[ABI] Collapse generic witness table into protocol conformance record.

docs/ABI/Mangling.rst

@@ -84,7 +84,7 @@ Globals
   global ::= protocol-conformance 'WP'   // protocol witness table
   global ::= protocol-conformance 'Wa'   // protocol witness table accessor
 
-  global ::= protocol-conformance 'WG'   // generic protocol witness table
+  global ::= protocol-conformance 'WG'   // generic protocol witness table (HISTORICAL)
   global ::= protocol-conformance 'Wp'   // protocol witness table pattern
   global ::= protocol-conformance 'Wr'   // resilient witness table (HISTORICAL)
   global ::= protocol-conformance 'WI'   // generic protocol witness table instantiation function

include/swift/ABI/Metadata.h

@@ -1989,7 +1989,7 @@ struct TargetResilientWitnessTable final
 using ResilientWitnessTable = TargetResilientWitnessTable<InProcess>;
 
 /// \brief The control structure of a generic or resilient protocol
-/// conformance.
+/// conformance, which is embedded in the protocol conformance descriptor.
 ///
 /// Witness tables need to be instantiated at runtime in these cases:
 /// - For a generic conforming type, associated type requirements might be
@@ -2245,14 +2245,16 @@ struct TargetProtocolConformanceDescriptor final
              RelativeContextPointer<Runtime>,
              TargetGenericRequirementDescriptor<Runtime>,
              TargetResilientWitnessesHeader<Runtime>,
-             TargetResilientWitness<Runtime>> {
+             TargetResilientWitness<Runtime>,
+             TargetGenericWitnessTable<Runtime>> {
 
   using TrailingObjects = swift::ABI::TrailingObjects<
                              TargetProtocolConformanceDescriptor<Runtime>,
                              RelativeContextPointer<Runtime>,
                              TargetGenericRequirementDescriptor<Runtime>,
                              TargetResilientWitnessesHeader<Runtime>,
-                             TargetResilientWitness<Runtime>>;
+                             TargetResilientWitness<Runtime>,
+                             TargetGenericWitnessTable<Runtime>>;
   friend TrailingObjects;
 
   template<typename T>
@@ -2268,6 +2270,7 @@ struct TargetProtocolConformanceDescriptor final
 
   using ResilientWitnessesHeader = TargetResilientWitnessesHeader<Runtime>;
   using ResilientWitness = TargetResilientWitness<Runtime>;
+  using GenericWitnessTable = TargetGenericWitnessTable<Runtime>;
 
 private:
   /// The protocol being conformed to.
@@ -2375,6 +2378,14 @@ struct TargetProtocolConformanceDescriptor final
              numTrailingObjects(OverloadToken<ResilientWitness>()));
   }
 
+  ConstTargetPointer<Runtime, GenericWitnessTable>
+  getGenericWitnessTable() const {
+    if (!Flags.hasGenericWitnessTable())
+      return nullptr;
+
+    return this->template getTrailingObjects<GenericWitnessTable>();
+  }
+
 #if !defined(NDEBUG) && SWIFT_OBJC_INTEROP
   void dump() const;
 #endif
@@ -2409,6 +2420,10 @@ struct TargetProtocolConformanceDescriptor final
           ->NumWitnesses
       : 0;
   }
+
+  size_t numTrailingObjects(OverloadToken<GenericWitnessTable>) const {
+    return Flags.hasGenericWitnessTable() ? 1 : 0;
+  }
 };
 using ProtocolConformanceDescriptor
   = TargetProtocolConformanceDescriptor<InProcess>;

include/swift/ABI/MetadataValues.h

@@ -629,6 +629,7 @@ class ConformanceFlags {
     NumConditionalRequirementsShift = 8,
 
     HasResilientWitnessesMask = 0x01 << 16,
+    HasGenericWitnessTableMask = 0x01 << 17,
   };
 
   int_type Value;
@@ -668,6 +669,14 @@ class ConformanceFlags {
                                                     : 0));
   }
 
+  ConformanceFlags withHasGenericWitnessTable(
+                                           bool hasGenericWitnessTable) const {
+    return ConformanceFlags((Value & ~HasGenericWitnessTableMask)
+                            | (hasGenericWitnessTable
+                                 ? HasGenericWitnessTableMask
+                                 : 0));
+  }
+
   /// Retrieve the conformance kind.
   ConformanceKind getConformanceKind() const {
     return ConformanceKind(Value & ConformanceKindMask);
@@ -709,6 +718,12 @@ class ConformanceFlags {
     return Value & HasResilientWitnessesMask;
   }
 
+  /// Whether this conformance has a generic witness table that may need to
+  /// be instantiated.
+  bool hasGenericWitnessTable() const {
+    return Value & HasGenericWitnessTableMask;
+  }
+
   int_type getIntValue() const { return Value; }
 };
 

include/swift/IRGen/Linking.h

@@ -247,10 +247,6 @@ class LinkEntity {
     /// ProtocolConformance*.
     ProtocolWitnessTableAccessFunction,
 
-    /// A generic protocol witness table cache.  The secondary pointer is a
-    /// ProtocolConformance*.
-    GenericProtocolWitnessTableCache,
-
     /// The instantiation function for a generic protocol witness table.
     /// The secondary pointer is a ProtocolConformance*.
     GenericProtocolWitnessTableInstantiationFunction,
@@ -738,13 +734,6 @@ class LinkEntity {
     return entity;
   }
 
-  static LinkEntity
-  forGenericProtocolWitnessTableCache(const ProtocolConformance *C) {
-    LinkEntity entity;
-    entity.setForProtocolConformance(Kind::GenericProtocolWitnessTableCache, C);
-    return entity;
-  }
-
   static LinkEntity
   forGenericProtocolWitnessTableInstantiationFunction(
                                       const ProtocolConformance *C) {

include/swift/Runtime/Metadata.h

@@ -387,10 +387,10 @@ MetadataResponse swift_checkMetadataState(MetadataRequest request,
 
 /// Instantiate a resilient or generic protocol witness table.
 ///
-/// \param genericTable - The witness table template for the
-///   conformance. It may either have fields that require runtime
-///   initialization, or be missing requirements at the end for
-///   which default witnesses are available.
+/// \param conformance - The protocol conformance descriptor, which
+///   contains the generic witness table record. It may either have fields
+///   that require runtime initialization, or be missing requirements at the
+///   end for which default witnesses are available.
 ///
 /// \param type - The conforming type, used to form a uniquing key
 ///   for the conformance. If the witness table is not dependent on
@@ -406,9 +406,9 @@ MetadataResponse swift_checkMetadataState(MetadataRequest request,
 ///   conformances.
 SWIFT_RUNTIME_EXPORT
 const WitnessTable *
-swift_getGenericWitnessTable(GenericWitnessTable *genericTable,
-                             const Metadata *type,
-                             void **const *instantiationArgs);
+swift_instantiateWitnessTable(ProtocolConformanceDescriptor *conformance,
+                              const Metadata *type,
+                              void **const *instantiationArgs);
 
 /// Retrieve an associated type witness from the given witness table.
 ///

include/swift/Runtime/RuntimeFunctions.def

@@ -635,12 +635,12 @@ FUNCTION(CheckMetadataState, swift_checkMetadataState, SwiftCC,
          ATTRS(NoUnwind, ReadOnly))
 
 // const ProtocolWitnessTable *
-// swift_getGenericWitnessTable(GenericProtocolWitnessTable *genericTable,
-//                              const Metadata *type,
-//                              void ** const *instantiationArgs);
-FUNCTION(GetGenericWitnessTable, swift_getGenericWitnessTable, C_CC,
+// swift_instantiateWitnessTable(const ProtocolConformanceDescriptor *conf,
+//                               const Metadata *type,
+//                               void ** const *instantiationArgs);
+FUNCTION(InstantiateWitnessTable, swift_instantiateWitnessTable, C_CC,
          RETURNS(WitnessTablePtrTy),
-         ARGS(getGenericWitnessTableCacheTy()->getPointerTo(),
+         ARGS(ProtocolConformanceDescriptorPtrTy,
               TypeMetadataPtrTy,
               WitnessTablePtrPtrTy),
          ATTRS(NoUnwind, ReadOnly))

lib/IRGen/GenDecl.cpp

@@ -3644,15 +3644,6 @@ IRGenModule::getResilienceExpansionForLayout(SILGlobalVariable *global) {
   return ResilienceExpansion::Maximal;
 }
 
-llvm::Constant *IRGenModule::
-getAddrOfGenericWitnessTableCache(const NormalProtocolConformance *conf,
-                                  ForDefinition_t forDefinition) {
-  auto entity = LinkEntity::forGenericProtocolWitnessTableCache(conf);
-  auto expectedTy = getGenericWitnessTableCacheTy();
-  return getAddrOfLLVMVariable(entity, getPointerAlignment(), forDefinition,
-                               expectedTy, DebugTypeInfo());
-}
-
 llvm::Function *
 IRGenModule::getAddrOfGenericWitnessTableInstantiationFunction(
                                       const NormalProtocolConformance *conf) {
@@ -3675,25 +3666,6 @@ IRGenModule::getAddrOfGenericWitnessTableInstantiationFunction(
   return entry;
 }
 
-llvm::StructType *IRGenModule::getGenericWitnessTableCacheTy() {
-  if (auto ty = GenericWitnessTableCacheTy) return ty;
-
-  GenericWitnessTableCacheTy = llvm::StructType::create(getLLVMContext(),
-    {
-      // WitnessTableSizeInWords
-      Int16Ty,
-      // WitnessTablePrivateSizeInWords + RequiresInstantiation bit
-      Int16Ty,
-      // Pattern
-      RelativeAddressTy,
-      // Instantiator
-      RelativeAddressTy,
-      // PrivateData
-      RelativeAddressTy
-    }, "swift.generic_witness_table_cache");
-  return GenericWitnessTableCacheTy;
-}
-
 /// Fetch the witness table access function for a protocol conformance.
 llvm::Function *
 IRGenModule::getAddrOfWitnessTableAccessFunction(