SE-0492: Metatypes and existential metatypes

SwiftCompilerSources/Sources/AST/Conformance.swift

@@ -87,6 +87,23 @@ public struct Conformance: CustomStringConvertible, Hashable, NoReflectionChildr
     assert(isConcrete)
     return bridged.getAssociatedConformance(assocType.bridged, proto.bridged).conformance
   }
+
+  // This is a less precise definition of "resilient conformance" because it's
+  // only used for SIL optimizations -- where it's okay to think a conformance
+  // is resilient even if IRGen will decide it's not (see
+  // IRGenModule::isResilientConformance).
+  public func isResilientConformance(currentModule: ModuleDecl) -> Bool {
+    let conformanceModule = self.protocol.parentModule
+    let protocolModule = self.protocol.parentModule
+
+    // If the protocol and the conformance are both in the current module,
+    // they're not resilient.
+    if conformanceModule == currentModule && protocolModule == currentModule {
+      return false
+    }
+
+    return true
+  }
 }
 
 public struct ConformanceArray : RandomAccessCollection, CustomReflectable {

SwiftCompilerSources/Sources/AST/Declarations.swift

@@ -76,6 +76,8 @@ final public class ClassDecl: NominalTypeDecl {
 
 final public class ProtocolDecl: NominalTypeDecl {
   public var requiresClass: Bool { bridged.ProtocolDecl_requiresClass() }
+
+  public var isInvertible: Bool { bridged.ProtocolDecl_isInvertible() }
 }
 
 final public class BuiltinTupleDecl: NominalTypeDecl {}

SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift

@@ -462,6 +462,27 @@ extension Instruction {
       }
     case let gvi as GlobalValueInst:
       return context.canMakeStaticObjectReadOnly(objectType: gvi.type)
+
+    // Metatypes (and upcasts of them to existentials) can be used as static initializers for SE-0492, as long as they
+    // do not require an accessor to reference the metadata (i.e. are not generic, not resilient and not a class).
+    // See also irgen::isCanonicalCompleteTypeMetadataStaticallyAddressable.
+    case let mti as MetatypeInst:
+      let silType = mti.type.loweredInstanceTypeOfMetatype(in: parentFunction)
+      let instanceType = mti.type.canonicalType.instanceTypeOfMetatype
+      if !mti.type.isGenericAtAnyLevel,
+        !instanceType.isClass,
+        let nominal = instanceType.nominal,
+        !nominal.isGenericAtAnyLevel,
+        silType.isFixedABI(in: mti.parentFunction) {
+        return true
+      }
+      return false
+    case let iemi as InitExistentialMetatypeInst:
+      let isAnyConformanceResilient = iemi.conformances.contains { 
+        !$0.protocol.isInvertible && $0.isResilientConformance(currentModule: context.currentModuleContext)
+      }
+      return !iemi.type.isGenericAtAnyLevel && !isAnyConformanceResilient
+
     case is StructInst,
          is TupleInst,
          is EnumInst,

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -901,6 +901,10 @@ class OpenExistentialBoxValueInst : SingleValueInstruction, UnaryInstruction {}
 final public
 class InitExistentialMetatypeInst : SingleValueInstruction, UnaryInstruction {
   public var metatype: Value { operand.value }
+
+  public var conformances: ConformanceArray {
+    ConformanceArray(bridged: bridged.InitExistentialMetatypeInst_getConformances())
+  }
 }
 
 final public

SwiftCompilerSources/Sources/SIL/Type.swift

@@ -103,6 +103,10 @@ public struct Type : TypeProperties, CustomStringConvertible, NoReflectionChildr
     bridged.isAddressableForDeps(function.bridged)
   }
 
+  public func isFixedABI(in function: Function) -> Bool {
+    bridged.isFixedABI(function.bridged)
+  }
+
   /// If this is a raw layout type, returns the substituted like-type.
   public var rawLayoutSubstitutedLikeType: AST.`Type`? {
     .init(bridgedOrNil: bridged.getRawLayoutSubstitutedLikeType())

include/swift/AST/ASTBridging.h

@@ -335,6 +335,7 @@ struct BridgedDeclObj {
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedASTType Class_getSuperclass() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedDeclObj Class_getDestructor() const;
   BRIDGED_INLINE bool ProtocolDecl_requiresClass() const;
+  BRIDGED_INLINE bool ProtocolDecl_isInvertible() const;
   BRIDGED_INLINE bool AbstractFunction_isOverridden() const;
   BRIDGED_INLINE bool Destructor_isIsolated() const;
   BRIDGED_INLINE bool EnumElementDecl_hasAssociatedValues() const;

include/swift/AST/ASTBridgingImpl.h

@@ -222,6 +222,10 @@ bool BridgedDeclObj::ProtocolDecl_requiresClass() const {
   return getAs<swift::ProtocolDecl>()->requiresClass();
 }
 
+bool BridgedDeclObj::ProtocolDecl_isInvertible() const {
+  return getAs<swift::ProtocolDecl>()->getInvertibleProtocolKind() != std::nullopt;
+}
+
 bool BridgedDeclObj::AbstractFunction_isOverridden() const {
   return getAs<swift::AbstractFunctionDecl>()->isOverridden();
 }

include/swift/SIL/SILBridging.h

@@ -290,6 +290,7 @@ struct BridgedType {
   BRIDGED_INLINE bool isExactSuperclassOf(BridgedType t) const;
   BRIDGED_INLINE bool isMarkedAsImmortal() const;
   BRIDGED_INLINE bool isAddressableForDeps(BridgedFunction f) const;
+  BRIDGED_INLINE bool isFixedABI(BridgedFunction f) const;
   BRIDGED_INLINE SWIFT_IMPORT_UNSAFE BridgedASTType getRawLayoutSubstitutedLikeType() const;
   BRIDGED_INLINE SWIFT_IMPORT_UNSAFE BridgedASTType getRawLayoutSubstitutedCountType() const;
   BRIDGED_INLINE bool mayHaveCustomDeinit(BridgedFunction f) const;
@@ -797,6 +798,7 @@ struct BridgedInstruction {
   BRIDGED_INLINE bool IndexAddrInst_needsStackProtection() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedConformanceArray InitExistentialRefInst_getConformances() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedCanType InitExistentialRefInst_getFormalConcreteType() const;
+  SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedConformanceArray InitExistentialMetatypeInst_getConformances() const;
   BRIDGED_INLINE bool OpenExistentialAddr_isImmutable() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedGlobalVar GlobalAccessInst_getGlobal() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedGlobalVar AllocGlobalInst_getGlobal() const;

include/swift/SIL/SILBridgingImpl.h

@@ -398,6 +398,10 @@ bool BridgedType::isAddressableForDeps(BridgedFunction f) const {
   return unbridged().isAddressableForDeps(*f.getFunction());
 }
 
+bool BridgedType::isFixedABI(BridgedFunction f) const {
+  return unbridged().isFixedABI(*f.getFunction());
+}
+
 BridgedASTType BridgedType::getRawLayoutSubstitutedLikeType() const {
   return {unbridged().getRawLayoutSubstitutedLikeType().getPointer()};
 }
@@ -1249,6 +1253,10 @@ BridgedCanType BridgedInstruction::InitExistentialRefInst_getFormalConcreteType(
   return getAs<swift::InitExistentialRefInst>()->getFormalConcreteType();
 }
 
+BridgedConformanceArray BridgedInstruction::InitExistentialMetatypeInst_getConformances() const {
+  return {getAs<swift::InitExistentialMetatypeInst>()->getConformances()};
+}
+
 bool BridgedInstruction::OpenExistentialAddr_isImmutable() const {
   switch (getAs<swift::OpenExistentialAddrInst>()->getAccessKind()) {
     case swift::OpenedExistentialAccess::Immutable: return true;

include/swift/SIL/SILBuilder.h

@@ -2155,6 +2155,11 @@ class SILBuilder {
   createInitExistentialMetatype(SILLocation Loc, SILValue metatype,
                                 SILType existentialType,
                                 ArrayRef<ProtocolConformanceRef> conformances) {
+    if (isInsertingIntoGlobal()) {
+      return insert(InitExistentialMetatypeInst::create(
+          getSILDebugLocation(Loc), existentialType, metatype, conformances,
+            getModule()));
+    }
     return insert(InitExistentialMetatypeInst::create(
         getSILDebugLocation(Loc), existentialType, metatype, conformances,
         &getFunction()));
@@ -2289,6 +2294,10 @@ class SILBuilder {
   }
 
   MetatypeInst *createMetatype(SILLocation Loc, SILType Metatype) {
+    if (isInsertingIntoGlobal()) {
+      return insert(MetatypeInst::create(getSILDebugLocation(Loc), Metatype,
+                                         getModule()));
+    }
     return insert(MetatypeInst::create(getSILDebugLocation(Loc), Metatype,
                                        &getFunction()));
   }

include/swift/SIL/SILInstruction.h

@@ -7464,6 +7464,9 @@ class MetatypeInst final
                ArrayRef<SILValue> TypeDependentOperands)
     : NullaryInstructionWithTypeDependentOperandsBase(DebugLoc,
                                           TypeDependentOperands, Metatype) {}
+
+  static MetatypeInst *create(SILDebugLocation DebugLoc, SILType Metatype,
+                              SILModule &Mod);
 
   static MetatypeInst *create(SILDebugLocation DebugLoc, SILType Metatype,
                               SILFunction *F);
@@ -8141,6 +8144,11 @@ class InitExistentialMetatypeInst final
                               ArrayRef<SILValue> TypeDependentOperands,
                               ArrayRef<ProtocolConformanceRef> conformances);
 
+  static InitExistentialMetatypeInst *
+  create(SILDebugLocation DebugLoc, SILType existentialMetatypeType,
+         SILValue metatype, ArrayRef<ProtocolConformanceRef> conformances,
+         SILModule &mod);
+
   static InitExistentialMetatypeInst *
   create(SILDebugLocation DebugLoc, SILType existentialMetatypeType,
          SILValue metatype, ArrayRef<ProtocolConformanceRef> conformances,

lib/IRGen/GenConstant.cpp

@@ -20,9 +20,11 @@
 #include "Explosion.h"
 #include "GenConstant.h"
 #include "GenEnum.h"
+#include "GenExistential.h"
 #include "GenIntegerLiteral.h"
 #include "GenStruct.h"
 #include "GenTuple.h"
+#include "MetadataRequest.h"
 #include "TypeInfo.h"
 #include "StructLayout.h"
 #include "Callee.h"
@@ -31,9 +33,11 @@
 #include "swift/IRGen/Linking.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/Range.h"
+#include "swift/SIL/SILInstruction.h"
 #include "swift/SIL/SILModule.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Support/BLAKE3.h"
+#include "llvm/Support/ErrorHandling.h"
 
 using namespace swift;
 using namespace irgen;
@@ -414,6 +418,26 @@ Explosion irgen::emitConstantValue(IRGenModule &IGM, SILValue operand,
     assert(ti.isFixedSize(expansion));
     Address addr = IGM.getAddrOfSILGlobalVariable(var, ti, NotForDefinition);
     return addr.getAddress();
+  } else if (auto *mti = dyn_cast<MetatypeInst>(operand)) {
+    auto metaTy = mti->getType().castTo<MetatypeType>();
+    auto type = metaTy.getInstanceType();
+    ASSERT(isCanonicalCompleteTypeMetadataStaticallyAddressable(IGM, type));
+    return IGM.getAddrOfTypeMetadata(type);
+  } else if (auto *iemi = dyn_cast<InitExistentialMetatypeInst>(operand)) {
+    auto *mti =
+        dyn_cast<MetatypeInst>(iemi->getOperand().getDefiningInstruction());
+    ASSERT(mti != nullptr && "couldn't constant fold initializer expression");
+
+    auto metaTy = mti->getType().castTo<MetatypeType>();
+    auto type = metaTy.getInstanceType();
+    ASSERT(isCanonicalCompleteTypeMetadataStaticallyAddressable(IGM, type));
+    llvm::Constant *metadata = IGM.getAddrOfTypeMetadata(type);
+
+    Explosion result;
+    emitExistentialMetatypeContainer(IGM, result, iemi->getType(), metadata,
+                                     iemi->getOperand()->getType(),
+                                     iemi->getConformances());
+    return result;
   } else if (auto *atp = dyn_cast<AddressToPointerInst>(operand)) {
     auto *val = emitConstantValue(IGM, atp->getOperand()).claimNextConstant();
     return val;

lib/IRGen/GenDecl.cpp

@@ -25,11 +25,13 @@
 #include "swift/AST/ModuleDependencies.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/Pattern.h"
+#include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/TypeMemberVisitor.h"
 #include "swift/AST/Types.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/Mangler.h"
+#include "swift/Basic/PrettyStackTrace.h"
 #include "swift/ClangImporter/ClangModule.h"
 #include "swift/Demangling/ManglingMacros.h"
 #include "swift/IRGen/Linking.h"
@@ -2931,6 +2933,9 @@ Address IRGenModule::getAddrOfSILGlobalVariable(SILGlobalVariable *var,
 llvm::Constant *IRGenModule::getGlobalInitValue(SILGlobalVariable *var,
                                                 llvm::Type *storageType,
                                                 Alignment alignment) {
+  PrettyStackTraceStringAction trace(
+      "constant-folding init value for SIL global", var->getName());
+
   if (var->isInitializedObject()) {
     StructLayout *layout = StaticObjectLayouts[var].layout.get();
     ObjectInst *oi = cast<ObjectInst>(var->getStaticInitializerValue());

lib/IRGen/GenExistential.cpp

@@ -2033,6 +2033,40 @@ void irgen::emitExistentialMetatypeContainer(IRGenFunction &IGF,
                               });
 }
 
+/// Emit an existential metatype container from a metatype value as an
+/// explosion of llvm::Constant values (suitable for static initialization).
+void irgen::emitExistentialMetatypeContainer(
+    IRGenModule &IGM, Explosion &out, SILType outType, llvm::Constant *metatype,
+    SILType metatypeType, ArrayRef<ProtocolConformanceRef> conformances) {
+  assert(outType.is<ExistentialMetatypeType>());
+  auto &destTI = IGM.getTypeInfo(outType).as<ExistentialMetatypeTypeInfo>();
+  out.add(metatype);
+
+  auto srcType = metatypeType.castTo<MetatypeType>().getInstanceType();
+  auto destType = outType.castTo<ExistentialMetatypeType>().getInstanceType();
+  while (auto destMetatypeType = dyn_cast<ExistentialMetatypeType>(destType)) {
+    destType = destMetatypeType.getInstanceType();
+    srcType = cast<AnyMetatypeType>(srcType).getInstanceType();
+  }
+
+  // Emit the witness table pointers as constants.
+  for (auto protocol : destTI.getStoredProtocols()) {
+    // Find the corresponding conformance
+    ProtocolConformanceRef conformance;
+    for (auto conf : conformances) {
+      if (conf.getProtocol() == protocol) {
+        conformance = conf;
+        break;
+      }
+    }
+    assert(conformance.isConcrete() && "missing conformance");
+
+    // Emit witness table constant
+    auto table = IGM.getAddrOfWitnessTable(conformance.getConcrete());
+    out.add(table);
+  }
+}
+
 void irgen::emitMetatypeOfOpaqueExistential(IRGenFunction &IGF, Address buffer,
                                             SILType type, Explosion &out) {
   assert(type.isExistentialType());

lib/IRGen/GenExistential.h

@@ -34,6 +34,7 @@ namespace irgen {
   class Address;
   class Explosion;
   class IRGenFunction;
+  class IRGenModule;
 
   /// Emit the metadata and witness table initialization for an allocated
   /// opaque existential container.
@@ -44,16 +45,20 @@ namespace irgen {
                                    SILType loweredSrcType,
                                  ArrayRef<ProtocolConformanceRef> conformances);
 
-  /// Emit an existential metatype container from a metatype value
-  /// as an explosion.
-  void emitExistentialMetatypeContainer(IRGenFunction &IGF,
-                                        Explosion &out,
-                                        SILType outType,
-                                        llvm::Value *metatype,
-                                        SILType metatypeType,
-                                 ArrayRef<ProtocolConformanceRef> conformances);
-
-
+  /// Emit an existential metatype container from a metatype value as an
+  /// explosion.
+  void emitExistentialMetatypeContainer(
+      IRGenFunction &IGF, Explosion &out, SILType outType,
+      llvm::Value *metatype, SILType metatypeType,
+      ArrayRef<ProtocolConformanceRef> conformances);
+
+  /// Emit an existential metatype container from a metatype value as an
+  /// explosion of llvm::Constant values (suitable for static initialization).
+  void emitExistentialMetatypeContainer(
+      IRGenModule &IGM, Explosion &out, SILType outType,
+      llvm::Constant *metatype, SILType metatypeType,
+      ArrayRef<ProtocolConformanceRef> conformances);
+
   /// Emit a class existential container from a class instance value
   /// as an explosion.
   void emitClassExistentialContainer(IRGenFunction &IGF,

lib/SIL/IR/SILInstructions.cpp

@@ -2327,6 +2327,17 @@ InitExistentialMetatypeInst::InitExistentialMetatypeInst(
                           getTrailingObjects<ProtocolConformanceRef>());
 }
 
+InitExistentialMetatypeInst *InitExistentialMetatypeInst::create(
+    SILDebugLocation Loc, SILType existentialMetatypeType, SILValue metatype,
+    ArrayRef<ProtocolConformanceRef> conformances, SILModule &M) {
+  unsigned size = totalSizeToAlloc<swift::Operand, ProtocolConformanceRef>(
+      1, conformances.size());
+  void *buffer = M.allocateInst(size, alignof(InitExistentialMetatypeInst));
+  return ::new (buffer) InitExistentialMetatypeInst(
+      Loc, existentialMetatypeType, metatype,
+      {}, conformances);
+}
+
 InitExistentialMetatypeInst *InitExistentialMetatypeInst::create(
     SILDebugLocation Loc, SILType existentialMetatypeType, SILValue metatype,
     ArrayRef<ProtocolConformanceRef> conformances, SILFunction *F) {
@@ -2737,6 +2748,13 @@ CheckedCastBranchInst *CheckedCastBranchInst::create(
       Target2Count, forwardingOwnershipKind, preservesOwnership);
 }
 
+MetatypeInst *MetatypeInst::create(SILDebugLocation Loc, SILType Ty,
+                                   SILModule &Mod) {
+  auto Size = totalSizeToAlloc<swift::Operand>(1);
+  auto Buffer = Mod.allocateInst(Size, alignof(MetatypeInst));
+  return ::new (Buffer) MetatypeInst(Loc, Ty, {});
+}
+
 MetatypeInst *MetatypeInst::create(SILDebugLocation Loc, SILType Ty,
                                    SILFunction *F) {
   SILModule &Mod = F->getModule();