[NFC] [AST] Introduce Decl::isInAnotherModuleUnit and Decl::shouldEmi…

…tInExternalSource

Motivated by the review process in
llvm#75912. This can also help to
simplify the code slightly.

clang/include/clang/AST/DeclBase.h

@@ -670,6 +670,13 @@ class alignas(8) Decl {
   /// Whether this declaration comes from another module unit.
   bool isInAnotherModuleUnit() const;
 
+  /// Whether the definition of the declaration should be emitted in external
+  /// sources.
+  bool shouldEmitInExternalSource() const;
+
+  /// Whether this declaration comes from a named module;
+  bool isInNamedModule() const;
+
   /// Whether this declaration comes from explicit global module.
   bool isFromExplicitGlobalModule() const;
 

clang/lib/AST/ASTContext.cpp

@@ -12018,7 +12018,7 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
     return false;
 
   // Variables in other module units shouldn't be forced to be emitted.
-  if (VD->isInAnotherModuleUnit())
+  if (VD->shouldEmitInExternalSource())
     return false;
 
   // Variables that can be needed in other TUs are required.

clang/lib/AST/Decl.cpp

@@ -1174,13 +1174,6 @@ Linkage NamedDecl::getLinkageInternal() const {
       .getLinkage();
 }
 
-/// Determine whether D is attached to a named module.
-static bool isInNamedModule(const NamedDecl *D) {
-  if (auto *M = D->getOwningModule())
-    return M->isNamedModule();
-  return false;
-}
-
 static bool isExportedFromModuleInterfaceUnit(const NamedDecl *D) {
   // FIXME: Handle isModulePrivate.
   switch (D->getModuleOwnershipKind()) {
@@ -1190,7 +1183,7 @@ static bool isExportedFromModuleInterfaceUnit(const NamedDecl *D) {
     return false;
   case Decl::ModuleOwnershipKind::Visible:
   case Decl::ModuleOwnershipKind::VisibleWhenImported:
-    return isInNamedModule(D);
+    return D->isInNamedModule();
   }
   llvm_unreachable("unexpected module ownership kind");
 }
@@ -1208,7 +1201,7 @@ Linkage NamedDecl::getFormalLinkage() const {
   // [basic.namespace.general]/p2
   //   A namespace is never attached to a named module and never has a name with
   //   module linkage.
-  if (isInNamedModule(this) && InternalLinkage == Linkage::External &&
+  if (isInNamedModule() && InternalLinkage == Linkage::External &&
       !isExportedFromModuleInterfaceUnit(
           cast<NamedDecl>(this->getCanonicalDecl())) &&
       !isa<NamespaceDecl>(this))

clang/lib/AST/DeclBase.cpp

@@ -1100,23 +1100,22 @@ bool Decl::isInExportDeclContext() const {
 bool Decl::isInAnotherModuleUnit() const {
   auto *M = getOwningModule();
 
-  if (!M)
+  if (!M || !M->isNamedModule())
     return false;
 
-  M = M->getTopLevelModule();
-  // FIXME: It is problematic if the header module lives in another module
-  // unit. Consider to fix this by techniques like
-  // ExternalASTSource::hasExternalDefinitions.
-  if (M->isHeaderLikeModule())
-    return false;
+  return M != getASTContext().getCurrentNamedModule();
+}
 
-  // A global module without parent implies that we're parsing the global
-  // module. So it can't be in another module unit.
-  if (M->isGlobalModule())
+bool Decl::shouldEmitInExternalSource() const {
+  ExternalASTSource *Source = getASTContext().getExternalSource();
+  if (!Source)
     return false;
 
-  assert(M->isNamedModule() && "New module kind?");
-  return M != getASTContext().getCurrentNamedModule();
+  return Source->hasExternalDefinitions(this) == ExternalASTSource::EK_Always;
+}
+
+bool Decl::isInNamedModule() const {
+  return getOwningModule() && getOwningModule()->isNamedModule();
 }
 
 bool Decl::isFromExplicitGlobalModule() const {

clang/lib/CodeGen/CGVTables.cpp

@@ -1200,7 +1200,7 @@ bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
   assert(Def && "The body of the key function is not assigned to Def?");
   // If the non-inline key function comes from another module unit, the vtable
   // must be defined there.
-  return Def->isInAnotherModuleUnit() && !Def->isInlineSpecified();
+  return Def->shouldEmitInExternalSource() && !Def->isInlineSpecified();
 }
 
 /// Given that we're currently at the end of the translation unit, and

clang/lib/Sema/SemaDecl.cpp

@@ -10244,7 +10244,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     // check at the end of the TU (or when the PMF starts) to see that we
     // have a definition at that point.
     if (isInline && !D.isFunctionDefinition() && getLangOpts().CPlusPlus20 &&
-        NewFD->hasOwningModule() && NewFD->getOwningModule()->isNamedModule()) {
+        NewFD->isInNamedModule()) {
       PendingInlineFuncDecls.insert(NewFD);
     }
   }

clang/lib/Serialization/ASTWriter.cpp

@@ -6508,10 +6508,12 @@ void ASTRecordWriter::AddCXXDefinitionData(const CXXRecordDecl *D) {
     // computed.
     Record->push_back(D->getODRHash());
 
-  bool ModulesDebugInfo =
-      Writer->Context->getLangOpts().ModulesDebugInfo && !D->isDependentType();
-  Record->push_back(ModulesDebugInfo);
-  if (ModulesDebugInfo)
+  bool ModulesCodegen =
+      !D->isDependentType() &&
+     (Writer->Context->getLangOpts().ModulesDebugInfo ||
+      D->isInNamedModule());
+  Record->push_back(ModulesCodegen);
+  if (ModulesCodegen)
     Writer->AddDeclRef(D, Writer->ModularCodegenDecls);
 
   // IsLambda bit is already saved.