[Serialization] Simplify the representation of GenericParamLists (swiftlang#20446)

Now that we don't store requirements in the GenericParamList, there's
no reason to use trailing records to list out the
GenericTypeParamDecls.

No functionality change.

Author: jrose-apple

include/swift/Serialization/DeclTypeRecordNodes.def

@@ -159,10 +159,10 @@ OTHER(DEFAULT_ARGUMENT_INITIALIZER_CONTEXT, 222)
 OTHER(TOP_LEVEL_CODE_DECL_CONTEXT, 223)
 
 OTHER(GENERIC_PARAM_LIST, 230)
-TRAILING_INFO(GENERIC_PARAM)
+OTHER(GENERIC_SIGNATURE, 231)
 TRAILING_INFO(GENERIC_REQUIREMENT)
 TRAILING_INFO(LAYOUT_REQUIREMENT)
-OTHER(GENERIC_SIGNATURE, 234)
+// 234 is unused
 OTHER(SIL_GENERIC_ENVIRONMENT, 235)
 OTHER(SUBSTITUTION_MAP, 236)
 

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 = 463; // Last change: enable-private-imports
+const uint16_t SWIFTMODULE_VERSION_MINOR = 464; // Last change: simplify GenericParamLists
 
 using DeclIDField = BCFixed<31>;
 
@@ -1259,13 +1259,8 @@ namespace decls_block {
   >;
 
   using GenericParamListLayout = BCRecordLayout<
-    GENERIC_PARAM_LIST
-    // The actual parameters and requirements trail the record.
-  >;
-
-  using GenericParamLayout = BCRecordLayout<
-    GENERIC_PARAM,
-    DeclIDField // Typealias
+    GENERIC_PARAM_LIST,
+    BCArray<DeclIDField>        // the GenericTypeParamDecls
   >;
 
   using GenericSignatureLayout = BCRecordLayout<

lib/Serialization/Deserialization.cpp

@@ -652,39 +652,19 @@ GenericParamList *ModuleFile::maybeReadGenericParams(DeclContext *DC,
   unsigned kind = DeclTypeCursor.readRecord(next.ID, scratch, &blobData);
   if (kind != GENERIC_PARAM_LIST)
     return nullptr;
+  lastRecordOffset.reset();
 
   SmallVector<GenericTypeParamDecl *, 8> params;
 
-  while (true) {
-    lastRecordOffset.reset();
-    bool shouldContinue = true;
-
-    auto entry = DeclTypeCursor.advance(AF_DontPopBlockAtEnd);
-    if (entry.Kind != llvm::BitstreamEntry::Record)
-      break;
-
-    scratch.clear();
-    unsigned recordID = DeclTypeCursor.readRecord(entry.ID, scratch,
-                                                  &blobData);
-    switch (recordID) {
-    case GENERIC_PARAM: {
-      DeclID paramDeclID;
-      GenericParamLayout::readRecord(scratch, paramDeclID);
-      auto genericParam = cast<GenericTypeParamDecl>(getDecl(paramDeclID));
-      params.push_back(genericParam);
-      break;
-    }
-    default:
-      // This record is not part of the GenericParamList.
-      shouldContinue = false;
-      break;
-    }
-
-    if (!shouldContinue)
-      break;
+  ArrayRef<uint64_t> paramIDs;
+  GenericParamListLayout::readRecord(scratch, paramIDs);
+  for (DeclID nextParamID : paramIDs) {
+    auto genericParam = cast<GenericTypeParamDecl>(getDecl(nextParamID));
+    params.push_back(genericParam);
   }
 
-  // Don't create empty generic parameter lists.
+  // Don't create empty generic parameter lists. (This should never happen in
+  // practice, but it doesn't hurt to be defensive.)
   if (params.empty())
     return nullptr;
 

lib/Serialization/SILFormat.h

@@ -181,7 +181,6 @@ namespace sil_block {
     INHERITED_PROTOCOL_CONFORMANCE
       = decls_block::INHERITED_PROTOCOL_CONFORMANCE,
     INVALID_PROTOCOL_CONFORMANCE = decls_block::INVALID_PROTOCOL_CONFORMANCE,
-    GENERIC_PARAM = decls_block::GENERIC_PARAM,
     GENERIC_REQUIREMENT = decls_block::GENERIC_REQUIREMENT,
     LAYOUT_REQUIREMENT = decls_block::LAYOUT_REQUIREMENT,
   };

lib/Serialization/Serialization.cpp

@@ -915,8 +915,6 @@ void Serializer::writeBlockInfoBlock() {
                               decls_block::PROTOCOL_CONFORMANCE_XREF);
   BLOCK_RECORD_WITH_NAMESPACE(sil_block,
                               decls_block::GENERIC_PARAM_LIST);
-  BLOCK_RECORD_WITH_NAMESPACE(sil_block,
-                              decls_block::GENERIC_PARAM);
   BLOCK_RECORD_WITH_NAMESPACE(sil_block,
                               decls_block::GENERIC_REQUIREMENT);
   BLOCK_RECORD_WITH_NAMESPACE(sil_block,
@@ -1372,23 +1370,19 @@ void Serializer::writeInlinableBodyTextIfNeeded(
   InlinableBodyTextLayout::emitRecord(Out, ScratchRecord, abbrCode, body);
 }
 
-bool Serializer::writeGenericParams(const GenericParamList *genericParams) {
+void Serializer::writeGenericParams(const GenericParamList *genericParams) {
   using namespace decls_block;
 
   // Don't write anything if there are no generic params.
   if (!genericParams)
-    return true;
-
-  unsigned abbrCode = DeclTypeAbbrCodes[GenericParamListLayout::Code];
-  GenericParamListLayout::emitRecord(Out, ScratchRecord, abbrCode);
+    return;
 
-  abbrCode = DeclTypeAbbrCodes[GenericParamLayout::Code];
-  for (auto next : genericParams->getParams()) {
-    GenericParamLayout::emitRecord(Out, ScratchRecord, abbrCode,
-                                   addDeclRef(next));
-  }
+  SmallVector<DeclID, 4> paramIDs;
+  for (auto next : genericParams->getParams())
+    paramIDs.push_back(addDeclRef(next));
 
-  return true;
+  unsigned abbrCode = DeclTypeAbbrCodes[GenericParamListLayout::Code];
+  GenericParamListLayout::emitRecord(Out, ScratchRecord, abbrCode, paramIDs);
 }
 
 void Serializer::writeGenericSignature(const GenericSignature *sig) {
@@ -4131,10 +4125,9 @@ void Serializer::writeAllDeclsAndTypes() {
   registerDeclTypeAbbr<TypedPatternLayout>();
   registerDeclTypeAbbr<InlinableBodyTextLayout>();
   registerDeclTypeAbbr<GenericParamListLayout>();
-  registerDeclTypeAbbr<GenericParamLayout>();
+  registerDeclTypeAbbr<GenericSignatureLayout>();
   registerDeclTypeAbbr<GenericRequirementLayout>();
   registerDeclTypeAbbr<LayoutRequirementLayout>();
-  registerDeclTypeAbbr<GenericSignatureLayout>();
   registerDeclTypeAbbr<SILGenericEnvironmentLayout>();
   registerDeclTypeAbbr<SubstitutionMapLayout>();
 

lib/Serialization/Serialization.h

@@ -342,8 +342,8 @@ class Serializer : public SerializerBase {
   /// Writes the given pattern, recursively.
   void writePattern(const Pattern *pattern, DeclContext *owningDC);
 
-  /// Writes a generic parameter list.
-  bool writeGenericParams(const GenericParamList *genericParams);
+  /// Writes a generic parameter list, if non-null.
+  void writeGenericParams(const GenericParamList *genericParams);
 
   /// Writes the body text of the provided funciton, if the function is
   /// inlinable and has body text.