[Serialization] Collapse indirection in DeclContextID

include/swift/Serialization/DeclTypeRecordNodes.def

@@ -149,7 +149,7 @@ PATTERN(VAR)
 OTHER(PARAMETERLIST, 210)
 // 211 is unused
 OTHER(FOREIGN_ERROR_CONVENTION, 212)
-OTHER(DECL_CONTEXT, 213)
+// 213 is unused
 OTHER(XREF_TYPE_PATH_PIECE, 214)
 OTHER(XREF_VALUE_PATH_PIECE, 215)
 OTHER(XREF_EXTENSION_PATH_PIECE, 216)

include/swift/Serialization/ModuleFile.h

@@ -305,9 +305,6 @@ class ModuleFile
   /// Decls referenced by this module.
   MutableArrayRef<Serialized<Decl*>> Decls;
 
-  /// DeclContexts referenced by this module.
-  MutableArrayRef<Serialized<DeclContext*>> DeclContexts;
-
   /// Local DeclContexts referenced by this module.
   MutableArrayRef<Serialized<DeclContext*>> LocalDeclContexts;
 
@@ -862,7 +859,7 @@ class ModuleFile
   DeclContext *getDeclContext(serialization::DeclContextID DID);
 
   /// Returns the local decl context with the given ID, deserializing it if needed.
-  DeclContext *getLocalDeclContext(serialization::DeclContextID DID);
+  DeclContext *getLocalDeclContext(serialization::LocalDeclContextID DID);
 
   /// Returns the appropriate module for the given ID.
   ModuleDecl *getModule(serialization::ModuleID MID);

include/swift/Serialization/ModuleFormat.h

@@ -52,7 +52,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 514; // specialize attr
+const uint16_t SWIFTMODULE_VERSION_MINOR = 515; // remove DeclContext indirection
 
 using DeclIDField = BCFixed<31>;
 
@@ -66,9 +66,58 @@ using TypeIDWithBitField = BCFixed<32>;
 using IdentifierID = DeclID;
 using IdentifierIDField = DeclIDField;
 
-// DeclContextID must be the same as DeclID because it is stored in the same way.
-using DeclContextID = DeclID;
-using DeclContextIDField = DeclIDField;
+// LocalDeclContextID must be the same as DeclID because it is stored in the
+// same way.
+using LocalDeclContextID = DeclID;
+using LocalDeclContextIDField = DeclIDField;
+
+/// Stores either a DeclID or a LocalDeclContextID, using 32 bits.
+class DeclContextID {
+  int32_t rawValue;
+  explicit DeclContextID(int32_t rawValue) : rawValue(rawValue) {}
+public:
+  DeclContextID() : DeclContextID(0) {}
+
+  static DeclContextID forDecl(DeclID value) {
+    assert(value && "should encode null using DeclContextID()");
+    assert(llvm::isUInt<31>(value) && "too many DeclIDs");
+    return DeclContextID(static_cast<int32_t>(value));
+  }
+  static DeclContextID forLocalDeclContext(LocalDeclContextID value) {
+    assert(value && "should encode null using DeclContextID()");
+    assert(llvm::isUInt<31>(value) && "too many LocalDeclContextIDs");
+    return DeclContextID(-static_cast<int32_t>(value));
+  }
+
+  explicit operator bool() const {
+    return rawValue != 0;
+  }
+
+  Optional<DeclID> getAsDeclID() const {
+    if (rawValue > 0)
+      return DeclID(rawValue);
+    return None;
+  }
+
+  Optional<LocalDeclContextID> getAsLocalDeclContextID() const {
+    if (rawValue < 0)
+      return LocalDeclContextID(-rawValue);
+    return None;
+  }
+
+  static DeclContextID getFromOpaqueValue(uint32_t opaqueValue) {
+    return DeclContextID(opaqueValue);
+  }
+  uint32_t getOpaqueValue() const { return rawValue; }
+};
+
+class DeclContextIDField : public BCFixed<32> {
+public:
+  static DeclContextID convert(uint64_t rawValue) {
+    assert(llvm::isUInt<32>(rawValue));
+    return DeclContextID::getFromOpaqueValue(rawValue);
+  }
+};
 
 // NormalConformanceID must be the same as DeclID because it is stored
 // in the same way.
@@ -1154,7 +1203,7 @@ namespace decls_block {
     StaticSpellingKindField, // spelling of 'static' or 'class'
     BCVBR<3>,    // numpatterns
     BCArray<DeclContextIDField> // init contexts
-    // The patterns and decl-contexts trail the record.
+    // The patterns trail the record.
   >;
 
   template <unsigned Code>
@@ -1520,16 +1569,6 @@ namespace decls_block {
     BCFixed<2>  // modref value
   >;
 
-  using DeclContextLayout = BCRecordLayout<
-    DECL_CONTEXT,
-    // If this DeclContext is a local context, this is an
-    // index into the local decl context table.
-    // If this DeclContext is a Decl (and not a DeclContext
-    // *at all*, this is an index into the decl table.
-    DeclContextIDField,
-    BCFixed<1> // is a decl
-  >;
-
   using ForeignErrorConventionLayout = BCRecordLayout<
     FOREIGN_ERROR_CONVENTION,
     ForeignErrorConventionKindField,  // kind
@@ -1739,7 +1778,6 @@ namespace index_block {
 
     ENTRY_POINT,
     LOCAL_DECL_CONTEXT_OFFSETS,
-    DECL_CONTEXT_OFFSETS,
     LOCAL_TYPE_DECLS,
     OPAQUE_RETURN_TYPE_DECLS,
     GENERIC_ENVIRONMENT_OFFSETS,

lib/Serialization/Deserialization.cpp

@@ -1805,7 +1805,7 @@ StringRef ModuleFile::getIdentifierText(IdentifierID IID) {
   return rawStrPtr.slice(0, terminatorOffset);
 }
 
-DeclContext *ModuleFile::getLocalDeclContext(DeclContextID DCID) {
+DeclContext *ModuleFile::getLocalDeclContext(LocalDeclContextID DCID) {
   assert(DCID != 0 && "invalid local DeclContext ID 0");
   auto &declContextOrOffset = LocalDeclContexts[DCID-1];
 
@@ -1893,56 +1893,24 @@ DeclContext *ModuleFile::getLocalDeclContext(DeclContextID DCID) {
 }
 
 DeclContext *ModuleFile::getDeclContext(DeclContextID DCID) {
-  if (DCID == 0)
+  if (!DCID)
     return FileContext;
 
-  assert(DCID <= DeclContexts.size() && "invalid DeclContext ID");
-  auto &declContextOrOffset = DeclContexts[DCID-1];
+  if (Optional<LocalDeclContextID> contextID = DCID.getAsLocalDeclContextID())
+    return getLocalDeclContext(contextID.getValue());
 
-  if (declContextOrOffset.isComplete())
-    return declContextOrOffset;
-
-  BCOffsetRAII restoreOffset(DeclTypeCursor);
-  DeclTypeCursor.JumpToBit(declContextOrOffset);
-  auto entry = DeclTypeCursor.advance();
+  auto D = getDecl(DCID.getAsDeclID().getValue());
 
-  if (entry.Kind != llvm::BitstreamEntry::Record)
-    fatal();
-
-  SmallVector<uint64_t, 64> scratch;
-  StringRef blobData;
+  if (auto GTD = dyn_cast<GenericTypeDecl>(D))
+    return GTD;
+  if (auto ED = dyn_cast<ExtensionDecl>(D))
+    return ED;
+  if (auto AFD = dyn_cast<AbstractFunctionDecl>(D))
+    return AFD;
+  if (auto SD = dyn_cast<SubscriptDecl>(D))
+    return SD;
 
-  unsigned recordID = DeclTypeCursor.readRecord(entry.ID, scratch, &blobData);
-
-  if (recordID != decls_block::DECL_CONTEXT)
-    llvm_unreachable("Expected a DECL_CONTEXT record");
-
-  DeclContextID declOrDeclContextId;
-  bool isDecl;
-
-  decls_block::DeclContextLayout::readRecord(scratch, declOrDeclContextId,
-                                             isDecl);
-
-  if (!isDecl)
-    return getLocalDeclContext(declOrDeclContextId);
-
-  auto D = getDecl(declOrDeclContextId);
-
-  if (auto ND = dyn_cast<NominalTypeDecl>(D)) {
-    declContextOrOffset = ND;
-  } else if (auto ED = dyn_cast<ExtensionDecl>(D)) {
-    declContextOrOffset = ED;
-  } else if (auto AFD = dyn_cast<AbstractFunctionDecl>(D)) {
-    declContextOrOffset = AFD;
-  } else if (auto SD = dyn_cast<SubscriptDecl>(D)) {
-    declContextOrOffset = SD;
-  } else if (auto TAD = dyn_cast<TypeAliasDecl>(D)) {
-    declContextOrOffset = TAD;
-  } else {
-    llvm_unreachable("Unknown Decl : DeclContext kind");
-  }
-
-  return declContextOrOffset;
+  llvm_unreachable("Unknown Decl : DeclContext kind");
 }
 
 ModuleDecl *ModuleFile::getModule(ModuleID MID) {
@@ -3195,8 +3163,10 @@ class swift::DeclDeserializer {
       }
 
       patterns.emplace_back(pattern.get(), DeclContextID());
-      if (!initContextIDs.empty())
-        patterns.back().second = initContextIDs[i];
+      if (!initContextIDs.empty()) {
+        patterns.back().second =
+            DeclContextID::getFromOpaqueValue(initContextIDs[i]);
+      }
     }
 
     auto binding =

lib/Serialization/ModuleFile.cpp

@@ -874,10 +874,6 @@ bool ModuleFile::readIndexBlock(llvm::BitstreamCursor &cursor) {
         assert(blobData.empty());
         allocateBuffer(Decls, scratch);
         break;
-      case index_block::DECL_CONTEXT_OFFSETS:
-        assert(blobData.empty());
-        allocateBuffer(DeclContexts, scratch);
-        break;
       case index_block::TYPE_OFFSETS:
         assert(blobData.empty());
         allocateBuffer(Types, scratch);