[Serialization] Remove "delayed actions" support

Previously, cycle-breaking logic would delay certain actions until all
re-entrant deserialization was complete for a particular module. That
hasn't been used in a while, though, now that the AST itself supports
more laziness, so let's take it out.

No functionality change; this really was unused.

Author: jrose-apple

include/swift/Serialization/ModuleFile.h

@@ -87,46 +87,11 @@ class ModuleFile
   /// A callback to be invoked every time a type was deserialized.
   std::function<void(Type)> DeserializedTypeCallback;
 
-  /// The number of entities that are currently being deserialized.
-  unsigned NumCurrentDeserializingEntities = 0;
-
   /// Is this module file actually a .sib file? .sib files are serialized SIL at
   /// arbitrary granularity and arbitrary stage; unlike serialized Swift
   /// modules, which are assumed to contain canonical SIL for an entire module.
   bool IsSIB = false;
 
-  /// RAII class to be used when deserializing an entity.
-  class DeserializingEntityRAII {
-    ModuleFile &MF;
-
-  public:
-    DeserializingEntityRAII(ModuleFile &mf)
-        : MF(mf.getModuleFileForDelayedActions()) {
-      ++MF.NumCurrentDeserializingEntities;
-    }
-    ~DeserializingEntityRAII() {
-      assert(MF.NumCurrentDeserializingEntities > 0 &&
-             "Imbalanced currently-deserializing count?");
-      if (MF.NumCurrentDeserializingEntities == 1) {
-        MF.finishPendingActions();
-      }
-
-      --MF.NumCurrentDeserializingEntities;
-    }
-  };
-  friend class DeserializingEntityRAII;
-
-  /// Picks a specific ModuleFile instance to serve as the "delayer" for the
-  /// entire module.
-  ///
-  /// This is usually \c this, but when there are partial swiftmodules all
-  /// loaded for the same module it may be different.
-  ModuleFile &getModuleFileForDelayedActions();
-
-  /// Finish any pending actions that were waiting for the topmost entity to
-  /// be deserialized.
-  void finishPendingActions();
-
 public:
   /// Represents another module that has been imported as a dependency.
   class Dependency {

lib/Serialization/Deserialization.cpp

@@ -182,26 +182,6 @@ void ModuleFile::fatal(llvm::Error error) {
   abort();
 }
 
-ModuleFile &ModuleFile::getModuleFileForDelayedActions() {
-  assert(FileContext && "cannot delay actions before associating with a file");
-  ModuleDecl *associatedModule = getAssociatedModule();
-
-  // Check for the common case.
-  if (associatedModule->getFiles().size() == 1)
-    return *this;
-
-  for (FileUnit *file : associatedModule->getFiles())
-    if (auto *serialized = dyn_cast<SerializedASTFile>(file))
-      return serialized->File;
-
-  llvm_unreachable("should always have FileContext in the list of files");
-}
-
-void ModuleFile::finishPendingActions() {
-  assert(&getModuleFileForDelayedActions() == this &&
-         "wrong module used for delayed actions");
-}
-
 static Optional<swift::AccessorKind>
 getActualAccessorKind(uint8_t raw) {
   switch (serialization::AccessorKind(raw)) {
@@ -883,7 +863,6 @@ GenericSignature *ModuleFile::getGenericSignature(
   // Read the generic signature.
   BCOffsetRAII restoreOffset(DeclTypeCursor);
   DeclTypeCursor.JumpToBit(sigOrOffset);
-  DeserializingEntityRAII deserializingEntity(*this);
 
   // Read the parameter types.
   SmallVector<GenericTypeParamType *, 4> paramTypes;
@@ -959,7 +938,6 @@ ModuleFile::getGenericSignatureOrEnvironment(
     // Read the generic environment.
     BCOffsetRAII restoreOffset(DeclTypeCursor);
     DeclTypeCursor.JumpToBit(bitOffset);
-    DeserializingEntityRAII deserializingEntity(*this);
 
     SmallVector<GenericTypeParamType *, 4> paramTypes;
     using namespace decls_block;
@@ -1067,7 +1045,6 @@ SubstitutionMap ModuleFile::getSubstitutionMap(
   // Read the substitution map.
   BCOffsetRAII restoreOffset(DeclTypeCursor);
   DeclTypeCursor.JumpToBit(substitutionsOrOffset);
-  DeserializingEntityRAII deserializingEntity(*this);
 
   // Read the substitution map.
   auto entry = DeclTypeCursor.advance(AF_DontPopBlockAtEnd);
@@ -4007,7 +3984,6 @@ ModuleFile::getDeclChecked(DeclID DID) {
     BCOffsetRAII restoreOffset(DeclTypeCursor);
     DeclTypeCursor.JumpToBit(declOrOffset);
 
-    ModuleFile::DeserializingEntityRAII deserializingEntity(*this);
     Expected<Decl *> deserialized =
       DeclDeserializer(*this, declOrOffset).getDeclCheckedImpl();
     if (!deserialized)