[GSB] Delete all of the "visited" sets, which are now unused.

Now that we detect recursion based on repetition within the potential
archetypes, we no longer rely on passing down "visited" sets to
detect/diagnose recursion. Remove them.

Author: DougGregor

include/swift/AST/GenericSignatureBuilder.h

@@ -267,12 +267,6 @@ class GenericSignatureBuilder {
                                              ProtocolDecl *Proto,
                                              const RequirementSource *Source);
 
-  ConstraintResult addConformanceRequirement(
-                               PotentialArchetype *T,
-                               ProtocolDecl *Proto,
-                               const RequirementSource *Source,
-                               llvm::SmallPtrSetImpl<ProtocolDecl *> &Visited);
-
 public:
   /// \brief Add a new same-type requirement between two fully resolved types
   /// (output of \c GenericSignatureBuilder::resolve).
@@ -338,9 +332,7 @@ class GenericSignatureBuilder {
                           UnresolvedType subject,
                           UnresolvedType constraint,
                           FloatingRequirementSource source,
-                          UnresolvedHandlingKind unresolvedHandling,
-                          llvm::SmallPtrSetImpl<ProtocolDecl *> *visited
-                            = nullptr);
+                          UnresolvedHandlingKind unresolvedHandling);
 
   /// \brief Add a new conformance requirement specifying that the given
   /// potential archetypes are equivalent.
@@ -388,7 +380,6 @@ class GenericSignatureBuilder {
                                 TypeDecl *decl,
                                 UnresolvedType type,
                                 const RequirementSource *parentSource,
-                                llvm::SmallPtrSetImpl<ProtocolDecl *> &visited,
                                 ModuleDecl *inferForModule);
 
   /// Visit all of the potential archetypes.
@@ -480,13 +471,6 @@ class GenericSignatureBuilder {
                                   ModuleDecl *inferForModule,
                                   const SubstitutionMap *subMap = nullptr);
 
-  ConstraintResult addRequirement(
-                                const Requirement &req,
-                                FloatingRequirementSource source,
-                                ModuleDecl *inferForModule,
-                                const SubstitutionMap *subMap,
-                                llvm::SmallPtrSetImpl<ProtocolDecl *> &Visited);
-
   /// \brief Add all of a generic signature's parameters and requirements.
   void addGenericSignature(GenericSignature *sig);
 

lib/AST/GenericSignatureBuilder.cpp

@@ -2273,9 +2273,8 @@ bool GenericSignatureBuilder::addGenericParameterRequirements(
   auto PA = Impl->PotentialArchetypes[Key.findIndexIn(Impl->GenericParams)];
 
   // Add the requirements from the declaration.
-  llvm::SmallPtrSet<ProtocolDecl *, 8> visited;
   return isErrorResult(
-           addInheritedRequirements(GenericParam, PA, nullptr, visited,
+           addInheritedRequirements(GenericParam, PA, nullptr,
                                     GenericParam->getModuleContext()));
 }
 
@@ -2293,14 +2292,6 @@ void GenericSignatureBuilder::addGenericParameter(GenericTypeParamType *GenericP
   Impl->PotentialArchetypes.push_back(PA);
 }
 
-ConstraintResult GenericSignatureBuilder::addConformanceRequirement(
-                                             PotentialArchetype *PAT,
-                                             ProtocolDecl *Proto,
-                                             const RequirementSource *Source) {
-  llvm::SmallPtrSet<ProtocolDecl *, 8> Visited;
-  return addConformanceRequirement(PAT, Proto, Source, Visited);
-}
-
 /// Visit all of the types that show up in the list of inherited
 /// types.
 static ConstraintResult visitInherited(
@@ -2349,8 +2340,7 @@ static ConstraintResult visitInherited(
 ConstraintResult GenericSignatureBuilder::addConformanceRequirement(
                                PotentialArchetype *PAT,
                                ProtocolDecl *Proto,
-                               const RequirementSource *Source,
-                               llvm::SmallPtrSetImpl<ProtocolDecl *> &Visited) {
+                               const RequirementSource *Source) {
   // Add the requirement, if we haven't done so already.
   if (!PAT->addConformance(Proto, Source, *this))
     return ConstraintResult::Resolved;
@@ -2370,7 +2360,7 @@ ConstraintResult GenericSignatureBuilder::addConformanceRequirement(
                                                         /*inferred=*/false);
     for (auto req : reqSig->getRequirements()) {
       auto reqResult = addRequirement(req, innerSource, nullptr,
-                                      &protocolSubMap, Visited);
+                                      &protocolSubMap);
       if (isErrorResult(reqResult)) return reqResult;
     }
 
@@ -2384,7 +2374,7 @@ ConstraintResult GenericSignatureBuilder::addConformanceRequirement(
   auto protoModule = Proto->getParentModule();
 
   auto inheritedReqResult =
-    addInheritedRequirements(Proto, PAT, Source, Visited, protoModule);
+    addInheritedRequirements(Proto, PAT, Source, protoModule);
   if (isErrorResult(inheritedReqResult))
     return inheritedReqResult;
 
@@ -2403,8 +2393,7 @@ ConstraintResult GenericSignatureBuilder::addConformanceRequirement(
       // Add requirements placed directly on this associated type.
       Type assocType = DependentMemberType::get(concreteSelf, AssocType);
       auto assocResult =
-        addInheritedRequirements(AssocType, assocType, Source, Visited,
-                                 protoModule);
+        addInheritedRequirements(AssocType, assocType, Source, protoModule);
       if (isErrorResult(assocResult))
         return assocResult;
 
@@ -2581,13 +2570,7 @@ ConstraintResult GenericSignatureBuilder::addTypeRequirement(
                              UnresolvedType subject,
                              UnresolvedType constraint,
                              FloatingRequirementSource source,
-                             UnresolvedHandlingKind unresolvedHandling,
-                             llvm::SmallPtrSetImpl<ProtocolDecl *> *visited) {
-  // Make sure we always have a "visited" set to pass down.
-  SmallPtrSet<ProtocolDecl *, 4> visitedSet;
-  if (!visited)
-    visited = &visitedSet;
-
+                             UnresolvedHandlingKind unresolvedHandling) {
   // Resolve the constraint.
   auto resolvedConstraint = resolve(constraint, source);
   if (!resolvedConstraint) {
@@ -2685,7 +2668,7 @@ ConstraintResult GenericSignatureBuilder::addTypeRequirement(
     for (auto *proto : layout.getProtocols()) {
       auto *protoDecl = proto->getDecl();
       if (isErrorResult(addConformanceRequirement(subjectPA, protoDecl,
-                                                  resolvedSource, *visited)))
+                                                  resolvedSource)))
         anyErrors = true;
     }
 
@@ -3031,7 +3014,6 @@ ConstraintResult GenericSignatureBuilder::addInheritedRequirements(
                              TypeDecl *decl,
                              UnresolvedType type,
                              const RequirementSource *parentSource,
-                             llvm::SmallPtrSetImpl<ProtocolDecl *> &visited,
                              ModuleDecl *inferForModule) {
   if (isa<AssociatedTypeDecl>(decl) &&
       decl->hasInterfaceType() &&
@@ -3096,8 +3078,7 @@ ConstraintResult GenericSignatureBuilder::addInheritedRequirements(
     return addTypeRequirement(type, inheritedType,
                               getFloatingSource(typeRepr,
                                                 /*forInferred=*/false),
-                              UnresolvedHandlingKind::GenerateConstraints,
-                              &visited);
+                              UnresolvedHandlingKind::GenerateConstraints);
   };
 
   auto visitLayout = [&](LayoutConstraint layout, const TypeRepr *typeRepr) {
@@ -3206,21 +3187,11 @@ ConstraintResult GenericSignatureBuilder::addRequirement(
   llvm_unreachable("Unhandled requirement?");
 }
 
-ConstraintResult GenericSignatureBuilder::addRequirement(
-                                             const Requirement &req,
-                                             FloatingRequirementSource source,
-                                             ModuleDecl *inferForModule,
-                                             const SubstitutionMap *subMap) {
-  llvm::SmallPtrSet<ProtocolDecl *, 8> visited;
-  return addRequirement(req, source, inferForModule, subMap, visited);
-}
-
 ConstraintResult GenericSignatureBuilder::addRequirement(
                             const Requirement &req,
                             FloatingRequirementSource source,
                             ModuleDecl *inferForModule,
-                            const SubstitutionMap *subMap,
-                            llvm::SmallPtrSetImpl<ProtocolDecl *> &Visited) {
+                            const SubstitutionMap *subMap) {
   auto subst = [&](Type t) {
     if (subMap)
       return t.subst(*subMap);
@@ -3245,8 +3216,7 @@ ConstraintResult GenericSignatureBuilder::addRequirement(
     }
 
     return addTypeRequirement(firstType, secondType, source,
-                              UnresolvedHandlingKind::GenerateConstraints,
-                              &Visited);
+                              UnresolvedHandlingKind::GenerateConstraints);
   }
 
   case RequirementKind::Layout: {