[clang] Module global init mangling

C++20 modules require emission of an initializer function, which is
called by importers of the module.  This implements the mangling for
that function.  It is the one place the ABI exposes partition names in
symbols -- but fortunately only needed by other TUs of that same module.

Reviewed By: bruno

Differential Revision: https://reviews.llvm.org/D122741

clang/include/clang/AST/Mangle.h

@@ -199,6 +199,8 @@ public:
 
   virtual void mangleDynamicStermFinalizer(const VarDecl *D, raw_ostream &) = 0;
 
+  virtual void mangleModuleInitializer(const Module *Module, raw_ostream &) = 0;
+
   // This has to live here, otherwise the CXXNameMangler won't have access to
   // it.
   virtual DiscriminatorOverrideTy getDiscriminatorOverride() const = 0;

clang/lib/AST/ItaniumMangle.cpp

@@ -130,6 +130,8 @@ public:
 
   void mangleLambdaSig(const CXXRecordDecl *Lambda, raw_ostream &) override;
 
+  void mangleModuleInitializer(const Module *Module, raw_ostream &) override;
+
   bool getNextDiscriminator(const NamedDecl *ND, unsigned &disc) {
     // Lambda closure types are already numbered.
     if (isLambda(ND))
@@ -438,7 +440,7 @@ public:
   void mangleType(QualType T);
   void mangleNameOrStandardSubstitution(const NamedDecl *ND);
   void mangleLambdaSig(const CXXRecordDecl *Lambda);
-  void mangleModuleNamePrefix(StringRef Name);
+  void mangleModuleNamePrefix(StringRef Name, bool IsPartition = false);
 
 private:
 
@@ -1057,8 +1059,8 @@ void CXXNameMangler::mangleModuleName(const NamedDecl *ND) {
 //		 ::= <module-name> <module-subname>
 //	 	 ::= <substitution>
 // <module-subname> ::= W <source-name>
-//		    ::= W P <source-name> # not (yet) needed
-void CXXNameMangler::mangleModuleNamePrefix(StringRef Name) {
+//		    ::= W P <source-name>
+void CXXNameMangler::mangleModuleNamePrefix(StringRef Name, bool IsPartition) {
   //  <substitution> ::= S <seq-id> _
   auto It = ModuleSubstitutions.find(Name);
   if (It != ModuleSubstitutions.end()) {
@@ -1072,10 +1074,14 @@ void CXXNameMangler::mangleModuleNamePrefix(StringRef Name) {
   auto Parts = Name.rsplit('.');
   if (Parts.second.empty())
     Parts.second = Parts.first;
-  else
-    mangleModuleNamePrefix(Parts.first);
+  else {
+    mangleModuleNamePrefix(Parts.first, IsPartition);
+    IsPartition = false;
+  }
 
   Out << 'W';
+  if (IsPartition)
+    Out << 'P';
   Out << Parts.second.size() << Parts.second;
   ModuleSubstitutions.insert({Name, SeqID++});
 }
@@ -6533,6 +6539,21 @@ void ItaniumMangleContextImpl::mangleLambdaSig(const CXXRecordDecl *Lambda,
   Mangler.mangleLambdaSig(Lambda);
 }
 
+void ItaniumMangleContextImpl::mangleModuleInitializer(const Module *M,
+                                                       raw_ostream &Out) {
+  // <special-name> ::= GI <module-name>  # module initializer function
+  CXXNameMangler Mangler(*this, Out);
+  Mangler.getStream() << "_ZGI";
+  Mangler.mangleModuleNamePrefix(M->getPrimaryModuleInterfaceName());
+  if (M->isModulePartition()) {
+    // The partition needs including, as partitions can have them too.
+    auto Partition = M->Name.find(':');
+    Mangler.mangleModuleNamePrefix(
+        StringRef(&M->Name[Partition + 1], M->Name.size() - Partition - 1),
+        /*IsPartition*/ true);
+  }
+}
+
 ItaniumMangleContext *ItaniumMangleContext::create(ASTContext &Context,
                                                    DiagnosticsEngine &Diags,
                                                    bool IsAux) {