[Constraint solver] Handle disjunctions as separate connected components

lib/Sema/CSSolver.cpp

@@ -2089,6 +2089,15 @@ bool ConstraintSystem::solveRec(SmallVectorImpl<Solution> &solutions,
       constraintComponent[constraint] = components[i];
   }
 
+  // Add the orphaned components to the mapping from constraints to components.
+  unsigned firstOrphanedConstraint =
+    numComponents - CG.getOrphanedConstraints().size();
+  {
+    unsigned component = firstOrphanedConstraint;
+    for (auto constraint : CG.getOrphanedConstraints())
+      constraintComponent[constraint] = component++;
+  }
+
   // Sort the constraints into buckets based on component number.
   std::unique_ptr<ConstraintList[]> constraintBuckets(
                                       new ConstraintList[numComponents]);
@@ -2098,6 +2107,9 @@ bool ConstraintSystem::solveRec(SmallVectorImpl<Solution> &solutions,
     constraintBuckets[constraintComponent[constraint]].push_back(constraint);
   }
 
+  // Remove all of the orphaned constraints; we'll introduce them as needed.
+  auto allOrphanedConstraints = CG.takeOrphanedConstraints();
+
   // Function object that returns all constraints placed into buckets
   // back to the list of constraints.
   auto returnAllConstraints = [&] {
@@ -2106,6 +2118,7 @@ bool ConstraintSystem::solveRec(SmallVectorImpl<Solution> &solutions,
       InactiveConstraints.splice(InactiveConstraints.end(), 
                                  constraintBuckets[component]);
     }
+    CG.setOrphanedConstraints(std::move(allOrphanedConstraints));
   };
 
   // Compute the partial solutions produced for each connected component.
@@ -2118,24 +2131,31 @@ bool ConstraintSystem::solveRec(SmallVectorImpl<Solution> &solutions,
     ++solverState->NumComponentsSplit;
 
     // Collect the constraints for this component.
-    InactiveConstraints.splice(InactiveConstraints.end(), 
+    InactiveConstraints.splice(InactiveConstraints.end(),
                                constraintBuckets[component]);
 
-    // Collect the type variables that are not part of a different
-    // component; this includes type variables that are part of the
-    // component as well as already-resolved type variables.
-    // FIXME: The latter could be avoided if we had already
-    // substituted all of those other type variables through.
-    llvm::SmallVector<TypeVariableType *, 16> allTypeVariables 
+    llvm::SmallVector<TypeVariableType *, 16> allTypeVariables
       = std::move(TypeVariables);
-    for (auto typeVar : allTypeVariables) {
-      auto known = typeVarComponent.find(typeVar);
-      if (known != typeVarComponent.end() && known->second != component)
-        continue;
 
-      TypeVariables.push_back(typeVar);
+    Constraint *orphaned = nullptr;
+    if (component < firstOrphanedConstraint) {
+      // Collect the type variables that are not part of a different
+      // component; this includes type variables that are part of the
+      // component as well as already-resolved type variables.
+      for (auto typeVar : allTypeVariables) {
+        auto known = typeVarComponent.find(typeVar);
+        if (known != typeVarComponent.end() && known->second != component)
+          continue;
+
+        TypeVariables.push_back(typeVar);
+      }
+    } else {
+      // Get the orphaned constraint.
+      assert(InactiveConstraints.size() == 1 && "supposed to be an orphan!");
+      orphaned = &InactiveConstraints.front();
     }
-
+    CG.setOrphanedConstraint(orphaned);
+
     // Solve for this component. If it fails, we're done.
     bool failed;
     if (TC.getLangOpts().DebugConstraintSolver) {

lib/Sema/ConstraintGraph.cpp

@@ -349,6 +349,12 @@ void ConstraintGraph::addConstraint(Constraint *constraint) {
     }
   }
 
+  // If the constraint doesn't reference any type variables, it's orphaned;
+  // track it as such.
+  if (referencedTypeVars.empty()) {
+    OrphanedConstraints.push_back(constraint);
+  }
+
   // Record the change, if there are active scopes.
   if (ActiveScope)
     Changes.push_back(Change::addedConstraint(constraint));
@@ -375,6 +381,16 @@ void ConstraintGraph::removeConstraint(Constraint *constraint) {
     }
   }
 
+  // If this is an orphaned constraint, remove it from the list.
+  if (referencedTypeVars.empty()) {
+    auto known = std::find(OrphanedConstraints.begin(),
+                           OrphanedConstraints.end(),
+                           constraint);
+    assert(known != OrphanedConstraints.end() && "missing orphaned constraint");
+    *known = OrphanedConstraints.back();
+    OrphanedConstraints.pop_back();
+  }
+
   // Record the change, if there are active scopes.
   if (ActiveScope)
     Changes.push_back(Change::removedConstraint(constraint));
@@ -578,9 +594,9 @@ unsigned ConstraintGraph::computeConnectedComponents(
     if (CS.getFixedType(TypeVariables[i]))
       continue;
 
-    // If we only care about a subset, and this type variable isn't in that
-    // subset, skip it.
-    if (!typeVarSubset.empty() && typeVarSubset.count(TypeVariables[i]) == 0)
+    // If this type variable isn't in the subset of type variables we care
+    // about, skip it.
+    if (typeVarSubset.count(TypeVariables[i]) == 0)
       continue;
 
     componentHasUnboundTypeVar[components[i]] = true;
@@ -611,7 +627,7 @@ unsigned ConstraintGraph::computeConnectedComponents(
   }
   components.erase(components.begin() + outIndex, components.end());
 
-  return numComponents;
+  return numComponents + getOrphanedConstraints().size();
 }
 
 
@@ -861,6 +877,7 @@ void ConstraintGraph::dump() {
 
 void ConstraintGraph::printConnectedComponents(llvm::raw_ostream &out) {
   SmallVector<TypeVariableType *, 16> typeVars;
+  typeVars.append(TypeVariables.begin(), TypeVariables.end());
   SmallVector<unsigned, 16> components;
   unsigned numComponents = computeConnectedComponents(typeVars, components);
   for (unsigned component = 0; component != numComponents; ++component) {

lib/Sema/ConstraintGraph.h

@@ -237,18 +237,47 @@ class ConstraintGraph {
 
   /// Compute the connected components of the graph.
   ///
-  /// \param typeVars The type variables that occur within the
-  /// connected components. If a non-empty vector is passed in, the algorithm
-  /// will only consider type variables reachable from the initial set.
+  /// \param typeVars The type variables that should be included in the
+  /// set of connected components that are returned.
   ///
   /// \param components Receives the component numbers for each type variable
   /// in \c typeVars.
   ///
-  /// \returns the number of connected components in the graph.
+  /// \returns the number of connected components in the graph, which includes
+  /// one component for each of the constraints produced by
+  /// \c getOrphanedConstraints().
   unsigned computeConnectedComponents(
              SmallVectorImpl<TypeVariableType *> &typeVars,
              SmallVectorImpl<unsigned> &components);
 
+  /// Retrieve the set of "orphaned" constraints, which are known to the
+  /// constraint graph but have no type variables to anchor them.
+  ArrayRef<Constraint *> getOrphanedConstraints() const {
+    return OrphanedConstraints;
+  }
+
+  /// Replace the orphaned constraints with the constraints in the given list,
+  /// returning the old set of orphaned constraints.
+  SmallVector<Constraint *, 4> takeOrphanedConstraints() {
+    auto result = std::move(OrphanedConstraints);
+    OrphanedConstraints.clear();
+    return result;
+  }
+
+  /// Set the orphaned constraints.
+  void setOrphanedConstraints(SmallVector<Constraint *, 4> &&newConstraints) {
+    OrphanedConstraints = std::move(newConstraints);
+  }
+
+  /// Set the list of orphaned constraints to a single constraint.
+  ///
+  /// If \c orphaned is null, just clear out the list.
+  void setOrphanedConstraint(Constraint *orphaned) {
+    OrphanedConstraints.clear();
+    if (orphaned)
+      OrphanedConstraints.push_back(orphaned);
+  }
+
   /// Print the graph.
   void print(llvm::raw_ostream &out);
 
@@ -300,6 +329,9 @@ class ConstraintGraph {
   /// The type variables in this graph, in stable order.
   SmallVector<TypeVariableType *, 4> TypeVariables;
 
+  /// Constraints that are "orphaned" because they contain no type variables.
+  SmallVector<Constraint *, 4> OrphanedConstraints;
+
   /// The kind of change made to the graph.
   enum class ChangeKind {
     /// Added a type variable.

validation-test/Sema/explicit_coercions.swift

@@ -0,0 +1,19 @@
+// RUN: %target-swift-frontend -typecheck %s
+
+public class Foo : CustomReflectable  {
+  public var booleanValue : Bool?
+  public var customMirror: Mirror {
+    return Mirror(self, children: [
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any,
+        "booleanValue": booleanValue as Bool? as Any
+      ])
+  }
+}