[IRGen] Simplify the ownership of ProtocolInfo (#18704)

Rather than keep a singly-linked list of ProtocolInfo objects to free,
just rely on them being cached in the single DenseMap in
TypeConverter.

Author: jrose-apple

lib/IRGen/GenProto.cpp

@@ -2109,18 +2109,17 @@ const ProtocolInfo &TypeConverter::getProtocolInfo(ProtocolDecl *protocol,
                                                    ProtocolInfoKind kind) {
   // Check whether we've already translated this protocol.
   auto it = Protocols.find(protocol);
-  if (it != Protocols.end() && it->second->getKind() >= kind)
-    return *it->second;
+  if (it != Protocols.end() && it->getSecond()->getKind() >= kind)
+    return *it->getSecond();
 
   // If not, lay out the protocol's witness table, if it needs one.
   WitnessTableLayout layout(kind);
   if (Lowering::TypeConverter::protocolRequiresWitnessTable(protocol))
     layout.visitProtocolDecl(protocol);
 
   // Create a ProtocolInfo object from the layout.
-  ProtocolInfo *info = ProtocolInfo::create(layout.getEntries(), kind);
-  info->NextConverted.setPointer(FirstProtocol);
-  FirstProtocol = info;
+  std::unique_ptr<ProtocolInfo> info = ProtocolInfo::create(layout.getEntries(),
+                                                            kind);
 
   // Verify that we haven't generated an incompatible layout.
   if (it != Protocols.end()) {
@@ -2134,18 +2133,19 @@ const ProtocolInfo &TypeConverter::getProtocolInfo(ProtocolDecl *protocol,
   }
 
   // Memoize.
-  Protocols[protocol] = info;
+  std::unique_ptr<const ProtocolInfo> &cachedInfo = Protocols[protocol];
+  cachedInfo = std::move(info);
 
   // Done.
-  return *info;
+  return *cachedInfo;
 }
 
 /// Allocate a new ProtocolInfo.
-ProtocolInfo *ProtocolInfo::create(ArrayRef<WitnessTableEntry> table,
-                                   ProtocolInfoKind kind) {
+std::unique_ptr<ProtocolInfo>
+ProtocolInfo::create(ArrayRef<WitnessTableEntry> table, ProtocolInfoKind kind) {
   size_t bufferSize = totalSizeToAlloc<WitnessTableEntry>(table.size());
   void *buffer = ::operator new(bufferSize);
-  return new(buffer) ProtocolInfo(table, kind);
+  return std::unique_ptr<ProtocolInfo>(new(buffer) ProtocolInfo(table, kind));
 }
 
 // Provide a unique home for the ConformanceInfo vtable.

lib/IRGen/GenType.cpp

@@ -1078,12 +1078,6 @@ TypeConverter::~TypeConverter() {
     I = Cur->NextConverted;
     delete Cur;
   }
-  
-  for (const ProtocolInfo *I = FirstProtocol; I != nullptr; ) {
-    const ProtocolInfo *Cur = I;
-    I = Cur->NextConverted.getPointer();
-    delete Cur;
-  }
 }
 
 void TypeConverter::pushGenericContext(CanGenericSignature signature) {

lib/IRGen/GenType.h

@@ -67,10 +67,9 @@ class TypeConverter {
 private:
   bool CompletelyFragile = false;
 
-  llvm::DenseMap<ProtocolDecl*, const ProtocolInfo*> Protocols;
+  llvm::DenseMap<ProtocolDecl*, std::unique_ptr<const ProtocolInfo>> Protocols;
   const TypeInfo *FirstType;
 
-  const ProtocolInfo *FirstProtocol = nullptr;
   const LoadableTypeInfo *NativeObjectTI = nullptr;
   const LoadableTypeInfo *UnknownObjectTI = nullptr;
   const LoadableTypeInfo *BridgeObjectTI = nullptr;

lib/IRGen/ProtocolInfo.h

@@ -165,26 +165,25 @@ enum class ProtocolInfoKind : uint8_t {
 class ProtocolInfo final :
     private llvm::TrailingObjects<ProtocolInfo, WitnessTableEntry> {
   friend TrailingObjects;
-
-  /// A singly-linked-list of all the protocols that have been laid out.
-  llvm::PointerIntPair<const ProtocolInfo *, 1, ProtocolInfoKind> NextConverted;
   friend class TypeConverter;
 
-  ProtocolInfoKind getKind() const {
-    return NextConverted.getInt();
-  }
-
   /// The number of table entries in this protocol layout.
   unsigned NumTableEntries;
 
+  ProtocolInfoKind Kind;
+
+  ProtocolInfoKind getKind() const {
+    return Kind;
+  }
+
   ProtocolInfo(ArrayRef<WitnessTableEntry> table, ProtocolInfoKind kind)
-      : NextConverted(nullptr, kind), NumTableEntries(table.size()) {
+      : NumTableEntries(table.size()), Kind(kind) {
     std::uninitialized_copy(table.begin(), table.end(),
                             getTrailingObjects<WitnessTableEntry>());
   }
 
-  static ProtocolInfo *create(ArrayRef<WitnessTableEntry> table,
-                              ProtocolInfoKind kind);
+  static std::unique_ptr<ProtocolInfo> create(ArrayRef<WitnessTableEntry> table,
+                                              ProtocolInfoKind kind);
 
 public:
   /// The number of witness slots in a conformance to this protocol;