those components need to be available
-    /// before this component can be solved.
-    ///
-    SmallVector<unsigned, 2> dependencies;
-
   public:
     Component(unsigned solutionIndex) : solutionIndex(solutionIndex) { }
 
@@ -359,11 +346,6 @@ class ConstraintGraph {
       return constraints;
     }
 
-    /// Records a component which this component depends on.
-    void recordDependency(const Component &component);
-
-    ArrayRef<unsigned> getDependencies() const { return dependencies; }
-
     unsigned getNumDisjunctions() const { return numDisjunctions; }
   };
 

lib/Sema/CSGen.cpp

@@ -400,8 +400,8 @@ namespace {
 
     llvm::SmallSetVector<ProtocolDecl *, 2> literalProtos;
     if (auto argTypeVar = argTy->getAs<TypeVariableType>()) {
-      auto constraints = CS.getConstraintGraph().gatherConstraints(
-          argTypeVar, ConstraintGraph::GatheringKind::EquivalenceClass,
+      auto constraints = CS.getConstraintGraph().gatherNearbyConstraints(
+          argTypeVar,
           [](Constraint *constraint) {
             return constraint->getKind() == ConstraintKind::LiteralConformsTo;
           });

lib/Sema/CSSimplify.cpp

@@ -15953,8 +15953,8 @@ ConstraintSystem::addKeyPathApplicationRootConstraint(Type root, ConstraintLocat
   if (!typeVar)
     return;
 
-  auto constraints = CG.gatherConstraints(
-      typeVar, ConstraintGraph::GatheringKind::EquivalenceClass,
+  auto constraints = CG.gatherNearbyConstraints(
+      typeVar,
       [&keyPathExpr](Constraint *constraint) -> bool {
         if (constraint->getKind() != ConstraintKind::KeyPath)
           return false;

lib/Sema/CSSolver.cpp

@@ -1876,8 +1876,8 @@ static Constraint *selectBestBindingDisjunction(
     if (!firstBindDisjunction)
       firstBindDisjunction = disjunction;
 
-    auto constraints = cs.getConstraintGraph().gatherConstraints(
-        typeVar, ConstraintGraph::GatheringKind::EquivalenceClass,
+    auto constraints = cs.getConstraintGraph().gatherNearbyConstraints(
+        typeVar,
         [](Constraint *constraint) {
           return constraint->getKind() == ConstraintKind::Conversion;
         });
@@ -1906,8 +1906,8 @@ ConstraintSystem::findConstraintThroughOptionals(
   while (visitedVars.insert(rep).second) {
     // Look for a disjunction that binds this type variable to an overload set.
     TypeVariableType *optionalObjectTypeVar = nullptr;
-    auto constraints = getConstraintGraph().gatherConstraints(
-        rep, ConstraintGraph::GatheringKind::EquivalenceClass,
+    auto constraints = getConstraintGraph().gatherNearbyConstraints(
+        rep,
         [&](Constraint *match) {
           // If we have an "optional object of" constraint, we may need to
           // look through it to find the constraint we're looking for.
@@ -2549,9 +2549,8 @@ void DisjunctionChoice::propagateConversionInfo(ConstraintSystem &cs) const {
     }
   }
 
-  auto constraints = cs.CG.gatherConstraints(
+  auto constraints = cs.CG.gatherNearbyConstraints(
       typeVar,
-      ConstraintGraph::GatheringKind::EquivalenceClass,
       [](Constraint *constraint) -> bool {
         switch (constraint->getKind()) {
         case ConstraintKind::Conversion:

lib/Sema/CSStep.cpp

@@ -126,7 +126,6 @@ void SplitterStep::computeFollowupSteps(
   // Take the orphaned constraints, because they'll go into a component now.
   OrphanedConstraints = CG.takeOrphanedConstraints();
 
-  IncludeInMergedResults.resize(numComponents, true);
   Components.resize(numComponents);
   PartialSolutions = std::unique_ptr<SmallVector<Solution, 4>[]>(
       new SmallVector<Solution, 4>[numComponents]);
@@ -135,26 +134,9 @@ void SplitterStep::computeFollowupSteps(
   for (unsigned i : indices(components)) {
     unsigned solutionIndex = components[i].solutionIndex;
 
-    // If there are no dependencies, build a normal component step.
-    if (components[i].getDependencies().empty()) {
-      steps.push_back(std::make_unique<ComponentStep>(
-          CS, solutionIndex, &Components[i], std::move(components[i]),
-          PartialSolutions[solutionIndex]));
-      continue;
-    }
-
-    // Note that the partial results from any dependencies of this component
-    // need not be included in the final merged results, because they'll
-    // already be part of the partial results for this component.
-    for (auto dependsOn : components[i].getDependencies()) {
-      IncludeInMergedResults[dependsOn] = false;
-    }
-
-    // Otherwise, build a dependent component "splitter" step, which
-    // handles all combinations of incoming partial solutions.
-    steps.push_back(std::make_unique<DependentComponentSplitterStep>(
-        CS, &Components[i], solutionIndex, std::move(components[i]),
-        llvm::MutableArrayRef(PartialSolutions.get(), numComponents)));
+    steps.push_back(std::make_unique<ComponentStep>(
+        CS, solutionIndex, &Components[i], std::move(components[i]),
+        PartialSolutions[solutionIndex]));
   }
 
   assert(CS.InactiveConstraints.empty() && "Missed a constraint");
@@ -223,8 +205,7 @@ bool SplitterStep::mergePartialSolutions() const {
   SmallVector<unsigned, 2> countsVec;
   countsVec.reserve(numComponents);
   for (unsigned idx : range(numComponents)) {
-    countsVec.push_back(
-        IncludeInMergedResults[idx] ? PartialSolutions[idx].size() : 1);
+    countsVec.push_back(PartialSolutions[idx].size());
   }
 
   // Produce all combinations of partial solutions.
@@ -237,9 +218,6 @@ bool SplitterStep::mergePartialSolutions() const {
     // solutions.
     ConstraintSystem::SolverScope scope(CS);
     for (unsigned i : range(numComponents)) {
-      if (!IncludeInMergedResults[i])
-        continue;
-
       CS.replaySolution(PartialSolutions[i][indices[i]]);
     }
 
@@ -271,87 +249,15 @@ bool SplitterStep::mergePartialSolutions() const {
   return anySolutions;
 }
 
-StepResult DependentComponentSplitterStep::take(bool prevFailed) {
-  // "split" is considered a failure if previous step failed,
-  // or there is a failure recorded by constraint system, or
-  // system can't be simplified.
-  if (prevFailed || CS.getFailedConstraint() || CS.simplify())
-    return done(/*isSuccess=*/false);
-
-  // Figure out the sets of partial solutions that this component depends on.
-  SmallVector<const SmallVector<Solution, 4> *, 2> dependsOnSets;
-  for (auto index : Component.getDependencies()) {
-    dependsOnSets.push_back(&AllPartialSolutions[index]);
-  }
-
-  // Produce all combinations of partial solutions for the inputs.
-  SmallVector<std::unique_ptr<SolverStep>, 4> followup;
-  SmallVector<unsigned, 2> indices(Component.getDependencies().size(), 0);
-  auto dependsOnSetsRef = llvm::ArrayRef(dependsOnSets);
-  do {
-    // Form the set of input partial solutions.
-    SmallVector<const Solution *, 2> dependsOnSolutions;
-    for (auto index : swift::indices(indices)) {
-      dependsOnSolutions.push_back(&(*dependsOnSets[index])[indices[index]]);
-    }
-    ContextualSolutions.push_back(std::make_unique<SmallVector<Solution, 2>>());
-
-    followup.push_back(std::make_unique<ComponentStep>(
-        CS, Index, Constraints, Component, std::move(dependsOnSolutions),
-        *ContextualSolutions.back()));
-  } while (nextCombination(dependsOnSetsRef, indices));
-
-  /// Wait until all of the component steps are done.
-  return suspend(followup);
-}
-
-StepResult DependentComponentSplitterStep::resume(bool prevFailed) {
-  for (auto &ComponentStepSolutions : ContextualSolutions) {
-    Solutions.append(std::make_move_iterator(ComponentStepSolutions->begin()),
-                     std::make_move_iterator(ComponentStepSolutions->end()));
-  }
-  return done(/*isSuccess=*/!Solutions.empty());
-}
-
-void DependentComponentSplitterStep::print(llvm::raw_ostream &Out) {
-  Out << "DependentComponentSplitterStep for dependencies on [";
-  interleave(
-      Component.getDependencies(), [&](unsigned index) { Out << index; },
-      [&] { Out << ", "; });
-  Out << "]\n";
-}
-
 StepResult ComponentStep::take(bool prevFailed) {
   // One of the previous components created by "split"
   // failed, it means that we can't solve this component.
-  if ((prevFailed && DependsOnPartialSolutions.empty()) ||
-      CS.isTooComplex(Solutions) || CS.worseThanBestSolution())
+  if (prevFailed || CS.isTooComplex(Solutions) || CS.worseThanBestSolution())
     return done(/*isSuccess=*/false);
 
   // Setup active scope, only if previous component didn't fail.
   setupScope();
 
-  // If there are any dependent partial solutions to compose, do so now.
-  if (!DependsOnPartialSolutions.empty()) {
-    for (auto partial : DependsOnPartialSolutions) {
-      CS.replaySolution(*partial);
-    }
-
-    // Activate all of the one-way constraints.
-    SmallVector<Constraint *, 4> oneWayConstraints;
-    for (auto &constraint : CS.InactiveConstraints) {
-      if (constraint.isOneWayConstraint())
-        oneWayConstraints.push_back(&constraint);
-    }
-    for (auto constraint : oneWayConstraints) {
-      CS.activateConstraint(constraint);
-    }
-
-    // Simplify again.
-    if (CS.failedConstraint || CS.simplify())
-      return done(/*isSuccess=*/false);
-  }
-
   /// Try to figure out what this step is going to be,
   /// after the scope has been established.
   SmallString<64> potentialBindings;

lib/Sema/CSStep.h

@@ -240,10 +240,6 @@ class SplitterStep final : public SolverStep {
 
   SmallVector<Constraint *, 4> OrphanedConstraints;
 
-  /// Whether to include the partial results of this component in the final
-  /// merged results.
-  SmallVector<bool, 4> IncludeInMergedResults;
-
 public:
   SplitterStep(ConstraintSystem &cs, SmallVectorImpl<Solution> &solutions)
       : SolverStep(cs, solutions) {}
@@ -269,56 +265,6 @@ class SplitterStep final : public SolverStep {
   bool mergePartialSolutions() const;
 };
 
-/// `DependentComponentSplitterStep` is responsible for composing the partial
-/// solutions from other components (on which this component depends) into
-/// the inputs based on which we can solve a particular component.
-class DependentComponentSplitterStep final : public SolverStep {
-  /// Constraints "in scope" of this step.
-  ConstraintList *Constraints;
-
-  /// Index into the parent splitter step.
-  unsigned Index;
-
-  /// The component that has dependencies.
-  ConstraintGraph::Component Component;
-
-  /// Array containing all of the partial solutions for the parent split.
-  MutableArrayRef<SmallVector<Solution, 4>> AllPartialSolutions;
-
-  /// The solutions computed the \c ComponentSteps created for each partial
-  /// solution combinations. Will be merged into the final \c Solutions vector
-  /// in \c resume.
-  std::vector<std::unique_ptr<SmallVector<Solution, 2>>> ContextualSolutions;
-
-  /// Take all of the constraints in this component and put them into
-  /// \c Constraints.
-  void injectConstraints() {
-    for (auto constraint : Component.getConstraints()) {
-      Constraints->erase(constraint);
-      Constraints->push_back(constraint);
-    }
-  }
-
-public:
-  DependentComponentSplitterStep(
-      ConstraintSystem &cs,
-      ConstraintList *constraints,
-      unsigned index,
-      ConstraintGraph::Component &&component,
-      MutableArrayRef<SmallVector<Solution, 4>> allPartialSolutions)
-    : SolverStep(cs, allPartialSolutions[index]), Constraints(constraints),
-      Index(index), Component(std::move(component)),
-      AllPartialSolutions(allPartialSolutions) {
-    assert(!Component.getDependencies().empty() && "Should use ComponentStep");
-    injectConstraints();
-  }
-
-  StepResult take(bool prevFailed) override;
-  StepResult resume(bool prevFailed) override;
-
-  void print(llvm::raw_ostream &Out) override;
-};
-
 
 /// `ComponentStep` represents a set of type variables and related
 /// constraints which could be solved independently. It's further
@@ -381,10 +327,6 @@ class ComponentStep final : public SolverStep {
   /// Constraints "in scope" of this step.
   ConstraintList *Constraints;
 
-  /// The set of partial solutions that should be composed before evaluating
-  /// this component.
-  SmallVector<const Solution *, 2> DependsOnPartialSolutions;
-
   /// Constraint which doesn't have any free type variables associated
   /// with it, which makes it disconnected in the graph.
   Constraint *OrphanedConstraint = nullptr;
@@ -419,8 +361,6 @@ class ComponentStep final : public SolverStep {
       constraints->erase(constraint);
       Constraints->push_back(constraint);
     }
-
-    assert(component.getDependencies().empty());
   }
 
   /// Create a component step that composes existing partial solutions before
@@ -429,15 +369,11 @@ class ComponentStep final : public SolverStep {
       ConstraintSystem &cs, unsigned index,
       ConstraintList *constraints,
       const ConstraintGraph::Component &component,
-      llvm::SmallVectorImpl<const Solution *> &&dependsOnPartialSolutions,
       SmallVectorImpl<Solution> &solutions)
         : SolverStep(cs, solutions), Index(index), IsSingle(false),
           OriginalScore(getCurrentScore()), OriginalBestScore(getBestScore()),
-          Constraints(constraints),
-          DependsOnPartialSolutions(std::move(dependsOnPartialSolutions)) {
+          Constraints(constraints) {
     TypeVars = component.typeVars;
-    assert(DependsOnPartialSolutions.size() ==
-           component.getDependencies().size());
 
     for (auto constraint : component.getConstraints()) {
       constraints->erase(constraint);