Sema: Micro-optimize PotentialBindings

PotentialBindings is part of ConstraintGraphNode and there's no need
to store the ConstraintSystem and TypeVariableType twice.

Also it doesn't need to be optional either, because we no longer need
to reset and recompute bindings.

Author: slavapestov

include/swift/Sema/CSBindings.h

@@ -218,11 +218,6 @@ struct LiteralRequirement {
 };
 
 struct PotentialBindings {
-  /// The constraint system this type variable and its bindings belong to.
-  ConstraintSystem &CS;
-
-  TypeVariableType *TypeVar;
-
   /// The set of all constraints that have been added via infer().
   llvm::SmallPtrSet<Constraint *, 2> Constraints;
 
@@ -265,18 +260,13 @@ struct PotentialBindings {
   llvm::SmallSetVector<std::pair<TypeVariableType *, Constraint *>, 4> SupertypeOf;
   llvm::SmallSetVector<std::pair<TypeVariableType *, Constraint *>, 4> EquivalentTo;
 
-  PotentialBindings(ConstraintSystem &cs, TypeVariableType *typeVar)
-      : CS(cs), TypeVar(typeVar) {}
-
   void addDefault(Constraint *constraint);
 
   void addLiteral(Constraint *constraint);
 
   /// Add a potential binding to the list of bindings,
   /// coalescing supertype bounds when we are able to compute the meet.
-  void addPotentialBinding(PotentialBinding binding);
-
-  bool isGenericParameter() const;
+  void addPotentialBinding(TypeVariableType *typeVar, PotentialBinding binding);
 
   bool isSubtypeOf(TypeVariableType *typeVar) const {
     return llvm::any_of(
@@ -291,17 +281,26 @@ struct PotentialBindings {
   /// Attempt to infer a new binding and other useful information
   /// (i.e. whether bindings should be delayed) from the given
   /// relational constraint.
-  std::optional<PotentialBinding> inferFromRelational(Constraint *constraint);
+  std::optional<PotentialBinding> inferFromRelational(
+      ConstraintSystem &CS,
+      TypeVariableType *TypeVar,
+      Constraint *constraint);
 
 public:
-  void infer(Constraint *constraint);
+  void infer(ConstraintSystem &CS,
+             TypeVariableType *TypeVar,
+             Constraint *constraint);
 
   /// Retract all bindings and other information related to a given
   /// constraint from this binding set.
   ///
   /// This would happen when constraint is simplified or solver backtracks
   /// (either from overload choice or (some) type variable binding).
-  void retract(Constraint *constraint);
+  void retract(ConstraintSystem &CS,
+               TypeVariableType *TypeVar,
+               Constraint *constraint);
+
+  void reset();
 };
 
 
@@ -388,8 +387,9 @@ class BindingSet {
   /// subtype/conversion/equivalence relations with other type variables.
   std::optional<llvm::SmallPtrSet<Constraint *, 4>> TransitiveProtocols;
 
-  BindingSet(const PotentialBindings &info)
-      : CS(info.CS), TypeVar(info.TypeVar), Info(info) {
+  BindingSet(ConstraintSystem &CS, TypeVariableType *TypeVar,
+             const PotentialBindings &info)
+      : CS(CS), TypeVar(TypeVar), Info(info) {
     for (const auto &binding : info.Bindings)
       addBinding(binding, /*isTransitive=*/false);
 
@@ -405,7 +405,7 @@ class BindingSet {
 
   ConstraintSystem &getConstraintSystem() const { return CS; }
 
-  TypeVariableType *getTypeVariable() const { return Info.TypeVar; }
+  TypeVariableType *getTypeVariable() const { return TypeVar; }
 
   /// Check whether this binding set belongs to a type variable
   /// that represents a result type of a closure.

include/swift/Sema/ConstraintGraph.h

@@ -84,7 +84,10 @@ class ConstraintGraphNode {
   /// as this type variable.
   ArrayRef<TypeVariableType *> getEquivalenceClass() const;
 
-  inference::PotentialBindings &getCurrentBindings();
+  inference::PotentialBindings &getCurrentBindings() {
+    assert(forRepresentativeVar());
+    return Bindings;
+  }
 
 private:
   /// Determines whether the type variable associated with this node
@@ -180,7 +183,7 @@ class ConstraintGraphNode {
   TypeVariableType *TypeVar;
 
   /// The set of bindings associated with this type variable.
-  std::optional<inference::PotentialBindings> Bindings;
+  inference::PotentialBindings Bindings;
 
   /// The vector of constraints that mention this type variable, in a stable
   /// order for iteration.

include/swift/Sema/ConstraintSystem.h

@@ -30,7 +30,6 @@
 #include "swift/Basic/Debug.h"
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/OptionSet.h"
-#include "swift/Sema/CSBindings.h"
 #include "swift/Sema/CSFix.h"
 #include "swift/Sema/CSTrail.h"
 #include "swift/Sema/Constraint.h"

lib/Sema/CSBindings.cpp

@@ -35,11 +35,11 @@ static std::optional<Type> checkTypeOfBinding(TypeVariableType *typeVar,
                                               Type type);
 
 bool BindingSet::forClosureResult() const {
-  return Info.TypeVar->getImpl().isClosureResultType();
+  return TypeVar->getImpl().isClosureResultType();
 }
 
 bool BindingSet::forGenericParameter() const {
-  return bool(Info.TypeVar->getImpl().getGenericParameter());
+  return bool(TypeVar->getImpl().getGenericParameter());
 }
 
 bool BindingSet::canBeNil() const {
@@ -54,10 +54,10 @@ bool BindingSet::isDirectHole() const {
     return false;
 
   return Bindings.empty() && getNumViableLiteralBindings() == 0 &&
-         Defaults.empty() && Info.TypeVar->getImpl().canBindToHole();
+         Defaults.empty() && TypeVar->getImpl().canBindToHole();
 }
 
-bool PotentialBindings::isGenericParameter() const {
+static bool isGenericParameter(TypeVariableType *TypeVar) {
   auto *locator = TypeVar->getImpl().getLocator();
   return locator && locator->isLastElement<LocatorPathElt::GenericParameter>();
 }
@@ -178,7 +178,7 @@ bool BindingSet::involvesTypeVariables() const {
 
 bool BindingSet::isPotentiallyIncomplete() const {
   // Generic parameters are always potentially incomplete.
-  if (Info.isGenericParameter())
+  if (isGenericParameter(TypeVar))
     return true;
 
   // Key path literal type is incomplete until there is a
@@ -1168,7 +1168,8 @@ LiteralRequirement::isCoveredBy(const PotentialBinding &binding, bool canBeNil,
   } while (true);
 }
 
-void PotentialBindings::addPotentialBinding(PotentialBinding binding) {
+void PotentialBindings::addPotentialBinding(TypeVariableType *TypeVar,
+                                            PotentialBinding binding) {
   assert(!binding.BindingType->is<ErrorType>());
 
   // If the type variable can't bind to an lvalue, make sure the
@@ -1430,7 +1431,7 @@ BindingSet ConstraintSystem::getBindingsFor(TypeVariableType *typeVar,
          "not a representative");
   assert(!typeVar->getImpl().getFixedType(nullptr) && "has a fixed type");
 
-  BindingSet bindings{CG[typeVar].getCurrentBindings()};
+  BindingSet bindings(*this, typeVar, CG[typeVar].getCurrentBindings());
 
   if (finalize) {
     llvm::SmallDenseMap<TypeVariableType *, BindingSet> cache;
@@ -1473,7 +1474,9 @@ static std::optional<Type> checkTypeOfBinding(TypeVariableType *typeVar,
 }
 
 std::optional<PotentialBinding>
-PotentialBindings::inferFromRelational(Constraint *constraint) {
+PotentialBindings::inferFromRelational(ConstraintSystem &CS,
+                                       TypeVariableType *TypeVar,
+                                       Constraint *constraint) {
   assert(constraint->getClassification() ==
              ConstraintClassification::Relational &&
          "only relational constraints handled here");
@@ -1669,7 +1672,7 @@ PotentialBindings::inferFromRelational(Constraint *constraint) {
     // Since inference now happens during constraint generation,
     // this hack should be allowed in both `Solving`
     // (during non-diagnostic mode) and `ConstraintGeneration` phases.
-    if (isGenericParameter() &&
+    if (isGenericParameter(TypeVar) &&
         (!CS.shouldAttemptFixes() ||
          CS.getPhase() == ConstraintSystemPhase::ConstraintGeneration)) {
       type = fnTy->withExtInfo(fnTy->getExtInfo().withNoEscape(false));
@@ -1778,7 +1781,9 @@ PotentialBindings::inferFromRelational(Constraint *constraint) {
 /// Retrieve the set of potential type bindings for the given
 /// representative type variable, along with flags indicating whether
 /// those types should be opened.
-void PotentialBindings::infer(Constraint *constraint) {
+void PotentialBindings::infer(ConstraintSystem &CS,
+                              TypeVariableType *TypeVar,
+                              Constraint *constraint) {
   if (!Constraints.insert(constraint).second)
     return;
 
@@ -1799,11 +1804,11 @@ void PotentialBindings::infer(Constraint *constraint) {
   case ConstraintKind::OptionalObject:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::LValueObject: {
-    auto binding = inferFromRelational(constraint);
+    auto binding = inferFromRelational(CS, TypeVar, constraint);
     if (!binding)
       break;
 
-    addPotentialBinding(*binding);
+    addPotentialBinding(TypeVar, *binding);
     break;
   }
   case ConstraintKind::KeyPathApplication: {
@@ -1952,7 +1957,9 @@ void PotentialBindings::infer(Constraint *constraint) {
   }
 }
 
-void PotentialBindings::retract(Constraint *constraint) {
+void PotentialBindings::retract(ConstraintSystem &CS,
+                                TypeVariableType *TypeVar,
+                                Constraint *constraint) {
   if (!Constraints.erase(constraint))
     return;
 
@@ -2023,6 +2030,20 @@ void PotentialBindings::retract(Constraint *constraint) {
   EquivalentTo.remove_if(hasMatchingSource);
 }
 
+void PotentialBindings::reset() {
+  Constraints.clear();
+  Bindings.clear();
+  Protocols.clear();
+  Literals.clear();
+  Defaults.clear();
+  DelayedBy.clear();
+  AdjacentVars.clear();
+  AssociatedCodeCompletionToken = ASTNode();
+  SubtypeOf.clear();
+  SupertypeOf.clear();
+  EquivalentTo.clear();
+}
+
 void BindingSet::forEachLiteralRequirement(
     llvm::function_ref<void(KnownProtocolKind)> callback) const {
   for (const auto &literal : Literals) {

lib/Sema/ConstraintGraph.cpp

@@ -289,19 +289,11 @@ void ConstraintGraphNode::removeReferencedBy(TypeVariableType *typeVar) {
   }
 }
 
-inference::PotentialBindings &ConstraintGraphNode::getCurrentBindings() {
-  assert(forRepresentativeVar());
-
-  if (!Bindings)
-    Bindings.emplace(CG.getConstraintSystem(), TypeVar);
-  return *Bindings;
-}
-
 void ConstraintGraphNode::introduceToInference(Constraint *constraint) {
   if (forRepresentativeVar()) {
     auto fixedType = TypeVar->getImpl().getFixedType(/*record=*/nullptr);
     if (!fixedType)
-      getCurrentBindings().infer(constraint);
+      getCurrentBindings().infer(CG.getConstraintSystem(), TypeVar, constraint);
   } else {
     auto *repr =
         getTypeVariable()->getImpl().getRepresentative(/*record=*/nullptr);
@@ -313,7 +305,7 @@ void ConstraintGraphNode::retractFromInference(Constraint *constraint) {
   if (forRepresentativeVar()) {
     auto fixedType = TypeVar->getImpl().getFixedType(/*record=*/nullptr);
     if (!fixedType)
-      getCurrentBindings().retract(constraint);
+      getCurrentBindings().retract(CG.getConstraintSystem(), TypeVar,constraint);
   } else {
     auto *repr =
         getTypeVariable()->getImpl().getRepresentative(/*record=*/nullptr);
@@ -577,12 +569,12 @@ void ConstraintGraph::unrelateTypeVariables(TypeVariableType *typeVar,
 
 void ConstraintGraph::inferBindings(TypeVariableType *typeVar,
                                     Constraint *constraint) {
-  (*this)[typeVar].getCurrentBindings().infer(constraint);
+  (*this)[typeVar].getCurrentBindings().infer(CS, typeVar, constraint);
 }
 
 void ConstraintGraph::retractBindings(TypeVariableType *typeVar,
                                       Constraint *constraint) {
-  (*this)[typeVar].getCurrentBindings().retract(constraint);
+  (*this)[typeVar].getCurrentBindings().retract(CS, typeVar, constraint);
 }
 
 #pragma mark Algorithms