Merge pull request #14016 from DougGregor/conformance-descriptor-in-witness-table

[ABI] Add the protocol conformance descriptor into a witness table.

Author: DougGregor

include/swift/ABI/MetadataValues.h

@@ -916,6 +916,9 @@ static inline bool isValueWitnessTableMutable(EnumLayoutFlags flags) {
 /// mutate the array to fill in the direct arguments.
 constexpr unsigned NumDirectGenericTypeMetadataAccessFunctionArgs = 3;
 
+/// The offset (in pointers) to the first requirement in a witness table.
+constexpr unsigned WitnessTableFirstRequirementOffset = 1;
+
 } // end namespace swift
 
 #endif /* SWIFT_ABI_METADATAVALUES_H */

include/swift/Runtime/Metadata.h

@@ -177,6 +177,8 @@ class WeakReference;
 template <typename Runtime> struct TargetMetadata;
 using Metadata = TargetMetadata<InProcess>;
 
+template <typename Runtime> struct TargetProtocolConformanceDescriptor;
+
 /// Storage for an arbitrary value.  In C/C++ terms, this is an
 /// 'object', because it is rooted in memory.
 ///
@@ -2204,10 +2206,19 @@ struct TargetProtocolDescriptor {
 };
 using ProtocolDescriptor = TargetProtocolDescriptor<InProcess>;
 
-/// A witness table for a protocol. This type is intentionally opaque because
+/// A witness table for a protocol.
+///
+/// With the exception of the initial protocol conformance descriptor,
 /// the layout of a witness table is dependent on the protocol being
 /// represented.
-struct WitnessTable;
+template <typename Runtime>
+struct TargetWitnessTable {
+  /// The protocol conformance descriptor from which this witness table
+  /// was generated.
+  const TargetProtocolConformanceDescriptor<Runtime> *Description;
+};
+
+using WitnessTable = TargetWitnessTable<InProcess>;
 
 /// The basic layout of an opaque (non-class-bounded) existential type.
 template <typename Runtime>
@@ -2216,12 +2227,13 @@ struct TargetOpaqueExistentialContainer {
   const TargetMetadata<Runtime> *Type;
   // const void *WitnessTables[];
 
-  const WitnessTable **getWitnessTables() {
-    return reinterpret_cast<const WitnessTable **>(this + 1);
+  const TargetWitnessTable<Runtime> **getWitnessTables() {
+    return reinterpret_cast<const TargetWitnessTable<Runtime> **>(this + 1);
   }
 
-  const WitnessTable * const *getWitnessTables() const {
-    return reinterpret_cast<const WitnessTable * const *>(this + 1);
+  const TargetWitnessTable<Runtime> * const *getWitnessTables() const {
+    return reinterpret_cast<const TargetWitnessTable<Runtime> * const *>(
+                                                                      this + 1);
   }
 
   void copyTypeInto(swift::TargetOpaqueExistentialContainer<Runtime> *dest,
@@ -2305,8 +2317,9 @@ struct TargetExistentialTypeMetadata : public TargetMetadata<Runtime> {
 
   /// Get a witness table from an existential container of the type described
   /// by this metadata.
-  const WitnessTable * getWitnessTable(const OpaqueValue *container,
-                                       unsigned i) const;
+  const TargetWitnessTable<Runtime> * getWitnessTable(
+                                                  const OpaqueValue *container,
+                                                  unsigned i) const;
 
   /// Return true iff all the protocol constraints are @objc.
   bool isObjC() const {
@@ -2345,11 +2358,11 @@ template <typename Runtime>
 struct TargetExistentialMetatypeContainer {
   const TargetMetadata<Runtime> *Value;
 
-  const WitnessTable **getWitnessTables() {
-    return reinterpret_cast<const WitnessTable**>(this + 1);
+  const TargetWitnessTable<Runtime> **getWitnessTables() {
+    return reinterpret_cast<const TargetWitnessTable<Runtime>**>(this + 1);
   }
-  const WitnessTable * const *getWitnessTables() const {
-    return reinterpret_cast<const WitnessTable* const *>(this + 1);
+  const TargetWitnessTable<Runtime> * const *getWitnessTables() const {
+    return reinterpret_cast<const TargetWitnessTable<Runtime>* const *>(this + 1);
   }
 
   void copyTypeInto(TargetExistentialMetatypeContainer *dest,
@@ -2532,10 +2545,10 @@ struct TargetGenericWitnessTable {
                               /*nullable*/ true> Protocol;
 
   /// The pattern.
-  RelativeDirectPointer<const WitnessTable> Pattern;
+  RelativeDirectPointer<const TargetWitnessTable<Runtime>> Pattern;
 
   /// The instantiation function, which is called after the template is copied.
-  RelativeDirectPointer<void(WitnessTable *instantiatedTable,
+  RelativeDirectPointer<void(TargetWitnessTable<Runtime> *instantiatedTable,
                              const TargetMetadata<Runtime> *type,
                              void * const *instantiationArgs),
                         /*nullable*/ true> Instantiator;
@@ -2609,9 +2622,9 @@ template <typename Runtime>
 struct TargetProtocolConformanceDescriptor {
 public:
   using WitnessTableAccessorFn
-    = const WitnessTable *(const TargetMetadata<Runtime>*,
-                           const WitnessTable **,
-                           size_t);
+    = const TargetWitnessTable<Runtime> *(const TargetMetadata<Runtime>*,
+                                          const TargetWitnessTable<Runtime> **,
+                                          size_t);
 
 private:
   /// The protocol being conformed to.
@@ -2637,7 +2650,7 @@ struct TargetProtocolConformanceDescriptor {
   // The conformance, or a generator function for the conformance.
   union {
     /// A direct reference to the witness table for the conformance.
-    RelativeDirectPointer<const WitnessTable> WitnessTable;
+    RelativeDirectPointer<const TargetWitnessTable<Runtime>> WitnessTable;
 
     /// A function that produces the witness table given an instance of the
     /// type.
@@ -2696,7 +2709,7 @@ struct TargetProtocolConformanceDescriptor {
   }
 
   /// Get the directly-referenced static witness table.
-  const swift::WitnessTable *getStaticWitnessTable() const {
+  const swift::TargetWitnessTable<Runtime> *getStaticWitnessTable() const {
     switch (getConformanceKind()) {
     case ConformanceFlags::ConformanceKind::WitnessTable:
       break;
@@ -2727,7 +2740,7 @@ struct TargetProtocolConformanceDescriptor {
   /// Get the witness table for the specified type, realizing it if
   /// necessary, or return null if the conformance does not apply to the
   /// type.
-  const swift::WitnessTable *
+  const swift::TargetWitnessTable<Runtime> *
   getWitnessTable(const TargetMetadata<Runtime> *type) const;
 
 #if !defined(NDEBUG) && SWIFT_OBJC_INTEROP

include/swift/SIL/SILWitnessVisitor.h

@@ -48,6 +48,9 @@ template <class T> class SILWitnessVisitor : public ASTVisitor<T> {
 
 public:
   void visitProtocolDecl(ProtocolDecl *protocol) {
+    // The protocol conformance descriptor gets added first.
+    asDerived().addProtocolConformanceDescriptor();
+
     // Associated types get added after the inherited conformances, but
     // before all the function requirements.
     bool haveAddedAssociatedTypes = false;

lib/IRGen/GenProto.cpp

@@ -746,6 +746,8 @@ namespace {
     SmallVector<WitnessTableEntry, 16> Entries;
 
   public:
+    void addProtocolConformanceDescriptor() { }
+
     /// The next witness is an out-of-line base protocol.
     void addOutOfLineBaseProtocol(ProtocolDecl *baseProto) {
       Entries.push_back(WitnessTableEntry::forOutOfLineBase(baseProto));
@@ -822,7 +824,7 @@ namespace {
     llvm::Value *apply(IRGenFunction &IGF, llvm::Value *wtable) const {
       for (unsigned i = ReversePath.size(); i != 0; --i) {
         wtable = emitInvariantLoadOfOpaqueWitness(IGF, wtable,
-                                                  ReversePath[i-1]);
+                                   ReversePath[i-1].forProtocolWitnessTable());
         wtable = IGF.Builder.CreateBitCast(wtable, IGF.IGM.WitnessTablePtrTy);
       }
       return wtable;
@@ -1224,6 +1226,18 @@ class AccessorConformanceInfo : public ConformanceInfo {
     /// Create the access function.
     void buildAccessFunction(llvm::Constant *wtable);
 
+    /// Add reference to the protocol conformance descriptor that generated
+    /// this table.
+    void addProtocolConformanceDescriptor() {
+      if (Conformance.isBehaviorConformance()) {
+        Table.addNullPointer(IGM.Int8PtrTy);
+      } else {
+        auto descriptor =
+          IGM.getAddrOfProtocolConformanceDescriptor(&Conformance);
+        Table.addBitCast(descriptor, IGM.Int8PtrTy);
+      }
+    }
+
     /// A base protocol is witnessed by a pointer to the conformance
     /// of this type to that protocol.
     void addOutOfLineBaseProtocol(ProtocolDecl *baseProto) {
@@ -1234,7 +1248,8 @@ class AccessorConformanceInfo : public ConformanceInfo {
       assert(entry.getBaseProtocolWitness().Requirement == baseProto
              && "sil witness table does not match protocol");
       auto piIndex = PI.getBaseIndex(baseProto);
-      assert((size_t)piIndex.getValue() == Table.size() &&
+      assert((size_t)piIndex.getValue() ==
+              Table.size() - WitnessTableFirstRequirementOffset &&
              "offset doesn't match ProtocolInfo layout");
 #endif
 
@@ -1279,7 +1294,8 @@ class AccessorConformanceInfo : public ConformanceInfo {
              && "sil witness table does not match protocol");
       auto piIndex =
         PI.getFunctionIndex(cast<AbstractFunctionDecl>(requirement.getDecl()));
-      assert((size_t)piIndex.getValue() == Table.size() &&
+      assert((size_t)piIndex.getValue() ==
+              Table.size() - WitnessTableFirstRequirementOffset &&
              "offset doesn't match ProtocolInfo layout");
 #endif
 
@@ -1310,7 +1326,8 @@ class AccessorConformanceInfo : public ConformanceInfo {
                == requirement.getAssociation()
              && "sil witness table does not match protocol");
       auto piIndex = PI.getAssociatedTypeIndex(requirement);
-      assert((size_t)piIndex.getValue() == Table.size() &&
+      assert((size_t)piIndex.getValue() ==
+              Table.size() - WitnessTableFirstRequirementOffset &&
              "offset doesn't match ProtocolInfo layout");
 #endif
 
@@ -1358,7 +1375,8 @@ class AccessorConformanceInfo : public ConformanceInfo {
                requirement.getAssociatedRequirement()
              && "sil witness table does not match protocol");
       auto piIndex = PI.getAssociatedConformanceIndex(requirement);
-      assert((size_t)piIndex.getValue() == Table.size() &&
+      assert((size_t)piIndex.getValue() ==
+              Table.size() - WitnessTableFirstRequirementOffset &&
              "offset doesn't match ProtocolInfo layout");
 #endif
 
@@ -2057,16 +2075,17 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
 
   // Build the witnesses.
   ConstantInitBuilder builder(*this);
-  auto witnesses = builder.beginArray(Int8PtrTy);
-  WitnessTableBuilder wtableBuilder(*this, witnesses, wt);
+  auto wtableContents = builder.beginArray(Int8PtrTy);
+  WitnessTableBuilder wtableBuilder(*this, wtableContents, wt);
   wtableBuilder.build();
 
-  assert(getProtocolInfo(wt->getConformance()->getProtocol())
-           .getNumWitnesses() == witnesses.size()
+  assert((getProtocolInfo(wt->getConformance()->getProtocol())
+           .getNumWitnesses() + WitnessTableFirstRequirementOffset)
+          == wtableContents.size()
          && "witness table size doesn't match ProtocolInfo");
 
   // Produce the initializer value.
-  auto initializer = witnesses.finishAndCreateFuture();
+  auto initializer = wtableContents.finishAndCreateFuture();
 
   auto global = cast<llvm::GlobalVariable>(
                     getAddrOfWitnessTable(wt->getConformance(), initializer));
@@ -2264,7 +2283,8 @@ emitAssociatedTypeWitnessTableRef(IRGenFunction &IGF,
                                   llvm::Value *wtable,
                                   WitnessIndex index,
                                   llvm::Value *associatedTypeMetadata) {
-  llvm::Value *witness = emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+  llvm::Value *witness = emitInvariantLoadOfOpaqueWitness(IGF, wtable,
+                                             index.forProtocolWitnessTable());
 
   // Cast the witness to the appropriate function type.
   auto sig = IGF.IGM.getAssociatedTypeWitnessTableAccessFunctionSignature();
@@ -2360,7 +2380,8 @@ llvm::Value *MetadataPath::followComponent(IRGenFunction &IGF,
 
     if (source) {
       WitnessIndex index(component.getPrimaryIndex(), /*prefix*/ false);
-      source = emitInvariantLoadOfOpaqueWitness(IGF, source, index);
+      source = emitInvariantLoadOfOpaqueWitness(IGF, source,
+                                              index.forProtocolWitnessTable());
       source = IGF.Builder.CreateBitCast(source, IGF.IGM.WitnessTablePtrTy);
       setProtocolWitnessTableName(IGF.IGM, source, sourceKey.Type,
                                   inheritedProtocol);
@@ -3090,7 +3111,8 @@ irgen::emitWitnessMethodValue(IRGenFunction &IGF,
   auto &fnProtoInfo = IGF.IGM.getProtocolInfo(proto);
   auto index = fnProtoInfo.getFunctionIndex(fn);
   llvm::Value *witnessFnPtr =
-    emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+    emitInvariantLoadOfOpaqueWitness(IGF, wtable,
+                                     index.forProtocolWitnessTable());
 
   auto fnType = IGF.IGM.getSILTypes().getConstantFunctionType(member);
   Signature signature = IGF.IGM.getSignature(fnType);
@@ -3134,7 +3156,8 @@ llvm::Value *irgen::emitAssociatedTypeMetadataRef(IRGenFunction &IGF,
                                                 AssociatedType associatedType) {
   auto &pi = IGF.IGM.getProtocolInfo(associatedType.getSourceProtocol());
   auto index = pi.getAssociatedTypeIndex(associatedType);
-  llvm::Value *witness = emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+  llvm::Value *witness = emitInvariantLoadOfOpaqueWitness(IGF, wtable,
+                                            index.forProtocolWitnessTable());
 
   // Cast the witness to the appropriate function type.
   auto sig = IGF.IGM.getAssociatedTypeMetadataAccessFunctionSignature();

lib/IRGen/LocalTypeData.cpp

@@ -264,7 +264,8 @@ void IRGenFunction::bindLocalTypeDataFromSelfWitnessTable(
                               /*prefix*/ false);
 
           auto table =
-              emitInvariantLoadOfOpaqueWitness(*this, selfTable, wIndex);
+              emitInvariantLoadOfOpaqueWitness(*this, selfTable,
+                                        wIndex.forProtocolWitnessTable());
           table = Builder.CreateBitCast(table, IGM.WitnessTablePtrTy);
           setProtocolWitnessTableName(IGM, table, archetype, proto);
 

lib/IRGen/WitnessIndex.h

@@ -18,6 +18,7 @@
 #ifndef SWIFT_IRGEN_WITNESSINDEX_H
 #define SWIFT_IRGEN_WITNESSINDEX_H
 
+#include "swift/ABI/MetadataValues.h"
 #include "swift/IRGen/ValueWitness.h"
 
 namespace swift {
@@ -38,6 +39,15 @@ class WitnessIndex {
   int getValue() const { return Value; }
 
   bool isPrefix() const { return IsPrefix; }
+
+  /// Adjust the index to refer into a protocol witness table (rather than
+  /// a value witness table).
+  WitnessIndex forProtocolWitnessTable() const {
+    int NewValue = Value < 0
+                     ? Value
+                     : Value + WitnessTableFirstRequirementOffset;
+    return WitnessIndex(NewValue, IsPrefix);
+  }
 };
 
 } // end namespace irgen

lib/SILGen/SILGenType.cpp

@@ -439,6 +439,10 @@ class SILGenConformance : public SILGenWitnessTable<SILGenConformance> {
                                    Entries, ConditionalConformances);
   }
 
+  void addProtocolConformanceDescriptor() {
+  }
+
+
   void addOutOfLineBaseProtocol(ProtocolDecl *baseProtocol) {
     assert(Lowering::TypeConverter::protocolRequiresWitnessTable(baseProtocol));
 
@@ -725,6 +729,8 @@ class SILGenDefaultWitnessTable
     DefaultWitnesses.push_back(SILDefaultWitnessTable::Entry());
   }
 
+  void addProtocolConformanceDescriptor() { }
+
   void addOutOfLineBaseProtocol(ProtocolDecl *baseProto) {
     addMissingDefault();
   }

stdlib/public/runtime/Casting.cpp

@@ -2682,6 +2682,12 @@ namespace {
 
 // protocol _ObjectiveCBridgeable {
 struct _ObjectiveCBridgeableWitnessTable {
+  /// The protocol conformance descriptor.
+  const void *protocolConformanceDescriptor;
+
+  static_assert(WitnessTableFirstRequirementOffset == 1,
+                "Witness table layout changed");
+
   // associatedtype _ObjectiveCType : class
   const Metadata * (*ObjectiveCType)(
                      const Metadata *parentMetadata,

stdlib/public/runtime/Metadata.cpp

@@ -2749,7 +2749,8 @@ static bool doesNotRequireInstantiation(GenericWitnessTable *genericTable) {
   if (genericTable->Instantiator.isNull() &&
       genericTable->WitnessTablePrivateSizeInWords == 0 &&
       genericTable->WitnessTableSizeInWords ==
-        genericTable->Protocol->NumRequirements) {
+        (genericTable->Protocol->NumRequirements +
+           WitnessTableFirstRequirementOffset)) {
     return true;
   }
 
@@ -2770,11 +2771,13 @@ allocateWitnessTable(GenericWitnessTable *genericTable,
 
   // The number of mandatory requirements, i.e. requirements lacking
   // default implementations.
-  size_t numMandatoryRequirements = protocol->NumMandatoryRequirements;
+  size_t numMandatoryRequirements =
+    protocol->NumMandatoryRequirements + WitnessTableFirstRequirementOffset;
   assert(numPatternWitnesses >= numMandatoryRequirements);
 
   // The total number of requirements.
-  size_t numRequirements = protocol->NumRequirements;
+  size_t numRequirements =
+    protocol->NumRequirements + WitnessTableFirstRequirementOffset;
   assert(numPatternWitnesses <= numRequirements);
 
   // Number of bytes for any private storage used by the conformance itself.
@@ -2807,7 +2810,9 @@ allocateWitnessTable(GenericWitnessTable *genericTable,
 
   // Fill in any default requirements.
   for (size_t i = numPatternWitnesses, e = numRequirements; i < e; ++i) {
-    void *defaultImpl = requirements[i].DefaultImplementation.get();
+    size_t requirementIndex = i - WitnessTableFirstRequirementOffset;
+    void *defaultImpl =
+      requirements[requirementIndex].DefaultImplementation.get();
     assert(defaultImpl &&
            "no default implementation for missing requirement");
     table[i] = defaultImpl;