Sema: Special-case recording of Bind constraint in PreparedOverload

Author: slavapestov

include/swift/Sema/PreparedOverload.h

@@ -71,6 +71,9 @@ struct PreparedOverloadChange {
     /// A generic requirement was opened to a constraint.
     AddedConstraint,
 
+    /// Special case of a Bind constraint.
+    AddedBindConstraint,
+
     /// A mapping of generic parameter types to type variables
     /// was recorded.
     OpenedTypes,
@@ -98,6 +101,11 @@ struct PreparedOverloadChange {
     /// For ChangeKind::AddedConstraint.
     Constraint *TheConstraint;
 
+    struct {
+      TypeBase *FirstType;
+      TypeBase * SecondType;
+    } Bind;
+
     /// For ChangeKind::OpenedTypes.
     struct {
       const OpenedType *Data;
@@ -192,6 +200,14 @@ struct PreparedOverloadBuilder {
     Changes.push_back(change);
   }
 
+  void addedBindConstraint(Type firstType, Type secondType) {
+    PreparedOverload::Change change;
+    change.Kind = PreparedOverload::Change::AddedBindConstraint;
+    change.Bind.FirstType = firstType.getPointer();
+    change.Bind.SecondType = secondType.getPointer();
+    Changes.push_back(change);
+  }
+
   void openedTypes(ArrayRef<OpenedType> replacements) {
     PreparedOverload::Change change;
     change.Kind = PreparedOverload::Change::OpenedTypes;

lib/Sema/CSSimplify.cpp

@@ -16365,6 +16365,11 @@ void ConstraintSystem::addConstraint(ConstraintKind kind, Type first,
                                      PreparedOverloadBuilder *preparedOverload) {
   if (preparedOverload) {
     ASSERT(PreparingOverload);
+    if (kind == ConstraintKind::Bind) {
+      ASSERT(!isFavored);
+      preparedOverload->addedBindConstraint(first, second);
+      return;
+    }
     auto c = Constraint::create(*this, kind, first, second,
                                 getConstraintLocator(locator));
     if (isFavored) c->setFavored();

lib/Sema/TypeOfReference.cpp

@@ -2510,6 +2510,13 @@ void ConstraintSystem::replayChanges(
       simplifyDisjunctionChoice(change.TheConstraint);
       break;
 
+    case PreparedOverload::Change::AddedBindConstraint:
+      addConstraint(ConstraintKind::Bind,
+                    change.Bind.FirstType,
+                    change.Bind.SecondType,
+                    locator, /*isFavored=*/false);
+      break;
+
     case PreparedOverload::Change::OpenedTypes: {
       ArrayRef<OpenedType> replacements(
           change.Replacements.Data,