[ConstraintSystem] Add cache for conformance lookups

`lookupConformance` request is not cached and constraint solver
performs a lot of them for the same type (i.e. during disjunction
solving), let's try to cache previously performed requests to
see whether additional memory use is worth the performance benefit.

Author: xedin

include/swift/Sema/CSBindings.h

@@ -195,23 +195,22 @@ struct LiteralRequirement {
   /// \param canBeNil The flag that determines whether given type
   /// variable requires all of its bindings to be optional.
   ///
-  /// \param useDC The declaration context in which this literal
-  /// requirement is used.
+  /// \param CS The constraint system this literal requirement belongs to.
   ///
   /// \returns a pair of bool and a type:
   ///    - bool, true if binding covers given literal protocol;
   ///    - type, non-null if binding type has to be adjusted
   ///      to cover given literal protocol;
   std::pair<bool, Type> isCoveredBy(const PotentialBinding &binding,
                                     bool canBeNil,
-                                    DeclContext *useDC) const;
+                                    ConstraintSystem &CS) const;
 
   /// Determines whether literal protocol associated with this
   /// meta-information is viable for inclusion as a defaultable binding.
   bool viableAsBinding() const { return !isCovered() && hasDefaultType(); }
 
 private:
-  bool isCoveredBy(Type type, DeclContext *useDC) const;
+  bool isCoveredBy(Type type, ConstraintSystem &CS) const;
 };
 
 struct PotentialBindings {

include/swift/Sema/ConstraintSystem.h

@@ -2250,6 +2250,10 @@ class ConstraintSystem {
   llvm::SmallMapVector<ConstraintLocator *, ArrayRef<OpenedType>, 4>
       OpenedTypes;
 
+  /// A dictionary of all conformances that have been looked up by the solver.
+  llvm::DenseMap<std::pair<TypeBase *, ProtocolDecl *>, ProtocolConformanceRef>
+      Conformances;
+
   /// The list of all generic requirements fixed along the current
   /// solver path.
   using FixedRequirement =
@@ -3946,7 +3950,7 @@ class ConstraintSystem {
   ///
   /// \param wantRValue Whether this routine should look through
   /// lvalues at each step.
-  Type getFixedTypeRecursive(Type type, bool wantRValue) const {
+  Type getFixedTypeRecursive(Type type, bool wantRValue) {
     TypeMatchOptions flags = llvm::None;
     return getFixedTypeRecursive(type, flags, wantRValue);
   }
@@ -3964,7 +3968,7 @@ class ConstraintSystem {
   /// \param wantRValue Whether this routine should look through
   /// lvalues at each step.
   Type getFixedTypeRecursive(Type type, TypeMatchOptions &flags,
-                             bool wantRValue) const;
+                             bool wantRValue);
 
   /// Determine whether the given type variable occurs within the given type.
   ///
@@ -4198,6 +4202,10 @@ class ConstraintSystem {
          ConstraintLocatorBuilder locator,
          const OpenedTypeMap &replacements);
 
+  /// Check whether the given type conforms to the given protocol and if
+  /// so return a valid conformance reference.
+  ProtocolConformanceRef lookupConformance(Type type, ProtocolDecl *P);
+
   /// Wrapper over swift::adjustFunctionTypeForConcurrency that passes along
   /// the appropriate closure-type and opening extraction functions.
   AnyFunctionType *adjustFunctionTypeForConcurrency(
@@ -4711,7 +4719,7 @@ class ConstraintSystem {
   ///
   /// The resulting types can be compared canonically, so long as additional
   /// type equivalence requirements aren't introduced between comparisons.
-  Type simplifyType(Type type) const;
+  Type simplifyType(Type type);
 
   /// Simplify a type, by replacing type variables with either their
   /// fixed types (if available) or their representatives.
@@ -4791,8 +4799,9 @@ class ConstraintSystem {
 
   /// Simplifies a type by replacing type variables with the result of
   /// \c getFixedTypeFn and performing lookup on dependent member types.
-  Type simplifyTypeImpl(Type type,
-      llvm::function_ref<Type(TypeVariableType *)> getFixedTypeFn) const;
+  Type
+  simplifyTypeImpl(Type type,
+                   llvm::function_ref<Type(TypeVariableType *)> getFixedTypeFn);
 
   /// Attempt to simplify the given construction constraint.
   ///

lib/Sema/CSBindings.cpp

@@ -669,7 +669,7 @@ void BindingSet::determineLiteralCoverage() {
       Type adjustedTy;
 
       std::tie(isCovered, adjustedTy) =
-          literal.isCoveredBy(*binding, allowsNil, CS.DC);
+          literal.isCoveredBy(*binding, allowsNil, CS);
 
       if (!isCovered)
         continue;
@@ -872,7 +872,7 @@ void PotentialBindings::addDefault(Constraint *constraint) {
   Defaults.insert(constraint);
 }
 
-bool LiteralRequirement::isCoveredBy(Type type, DeclContext *useDC) const {
+bool LiteralRequirement::isCoveredBy(Type type, ConstraintSystem &CS) const {
   auto coversDefaultType = [](Type type, Type defaultType) -> bool {
     if (!defaultType->hasUnboundGenericType())
       return type->isEqual(defaultType);
@@ -892,14 +892,12 @@ bool LiteralRequirement::isCoveredBy(Type type, DeclContext *useDC) const {
   if (hasDefaultType() && coversDefaultType(type, getDefaultType()))
     return true;
 
-  return (bool)TypeChecker::conformsToProtocol(type, getProtocol(),
-                                               useDC->getParentModule());
+  return bool(CS.lookupConformance(type, getProtocol()));
 }
 
 std::pair<bool, Type>
-LiteralRequirement::isCoveredBy(const PotentialBinding &binding,
-                                bool canBeNil,
-                                DeclContext *useDC) const {
+LiteralRequirement::isCoveredBy(const PotentialBinding &binding, bool canBeNil,
+                                ConstraintSystem &CS) const {
   auto type = binding.BindingType;
   switch (binding.Kind) {
   case AllowedBindingKind::Exact:
@@ -919,7 +917,7 @@ LiteralRequirement::isCoveredBy(const PotentialBinding &binding,
     if (type->isTypeVariableOrMember() || type->isPlaceholder())
       return std::make_pair(false, Type());
 
-    if (isCoveredBy(type, useDC)) {
+    if (isCoveredBy(type, CS)) {
       return std::make_pair(true, requiresUnwrap ? type : binding.BindingType);
     }
 

lib/Sema/CSGen.cpp

@@ -425,8 +425,7 @@ namespace {
       // the literal.
       if (otherArgTy && otherArgTy->getAnyNominal()) {
         if (otherArgTy->isEqual(paramTy) &&
-            TypeChecker::conformsToProtocol(
-                otherArgTy, literalProto, CS.DC->getParentModule())) {
+            CS.lookupConformance(otherArgTy, literalProto)) {
           return true;
         }
       } else if (Type defaultType =

lib/Sema/CSSimplify.cpp

@@ -8425,8 +8425,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
     }
 
     // Check whether this type conforms to the protocol.
-    auto conformance = DC->getParentModule()->lookupConformance(
-        type, protocol, /*allowMissing=*/true);
+    auto conformance = lookupConformance(type, protocol);
     if (conformance) {
       return recordConformance(conformance);
     }
@@ -8546,8 +8545,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
 
       if (auto rawValue = isRawRepresentable(*this, type)) {
         if (!rawValue->isTypeVariableOrMember() &&
-            TypeChecker::conformsToProtocol(rawValue, protocol,
-                                            DC->getParentModule())) {
+            lookupConformance(rawValue, protocol)) {
           auto *fix = UseRawValue::create(*this, type, protocolTy, loc);
           // Since this is a conformance requirement failure (where the
           // source is most likely an argument), let's increase its impact
@@ -8706,11 +8704,9 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyTransitivelyConformsTo(
 
   auto *protocol = protocolTy->castTo<ProtocolType>()->getDecl();
 
-  auto *M = DC->getParentModule();
-
   // First, let's check whether the type itself conforms,
   // if it does - we are done.
-  if (M->lookupConformance(resolvedTy, protocol))
+  if (lookupConformance(resolvedTy, protocol))
     return SolutionKind::Solved;
 
   // If the type doesn't conform, let's check whether
@@ -8782,10 +8778,9 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyTransitivelyConformsTo(
     }
   }
 
-  return llvm::any_of(typesToCheck,
-                      [&](Type type) {
-                        return bool(M->lookupConformance(type, protocol));
-                      })
+  return llvm::any_of(
+             typesToCheck,
+             [&](Type type) { return bool(lookupConformance(type, protocol)); })
              ? SolutionKind::Solved
              : SolutionKind::Error;
 }
@@ -9372,7 +9367,7 @@ static bool mayBeForKeyPathSubscriptWithoutLabel(ConstraintSystem &cs,
 /// This is useful to figure out whether it makes sense to
 /// perform dynamic member lookup or not.
 static bool
-allFromConditionalConformances(DeclContext *DC, Type baseTy,
+allFromConditionalConformances(ConstraintSystem &cs, Type baseTy,
                                ArrayRef<OverloadChoice> candidates) {
   auto *NTD = baseTy->getAnyNominal();
   if (!NTD)
@@ -9391,8 +9386,7 @@ allFromConditionalConformances(DeclContext *DC, Type baseTy,
     }
 
     if (auto *protocol = candidateDC->getSelfProtocolDecl()) {
-      auto conformance = DC->getParentModule()->lookupConformance(
-          baseTy, protocol);
+      auto conformance = cs.lookupConformance(baseTy, protocol);
       if (!conformance.isConcrete())
         return false;
 
@@ -10130,7 +10124,7 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
     const auto &candidates = result.ViableCandidates;
 
     if ((candidates.empty() ||
-         allFromConditionalConformances(DC, instanceTy, candidates)) &&
+         allFromConditionalConformances(*this, instanceTy, candidates)) &&
         !isSelfRecursiveKeyPathDynamicMemberLookup(*this, baseTy,
                                                    memberLocator)) {
       auto &ctx = getASTContext();
@@ -10713,7 +10707,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
       // called within extensions to that type (usually adding 'clamp').
       bool treatAsViable =
           (member.isSimpleName("min") || member.isSimpleName("max")) &&
-          allFromConditionalConformances(DC, baseTy, result.ViableCandidates);
+          allFromConditionalConformances(*this, baseTy,
+                                         result.ViableCandidates);
 
       generateConstraints(
           candidates, memberTy, outerAlternatives, useDC, locator, llvm::None,
@@ -11121,8 +11116,7 @@ ConstraintSystem::simplifyValueWitnessConstraint(
   // conformance already?
   auto proto = requirement->getDeclContext()->getSelfProtocolDecl();
   assert(proto && "Value witness constraint for a non-requirement");
-  auto conformance = useDC->getParentModule()->lookupConformance(
-      baseObjectType, proto);
+  auto conformance = lookupConformance(baseObjectType, proto);
   if (!conformance)
     return fail();
 

lib/Sema/CSSolver.cpp

@@ -2175,8 +2175,7 @@ void DisjunctionChoiceProducer::partitionGenericOperators(
     if (auto *refined = dyn_cast<ProtocolDecl>(nominal))
       return refined->inheritsFrom(protocol);
 
-    return (bool)TypeChecker::conformsToProtocol(nominal->getDeclaredType(), protocol,
-                                                 CS.DC->getParentModule());
+    return bool(CS.lookupConformance(nominal->getDeclaredType(), protocol));
   };
 
   // Gather Numeric and Sequence overloads into separate buckets.

lib/Sema/ConstraintSystem.cpp

@@ -1196,9 +1196,8 @@ llvm::Optional<Type> ConstraintSystem::isSetType(Type type) {
   return llvm::None;
 }
 
-Type ConstraintSystem::getFixedTypeRecursive(Type type,
-                                             TypeMatchOptions &flags,
-                                             bool wantRValue) const {
+Type ConstraintSystem::getFixedTypeRecursive(Type type, TypeMatchOptions &flags,
+                                             bool wantRValue) {
 
   if (wantRValue)
     type = type->getRValueType();
@@ -3822,7 +3821,7 @@ void ConstraintSystem::resolveOverload(ConstraintLocator *locator,
 namespace {
 
 struct TypeSimplifier {
-  const ConstraintSystem &CS;
+  ConstraintSystem &CS;
   llvm::function_ref<Type(TypeVariableType *)> GetFixedTypeFn;
 
   struct ActivePackExpansion {
@@ -3831,7 +3830,7 @@ struct TypeSimplifier {
   };
   SmallVector<ActivePackExpansion, 4> ActivePackExpansions;
 
-  TypeSimplifier(const ConstraintSystem &CS,
+  TypeSimplifier(ConstraintSystem &CS,
                  llvm::function_ref<Type(TypeVariableType *)> getFixedTypeFn)
     : CS(CS), GetFixedTypeFn(getFixedTypeFn) {}
 
@@ -3979,8 +3978,7 @@ struct TypeSimplifier {
       if (lookupBaseType->mayHaveMembers() ||
           lookupBaseType->is<PackType>()) {
         auto *proto = assocType->getProtocol();
-        auto conformance = CS.DC->getParentModule()->lookupConformance(
-          lookupBaseType, proto);
+        auto conformance = CS.lookupConformance(lookupBaseType, proto);
         if (!conformance) {
           // If the base type doesn't conform to the associatedtype's protocol,
           // there will be a missing conformance fix applied in diagnostic mode,
@@ -4011,11 +4009,11 @@ struct TypeSimplifier {
 } // end anonymous namespace
 
 Type ConstraintSystem::simplifyTypeImpl(Type type,
-    llvm::function_ref<Type(TypeVariableType *)> getFixedTypeFn) const {
+    llvm::function_ref<Type(TypeVariableType *)> getFixedTypeFn) {
   return type.transform(TypeSimplifier(*this, getFixedTypeFn));
 }
 
-Type ConstraintSystem::simplifyType(Type type) const {
+Type ConstraintSystem::simplifyType(Type type) {
   if (!type->hasTypeVariable())
     return type;
 
@@ -6098,15 +6096,12 @@ bool constraints::hasAppliedSelf(const OverloadChoice &choice,
 /// Check whether given type conforms to `RawRepresentable` protocol
 /// and return the witness type.
 Type constraints::isRawRepresentable(ConstraintSystem &cs, Type type) {
-  auto *DC = cs.DC;
-
   auto rawReprType = TypeChecker::getProtocol(
       cs.getASTContext(), SourceLoc(), KnownProtocolKind::RawRepresentable);
   if (!rawReprType)
     return Type();
 
-  auto conformance = TypeChecker::conformsToProtocol(type, rawReprType,
-                                                     DC->getParentModule());
+  auto conformance = cs.lookupConformance(type, rawReprType);
   if (conformance.isInvalid())
     return Type();
 
@@ -7342,6 +7337,21 @@ bool ConstraintSystem::participatesInInference(ClosureExpr *closure) const {
   return true;
 }
 
+ProtocolConformanceRef
+ConstraintSystem::lookupConformance(Type type, ProtocolDecl *protocol) {
+  auto cacheKey = std::make_pair(type.getPointer(), protocol);
+
+  auto cachedConformance = Conformances.find(cacheKey);
+  if (cachedConformance != Conformances.end())
+    return cachedConformance->second;
+
+  auto conformance =
+      DC->getParentModule()->lookupConformance(type, protocol,
+                                               /*allowMissing=*/true);
+  Conformances[cacheKey] = conformance;
+  return conformance;
+}
+
 TypeVarBindingProducer::TypeVarBindingProducer(BindingSet &bindings)
     : BindingProducer(bindings.getConstraintSystem(),
                       bindings.getTypeVariable()->getImpl().getLocator()),
@@ -7474,7 +7484,7 @@ bool TypeVarBindingProducer::requiresOptionalAdjustment(
     auto *proto = CS.getASTContext().getProtocol(
          KnownProtocolKind::ExpressibleByNilLiteral);
 
-    return !proto->getParentModule()->lookupConformance(type, proto);
+    return !CS.lookupConformance(type, proto);
   } else if (binding.isDefaultableBinding() && binding.BindingType->isAny()) {
     return true;
   }

test/Constraints/array_literal.swift

@@ -358,6 +358,7 @@ protocol P { }
 struct PArray<T> { }
 
 extension PArray : ExpressibleByArrayLiteral where T: P {
+  // expected-note@-1 {{requirement from conditional conformance of 'PArray<String>' to 'ExpressibleByArrayLiteral'}}
   typealias ArrayLiteralElement = T
 
   init(arrayLiteral elements: T...) { }
@@ -367,7 +368,7 @@ extension Int: P { }
 
 func testConditional(i: Int, s: String) {
   let _: PArray<Int> = [i, i, i]
-  let _: PArray<String> = [s, s, s] // expected-error{{cannot convert value of type '[String]' to specified type 'PArray<String>'}}
+  let _: PArray<String> = [s, s, s] // expected-error{{generic struct 'PArray' requires that 'String' conform to 'P'}}
 }