[AST] Sink ModuleDecl's flags down into the shared Decl bitfields (#20051)

Saves 4 bytes per ModuleDecl. No functionality change.

Author: jrose-apple

include/swift/AST/Decl.h

@@ -463,7 +463,8 @@ class alignas(1 << DeclAlignInBits) Decl {
     HasStubImplementation : 1
   );
 
-  SWIFT_INLINE_BITFIELD_EMPTY(AbstractTypeParamDecl, ValueDecl);
+  SWIFT_INLINE_BITFIELD_EMPTY(TypeDecl, ValueDecl);
+  SWIFT_INLINE_BITFIELD_EMPTY(AbstractTypeParamDecl, TypeDecl);
 
   SWIFT_INLINE_BITFIELD_FULL(GenericTypeParamDecl, AbstractTypeParamDecl, 16+16,
     : NumPadBits,
@@ -472,7 +473,7 @@ class alignas(1 << DeclAlignInBits) Decl {
     Index : 16
   );
 
-  SWIFT_INLINE_BITFIELD_EMPTY(GenericTypeDecl, ValueDecl);
+  SWIFT_INLINE_BITFIELD_EMPTY(GenericTypeDecl, TypeDecl);
 
   SWIFT_INLINE_BITFIELD(TypeAliasDecl, GenericTypeDecl, 1+1,
     /// Whether the typealias forwards perfectly to its underlying type.
@@ -572,6 +573,22 @@ class alignas(1 << DeclAlignInBits) Decl {
     HasAnyUnavailableValues : 1
   );
 
+  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1,
+    /// If the module was or is being compiled with `-enable-testing`.
+    TestingEnabled : 1,
+
+    /// If the module failed to load
+    FailedToLoad : 1,
+
+    /// Whether the module is resilient.
+    ///
+    /// \sa ResilienceStrategy
+    RawResilienceStrategy : 1,
+
+    /// Whether all imports have been resolved. Used to detect circular imports.
+    HasResolvedImports : 1
+  );
+
   SWIFT_INLINE_BITFIELD(PrecedenceGroupDecl, Decl, 1+2,
     /// Is this an assignment operator?
     IsAssignment : 1,

include/swift/AST/Module.h

@@ -241,13 +241,6 @@ class ModuleDecl : public DeclContext, public TypeDecl {
   /// \see EntryPointInfoTy
   EntryPointInfoTy EntryPointInfo;
 
-  struct {
-    unsigned TestingEnabled : 1;
-    unsigned FailedToLoad : 1;
-    unsigned ResilienceStrategy : 1;
-    unsigned HasResolvedImports : 1;
-  } Flags;
-
   ModuleDecl(Identifier name, ASTContext &ctx);
 
 public:
@@ -284,32 +277,32 @@ class ModuleDecl : public DeclContext, public TypeDecl {
 
   /// Returns true if this module was or is being compiled for testing.
   bool isTestingEnabled() const {
-    return Flags.TestingEnabled;
+    return Bits.ModuleDecl.TestingEnabled;
   }
   void setTestingEnabled(bool enabled = true) {
-    Flags.TestingEnabled = enabled;
+    Bits.ModuleDecl.TestingEnabled = enabled;
   }
 
   /// Returns true if there was an error trying to load this module.
   bool failedToLoad() const {
-    return Flags.FailedToLoad;
+    return Bits.ModuleDecl.FailedToLoad;
   }
   void setFailedToLoad(bool failed = true) {
-    Flags.FailedToLoad = failed;
+    Bits.ModuleDecl.FailedToLoad = failed;
   }
 
   bool hasResolvedImports() const {
-    return Flags.HasResolvedImports;
+    return Bits.ModuleDecl.HasResolvedImports;
   }
   void setHasResolvedImports() {
-    Flags.HasResolvedImports = true;
+    Bits.ModuleDecl.HasResolvedImports = true;
   }
 
   ResilienceStrategy getResilienceStrategy() const {
-    return ResilienceStrategy(Flags.ResilienceStrategy);
+    return ResilienceStrategy(Bits.ModuleDecl.RawResilienceStrategy);
   }
   void setResilienceStrategy(ResilienceStrategy strategy) {
-    Flags.ResilienceStrategy = unsigned(strategy);
+    Bits.ModuleDecl.RawResilienceStrategy = unsigned(strategy);
   }
 
   /// Look up a (possibly overloaded) value set at top-level scope

lib/AST/Module.cpp

@@ -353,8 +353,8 @@ void SourceLookupCache::invalidate() {
 
 ModuleDecl::ModuleDecl(Identifier name, ASTContext &ctx)
   : DeclContext(DeclContextKind::Module, nullptr),
-    TypeDecl(DeclKind::Module, &ctx, name, SourceLoc(), { }),
-    Flags() {
+    TypeDecl(DeclKind::Module, &ctx, name, SourceLoc(), { }) {
+
   ctx.addDestructorCleanup(*this);
   setImplicit();
   setInterfaceType(ModuleType::get(this));