Package CMO containing the following PRs.

#74531
#74468
#74416
#74070
#73902
#73754
#73717
#72606
#73566
#73478
#73686
#72937
#73708
#73751
#73794

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyLoad.swift

@@ -281,7 +281,7 @@ private func transitivelyErase(load: LoadInst, _ context: SimplifyContext) {
 
 private extension Value {
   func canBeCopied(into function: Function, _ context: SimplifyContext) -> Bool {
-    if !function.isSerialized {
+    if !function.isAnySerialized {
       return true
     }
 
@@ -297,7 +297,7 @@ private extension Value {
 
     while let value = worklist.pop() {
       if let fri = value as? FunctionRefInst {
-        if !fri.referencedFunction.hasValidLinkageForFragileRef {
+        if !fri.referencedFunction.hasValidLinkageForFragileRef(function.serializedKind) {
           return false
         }
       }

SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift

@@ -549,9 +549,8 @@ extension FullApplySite {
       return false
     }
     // Cannot inline a non-inlinable function it an inlinable function.
-    if parentFunction.isSerialized,
-       let calleeFunction = referencedFunction,
-       !calleeFunction.isSerialized {
+    if let calleeFunction = referencedFunction,
+       !calleeFunction.canBeInlinedIntoCaller(parentFunction.serializedKind) {
       return false
     }
 

SwiftCompilerSources/Sources/SIL/Function.swift

@@ -122,7 +122,37 @@ final public class Function : CustomStringConvertible, HasShortDescription, Hash
   }
   public var isSerialized: Bool { bridged.isSerialized() }
 
-  public var hasValidLinkageForFragileRef: Bool { bridged.hasValidLinkageForFragileRef() }
+  public var isAnySerialized: Bool { bridged.isAnySerialized() }
+
+  public enum SerializedKind {
+    case notSerialized, serialized, serializedForPackage
+  }
+
+  public var serializedKind: SerializedKind {
+    switch bridged.getSerializedKind() {
+    case .IsNotSerialized: return .notSerialized
+    case .IsSerialized: return .serialized
+    case .IsSerializedForPackage: return .serializedForPackage
+    default: fatalError()
+    }
+  }
+
+  private func serializedKindBridged(_ arg: SerializedKind) -> BridgedFunction.SerializedKind {
+    switch arg {
+    case .notSerialized: return .IsNotSerialized
+    case .serialized: return .IsSerialized
+    case .serializedForPackage: return .IsSerializedForPackage
+    default: fatalError()
+    }
+  }
+
+  public func canBeInlinedIntoCaller(_ kind: SerializedKind) -> Bool {
+    bridged.canBeInlinedIntoCaller(serializedKindBridged(kind))
+  }
+
+  public func hasValidLinkageForFragileRef(_ kind: SerializedKind) -> Bool {
+    bridged.hasValidLinkageForFragileRef(serializedKindBridged(kind))
+  }
 
   public enum ThunkKind {
     case noThunk, thunk, reabstractionThunk, signatureOptimizedThunk

include/swift/AST/Decl.h

@@ -697,7 +697,7 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
     HasAnyUnavailableDuringLoweringValues : 1
   );
 
-  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1,
+  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1,
     /// If the module is compiled as static library.
     StaticLibrary : 1,
 
@@ -756,7 +756,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
     HasCxxInteroperability : 1,
 
     /// Whether this module has been built with -experimental-allow-non-resilient-access.
-    AllowNonResilientAccess : 1
+    AllowNonResilientAccess : 1,
+
+    /// Whether this module has been built with -experimental-package-cmo.
+    SerializePackageEnabled : 1
   );
 
   SWIFT_INLINE_BITFIELD(PrecedenceGroupDecl, Decl, 1+2,
@@ -4148,6 +4151,13 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   /// is built resiliently.
   bool isResilient() const;
 
+  /// True if the decl is resilient AND also its defining module does
+  /// _not_ allow non-resilient access; the module can allow such access
+  /// if package optimization is enabled so its client modules within the
+  /// same package can have a direct access to this decl even if it's
+  /// resilient.
+  bool isStrictlyResilient() const;
+
   /// Returns whether this decl is accessed non/resiliently at the _use_ site
   /// in \p accessingModule, depending on \p expansion.
   ///
@@ -5966,6 +5976,13 @@ class AbstractStorageDecl : public ValueDecl {
   /// property from the given module?
   bool isResilient(ModuleDecl *M, ResilienceExpansion expansion) const;
 
+  /// True if the decl is resilient AND also its defining module does
+  /// _not_ allow non-resilient access; the module can allow such access
+  /// if package optimization is enabled so its client modules within the
+  /// same package can have a direct access to this decl even if it's
+  /// resilient.
+  bool isStrictlyResilient() const;
+
   /// True if the storage can be referenced by a keypath directly.
   /// Otherwise, its override must be referenced.
   bool isValidKeyPathComponent() const;

include/swift/AST/Module.h

@@ -736,6 +736,16 @@ class ModuleDecl
     Bits.ModuleDecl.AllowNonResilientAccess = flag;
   }
 
+  /// Returns true if -experimental-package-cmo was passed, which
+  /// enables serialization of package, public, and inlinable decls in a
+  /// package. This requires -experimental-allow-non-resilient-access.
+  bool serializePackageEnabled() const {
+    return Bits.ModuleDecl.SerializePackageEnabled;
+  }
+  void setSerializePackageEnabled(bool flag = true) {
+    Bits.ModuleDecl.SerializePackageEnabled = flag;
+  }
+
   /// Returns true if this module is a non-Swift module that was imported into
   /// Swift.
   ///
@@ -783,6 +793,15 @@ class ModuleDecl
     return getResilienceStrategy() != ResilienceStrategy::Default;
   }
 
+  /// True if this module is resilient AND also does _not_ allow
+  /// non-resilient access; the module can allow such access if
+  /// package optimization is enabled so its client modules within
+  /// the same package can have a direct access to decls in this
+  /// module even if it's built resiliently.
+  bool isStrictlyResilient() const {
+    return isResilient() && !allowNonResilientAccess();
+  }
+
   /// Look up a (possibly overloaded) value set at top-level scope
   /// (but with the specified access path, which may come from an import decl)
   /// within the current module.

include/swift/AST/Types.h

@@ -6618,6 +6618,8 @@ enum class OpaqueSubstitutionKind {
   // Can be done if the underlying type is accessible from the context we
   // substitute into. Private types cannot be accessed from a different TU.
   SubstituteSameModuleMaximalResilience,
+  // Same as previous but with package and above visibility.
+  SubstituteSamePackageMaximalResilience,
   // Substitute in a different module from the opaque defining decl. Can only
   // be done if the underlying type is public.
   SubstituteNonResilientModule

include/swift/SIL/GenericSpecializationMangler.h

@@ -37,7 +37,7 @@ class SpecializationMangler : public Mangle::ASTMangler {
   /// The specialization pass.
   SpecializationPass Pass;
 
-  IsSerialized_t Serialized;
+  swift::SerializedKind_t Serialized;
 
   /// The original function which is specialized.
   SILFunction *Function;
@@ -50,12 +50,12 @@ class SpecializationMangler : public Mangle::ASTMangler {
   PossibleEffects RemovedEffects;
 
 protected:
-  SpecializationMangler(SpecializationPass P, IsSerialized_t Serialized,
+  SpecializationMangler(SpecializationPass P, swift::SerializedKind_t Serialized,
                         SILFunction *F)
       : Pass(P), Serialized(Serialized), Function(F),
         ArgOpBuffer(ArgOpStorage) {}
 
-  SpecializationMangler(SpecializationPass P, IsSerialized_t Serialized,
+  SpecializationMangler(SpecializationPass P, swift::SerializedKind_t Serialized,
                         std::string functionName)
       : Pass(P), Serialized(Serialized), Function(nullptr),
         FunctionName(functionName), ArgOpBuffer(ArgOpStorage) {}
@@ -88,7 +88,7 @@ class GenericSpecializationMangler : public SpecializationMangler {
                                       SubstitutionMap subs);
 
 public:
-  GenericSpecializationMangler(SILFunction *F, IsSerialized_t Serialized)
+  GenericSpecializationMangler(SILFunction *F, swift::SerializedKind_t Serialized)
       : SpecializationMangler(SpecializationPass::GenericSpecializer,
                               Serialized, F) {}
 

include/swift/SIL/SILBridging.h

@@ -529,6 +529,12 @@ struct BridgedFunction {
     IsSignatureOptimizedThunk
   };
 
+  enum class SerializedKind {
+    IsNotSerialized,
+    IsSerialized,
+    IsSerializedForPackage
+  };
+
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE swift::SILFunction * _Nonnull getFunction() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedStringRef getName() const;
   SWIFT_IMPORT_UNSAFE BridgedOwnedString getDebugDescription() const;
@@ -558,7 +564,10 @@ struct BridgedFunction {
   BRIDGED_INLINE PerformanceConstraints getPerformanceConstraints() const;
   BRIDGED_INLINE InlineStrategy getInlineStrategy() const;
   BRIDGED_INLINE bool isSerialized() const;
-  BRIDGED_INLINE bool hasValidLinkageForFragileRef() const;
+  BRIDGED_INLINE bool isAnySerialized() const;
+  BRIDGED_INLINE SerializedKind getSerializedKind() const;
+  BRIDGED_INLINE bool canBeInlinedIntoCaller(SerializedKind) const;
+  BRIDGED_INLINE bool hasValidLinkageForFragileRef(SerializedKind) const;
   BRIDGED_INLINE ThunkKind isThunk() const;
   BRIDGED_INLINE void setThunk(ThunkKind) const;
   BRIDGED_INLINE bool needsStackProtection() const;

include/swift/SIL/SILBridgingImpl.h

@@ -690,8 +690,20 @@ bool BridgedFunction::isSerialized() const {
   return getFunction()->isSerialized();
 }
 
-bool BridgedFunction::hasValidLinkageForFragileRef() const {
-  return getFunction()->hasValidLinkageForFragileRef();
+bool BridgedFunction::isAnySerialized() const {
+  return getFunction()->isAnySerialized();
+}
+
+BridgedFunction::SerializedKind BridgedFunction::getSerializedKind() const {
+  return (SerializedKind)getFunction()->getSerializedKind();
+}
+
+bool BridgedFunction::canBeInlinedIntoCaller(SerializedKind kind) const {
+  return getFunction()->canBeInlinedIntoCaller(swift::SerializedKind_t(kind));
+}
+
+bool BridgedFunction::hasValidLinkageForFragileRef(SerializedKind kind) const {
+  return getFunction()->hasValidLinkageForFragileRef(swift::SerializedKind_t(kind));
 }
 
 bool BridgedFunction::needsStackProtection() const {

include/swift/SIL/SILDeclRef.h

@@ -46,7 +46,7 @@ namespace swift {
   class EffectsAttr;
   class FileUnit;
   class SILFunctionType;
-  enum IsSerialized_t : unsigned char;
+  enum SerializedKind_t : uint8_t;
   enum class SubclassScope : unsigned char;
   class SILModule;
   class SILLocation;
@@ -384,7 +384,11 @@ struct SILDeclRef {
   /// True if the function should be treated as transparent.
   bool isTransparent() const;
   /// True if the function should have its body serialized.
-  IsSerialized_t isSerialized() const;
+  bool isSerialized() const;
+  /// True if this function is neither [serialized] or [serialized_for_package].
+  bool isNotSerialized() const;
+  /// Returns IsNotSerialized, IsSerializedForPackage, or IsSerialized.
+  SerializedKind_t getSerializedKind() const;
   /// True if the function has noinline attribute.
   bool isNoinline() const;
   /// True if the function has __always inline attribute.

include/swift/SIL/SILFunction.h

@@ -362,7 +362,7 @@ class SILFunction
   unsigned Transparent : 1;
 
   /// The function's serialized attribute.
-  bool Serialized : 1;
+  unsigned SerializedKind : 2;
 
   /// Specifies if this function is a thunk or a reabstraction thunk.
   ///
@@ -502,7 +502,7 @@ class SILFunction
   SILFunction(SILModule &module, SILLinkage linkage, StringRef mangledName,
               CanSILFunctionType loweredType, GenericEnvironment *genericEnv,
               IsBare_t isBareSILFunction, IsTransparent_t isTrans,
-              IsSerialized_t isSerialized, ProfileCounter entryCount,
+              SerializedKind_t serializedKind, ProfileCounter entryCount,
               IsThunk_t isThunk, SubclassScope classSubclassScope,
               Inline_t inlineStrategy, EffectsKind E,
               const SILDebugScope *debugScope,
@@ -515,7 +515,7 @@ class SILFunction
   create(SILModule &M, SILLinkage linkage, StringRef name,
          CanSILFunctionType loweredType, GenericEnvironment *genericEnv,
          std::optional<SILLocation> loc, IsBare_t isBareSILFunction,
-         IsTransparent_t isTrans, IsSerialized_t isSerialized,
+         IsTransparent_t isTrans, SerializedKind_t serializedKind,
          ProfileCounter entryCount, IsDynamicallyReplaceable_t isDynamic,
          IsDistributed_t isDistributed,
          IsRuntimeAccessible_t isRuntimeAccessible,
@@ -528,7 +528,7 @@ class SILFunction
 
   void init(SILLinkage Linkage, StringRef Name, CanSILFunctionType LoweredType,
             GenericEnvironment *genericEnv, IsBare_t isBareSILFunction,
-            IsTransparent_t isTrans, IsSerialized_t isSerialized,
+            IsTransparent_t isTrans, SerializedKind_t serializedKind,
             ProfileCounter entryCount, IsThunk_t isThunk,
             SubclassScope classSubclassScope, Inline_t inlineStrategy,
             EffectsKind E, const SILDebugScope *DebugScope,
@@ -780,11 +780,7 @@ class SILFunction
     return getLoweredFunctionType()->getRepresentation();
   }
 
-  ResilienceExpansion getResilienceExpansion() const {
-    return (isSerialized()
-            ? ResilienceExpansion::Minimal
-            : ResilienceExpansion::Maximal);
-  }
+  ResilienceExpansion getResilienceExpansion() const;
 
   // Returns the type expansion context to be used inside this function.
   TypeExpansionContext getTypeExpansionContext() const {
@@ -875,13 +871,32 @@ class SILFunction
   /// Set the function's linkage attribute.
   void setLinkage(SILLinkage linkage) { Linkage = unsigned(linkage); }
 
-  /// Returns true if this function can be inlined into a fragile function
-  /// body.
-  bool hasValidLinkageForFragileInline() const { return isSerialized(); }
+///   Checks if this (callee) function body can be inlined into the caller
+///   by comparing their `SerializedKind_t` values.
+///
+///   If both callee and caller are `not_serialized`, the callee can be inlined
+///   into the caller during SIL inlining passes even if it (and the caller)
+///   might contain private symbols. If this callee is `serialized_for_pkg`,
+///   it can only be referenced by a serialized caller but not inlined into
+///   it.
+///
+///  ```
+///   canInlineInto:                                 Caller
+///                              | not_serialized | serialized_for_pkg | serialized
+///          not_serialized      |      ok        |       no           |    no
+///  Callee  serialized_for_pkg  |      ok        |       ok           |    no
+///          serialized          |      ok        |       ok           |    ok
+///
+///  ```
+///
+/// \p callerSerializedKind The caller's SerializedKind.
+  bool canBeInlinedIntoCaller(SerializedKind_t callerSerializedKind) const;
 
   /// Returns true if this function can be referenced from a fragile function
   /// body.
-  bool hasValidLinkageForFragileRef() const;
+  /// \p callerSerializedKind The caller's SerializedKind. Used to be passed to
+  ///                         \c canBeInlinedIntoCaller.
+  bool hasValidLinkageForFragileRef(SerializedKind_t callerSerializedKind) const;
 
   /// Get's the effective linkage which is used to derive the llvm linkage.
   /// Usually this is the same as getLinkage(), except in one case: if this
@@ -1135,11 +1150,21 @@ class SILFunction
     assert(!Transparent || !IsDynamicReplaceable);
   }
 
+  bool isSerialized() const {
+    return SerializedKind_t(SerializedKind) == IsSerialized;
+  }
+  bool isAnySerialized() const {
+    return SerializedKind_t(SerializedKind) == IsSerialized ||
+           SerializedKind_t(SerializedKind) == IsSerializedForPackage;
+  }
+
   /// Get this function's serialized attribute.
-  IsSerialized_t isSerialized() const { return IsSerialized_t(Serialized); }
-  void setSerialized(IsSerialized_t isSerialized) {
-    Serialized = isSerialized;
-    assert(this->isSerialized() == isSerialized &&
+  SerializedKind_t getSerializedKind() const {
+    return SerializedKind_t(SerializedKind);
+  }
+  void setSerializedKind(SerializedKind_t serializedKind) {
+    SerializedKind = serializedKind;
+    assert(this->getSerializedKind() == serializedKind &&
            "too few bits for Serialized storage");
   }