Sema: Split up SolverTrail::Change::BoundTypeVariable

Author: slavapestov

include/swift/Sema/CSTrail.h

@@ -37,16 +37,16 @@ class SolverTrail {
 
   /// The kind of change made to the graph.
   enum class ChangeKind {
-    /// Added a type variable to the constraint graph.
+    /// Added a new vertex to the constraint graph.
     AddedTypeVariable,
     /// Added a new constraint to the constraint graph.
     AddedConstraint,
     /// Removed an existing constraint from the constraint graph.
     RemovedConstraint,
     /// Extended the equivalence class of a type variable in the constraint graph.
     ExtendedEquivalenceClass,
-    /// Added a fixed binding for a type variable in the constraint graph.
-    BoundTypeVariable,
+    /// Added a new edge in the constraint graph.
+    RelatedTypeVariables,
     /// Introduced a type variable's fixed type to inference.
     IntroducedToInference,
     /// Set the fixed type or parent and flags for a type variable.
@@ -74,6 +74,14 @@ class SolverTrail {
         unsigned PrevSize;
       } EquivClass;
 
+      struct {
+        /// The first type variable.
+        TypeVariableType *TypeVar;
+
+        /// The second type variable.
+        TypeVariableType *OtherTypeVar;
+      } Relation;
+
       struct {
         /// The type variable being bound to a fixed type.
         TypeVariableType *TypeVar;
@@ -109,8 +117,10 @@ class SolverTrail {
     static Change extendedEquivalenceClass(TypeVariableType *typeVar,
                                            unsigned prevSize);
 
-    /// Create a change that bound a type variable to a fixed type.
-    static Change boundTypeVariable(TypeVariableType *typeVar, Type fixed);
+    /// Create a change that updated the references/referenced by sets of
+    /// a type variable pair.
+    static Change relatedTypeVariables(TypeVariableType *typeVar,
+                                       TypeVariableType *otherTypeVar);
 
     /// Create a change that introduced a type variable to inference.
     static Change introducedToInference(TypeVariableType *typeVar, Type fixed);

include/swift/Sema/ConstraintGraph.h

@@ -424,11 +424,12 @@ class ConstraintGraph {
   /// caution.
   void removeNode(TypeVariableType *typeVar);
 
-  /// Unbind the given type variable from the given fixed type.
+  /// Remove an edge from the constraint graph.
   ///
   /// Note that this change is not recorded and cannot be undone. Use with
   /// caution.
-  void unbindTypeVariable(TypeVariableType *typeVar, Type fixedType);
+  void unrelateTypeVariables(TypeVariableType *typeVar,
+                             TypeVariableType *otherTypeVar);
 
   /// Retract the given type variable from inference.
   ///

lib/Sema/CSTrail.cpp

@@ -76,12 +76,12 @@ SolverTrail::Change::extendedEquivalenceClass(TypeVariableType *typeVar,
 }
 
 SolverTrail::Change
-SolverTrail::Change::boundTypeVariable(TypeVariableType *typeVar,
-                                       Type fixed) {
+SolverTrail::Change::relatedTypeVariables(TypeVariableType *typeVar,
+                                          TypeVariableType *otherTypeVar) {
   Change result;
-  result.Kind = ChangeKind::BoundTypeVariable;
-  result.Binding.TypeVar = typeVar;
-  result.Binding.FixedType = fixed.getPointer();
+  result.Kind = ChangeKind::RelatedTypeVariables;
+  result.Relation.TypeVar = typeVar;
+  result.Relation.OtherTypeVar = otherTypeVar;
   return result;
 }
 
@@ -130,8 +130,8 @@ void SolverTrail::Change::undo(ConstraintSystem &cs) const {
     break;
    }
 
-  case ChangeKind::BoundTypeVariable:
-    cg.unbindTypeVariable(Binding.TypeVar, Binding.FixedType);
+  case ChangeKind::RelatedTypeVariables:
+    cg.unrelateTypeVariables(Relation.TypeVar, Relation.OtherTypeVar);
     break;
 
   case ChangeKind::IntroducedToInference:
@@ -179,11 +179,11 @@ void SolverTrail::Change::dump(llvm::raw_ostream &out,
     break;
    }
 
-  case ChangeKind::BoundTypeVariable:
-    out << "(bound type variable ";
-    Binding.TypeVar->print(out, PO);
-    out << " to fixed type ";
-    Binding.FixedType->print(out, PO);
+  case ChangeKind::RelatedTypeVariables:
+    out << "(related type variable ";
+    Relation.TypeVar->print(out, PO);
+    out << " with ";
+    Relation.OtherTypeVar->print(out, PO);
     out << ")\n";
     break;
 

lib/Sema/ConstraintGraph.cpp

@@ -559,29 +559,24 @@ void ConstraintGraph::bindTypeVariable(TypeVariableType *typeVar, Type fixed) {
 
     otherNode.addReferencedBy(typeVar);
     node.addReferencedVar(otherTypeVar);
-  }
 
-  // Record the change, if there are active scopes.
-  if (CS.isRecordingChanges())
-    CS.recordChange(SolverTrail::Change::boundTypeVariable(typeVar, fixed));
+    // Record the change, if there are active scopes.
+    if (CS.isRecordingChanges())
+      CS.recordChange(SolverTrail::Change::relatedTypeVariables(typeVar, otherTypeVar));
+  }
 }
 
 void ConstraintGraph::introduceToInference(TypeVariableType *typeVar, Type fixed) {
   (*this)[typeVar].introduceToInference(fixed);
 }
 
-void ConstraintGraph::unbindTypeVariable(TypeVariableType *typeVar, Type fixed) {
+void ConstraintGraph::unrelateTypeVariables(TypeVariableType *typeVar,
+                                            TypeVariableType *otherTypeVar) {
   auto &node = (*this)[typeVar];
+  auto &otherNode = (*this)[otherTypeVar];
 
-  llvm::SmallPtrSet<TypeVariableType *, 4> referencedVars;
-  fixed->getTypeVariables(referencedVars);
-
-  for (auto otherTypeVar : referencedVars) {
-    auto &otherNode = (*this)[otherTypeVar];
-
-    otherNode.removeReferencedBy(typeVar);
-    node.removeReference(otherTypeVar);
-  }
+  otherNode.removeReferencedBy(typeVar);
+  node.removeReference(otherTypeVar);
 }
 
 void ConstraintGraph::retractFromInference(TypeVariableType *typeVar, Type fixed) {