[NFC] [C++20] [Modules] Use new class CXX20ModulesGenerator to generate module file for C++20 modules instead of PCHGenerator

Previously we're re-using PCHGenerator to generate the module file for
C++20 modules. But this is slighty more or less odd. This patch tries
to use a new class 'CXX20ModulesGenerator' to generate the module file
for C++20 modules.

Author: ChuanqiXu9

clang/include/clang/Serialization/ASTWriter.h

@@ -928,17 +928,30 @@ class PCHGenerator : public SemaConsumer {
   bool hasEmittedPCH() const { return Buffer->IsComplete; }
 };
 
-class ReducedBMIGenerator : public PCHGenerator {
+class CXX20ModulesGenerator : public PCHGenerator {
 protected:
   virtual Module *getEmittingModule(ASTContext &Ctx) override;
 
+  CXX20ModulesGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+                        StringRef OutputFile, bool GeneratingReducedBMI);
+
 public:
-  ReducedBMIGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
-                      StringRef OutputFile);
+  CXX20ModulesGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+                        StringRef OutputFile)
+      : CXX20ModulesGenerator(PP, ModuleCache, OutputFile,
+                              /*GeneratingReducedBMI=*/false) {}
 
   void HandleTranslationUnit(ASTContext &Ctx) override;
 };
 
+class ReducedBMIGenerator : public CXX20ModulesGenerator {
+public:
+  ReducedBMIGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+                      StringRef OutputFile)
+      : CXX20ModulesGenerator(PP, ModuleCache, OutputFile,
+                              /*GeneratingReducedBMI=*/true) {}
+};
+
 /// If we can elide the definition of \param D in reduced BMI.
 ///
 /// Generally, we can elide the definition of a declaration if it won't affect

clang/lib/Frontend/FrontendActions.cpp

@@ -272,14 +272,10 @@ bool GenerateModuleInterfaceAction::BeginSourceFileAction(
 std::unique_ptr<ASTConsumer>
 GenerateModuleInterfaceAction::CreateASTConsumer(CompilerInstance &CI,
                                                  StringRef InFile) {
-  CI.getHeaderSearchOpts().ModulesSkipDiagnosticOptions = true;
-  CI.getHeaderSearchOpts().ModulesSkipHeaderSearchPaths = true;
-  CI.getHeaderSearchOpts().ModulesSkipPragmaDiagnosticMappings = true;
-
-  std::vector<std::unique_ptr<ASTConsumer>> Consumers =
-      CreateMultiplexConsumer(CI, InFile);
-  if (Consumers.empty())
-    return nullptr;
+  std::vector<std::unique_ptr<ASTConsumer>> Consumers;
+  Consumers.push_back(std::make_unique<CXX20ModulesGenerator>(
+      CI.getPreprocessor(), CI.getModuleCache(),
+      CI.getFrontendOpts().OutputFile));
 
   if (CI.getFrontendOpts().GenReducedBMI &&
       !CI.getFrontendOpts().ModuleOutputPath.empty()) {

clang/lib/Serialization/GeneratePCH.cpp

@@ -88,31 +88,28 @@ ASTDeserializationListener *PCHGenerator::GetASTDeserializationListener() {
   return &Writer;
 }
 
-ReducedBMIGenerator::ReducedBMIGenerator(Preprocessor &PP,
-                                         InMemoryModuleCache &ModuleCache,
-                                         StringRef OutputFile)
+CXX20ModulesGenerator::CXX20ModulesGenerator(Preprocessor &PP,
+                                             InMemoryModuleCache &ModuleCache,
+                                             StringRef OutputFile,
+                                             bool GeneratingReducedBMI)
     : PCHGenerator(
           PP, ModuleCache, OutputFile, llvm::StringRef(),
           std::make_shared<PCHBuffer>(),
           /*Extensions=*/ArrayRef<std::shared_ptr<ModuleFileExtension>>(),
           /*AllowASTWithErrors*/ false, /*IncludeTimestamps=*/false,
           /*BuildingImplicitModule=*/false, /*ShouldCacheASTInMemory=*/false,
-          /*GeneratingReducedBMI=*/true) {}
+          GeneratingReducedBMI) {}
 
-Module *ReducedBMIGenerator::getEmittingModule(ASTContext &Ctx) {
+Module *CXX20ModulesGenerator::getEmittingModule(ASTContext &Ctx) {
   Module *M = Ctx.getCurrentNamedModule();
   assert(M && M->isNamedModuleUnit() &&
-         "ReducedBMIGenerator should only be used with C++20 Named modules.");
+         "CXX20ModulesGenerator should only be used with C++20 Named modules.");
   return M;
 }
 
-void ReducedBMIGenerator::HandleTranslationUnit(ASTContext &Ctx) {
-  // We need to do this to make sure the size of reduced BMI not to be larger
-  // than full BMI.
-  //
+void CXX20ModulesGenerator::HandleTranslationUnit(ASTContext &Ctx) {
   // FIMXE: We'd better to wrap such options to a new class ASTWriterOptions
   // since this is not about searching header really.
-  // FIXME2: We'd better to move the class writing full BMI with reduced BMI.
   HeaderSearchOptions &HSOpts =
       getPreprocessor().getHeaderSearchInfo().getHeaderSearchOpts();
   HSOpts.ModulesSkipDiagnosticOptions = true;

clang/test/Modules/pr67893.cppm

@@ -5,7 +5,7 @@
 // RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++20 %t/a.cppm \
 // RUN:      -emit-module-interface -o %t/a.pcm
 // RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++20 %t/m.cppm \
-// RUN:      -emit-module-interface -fprebuilt-module-path=%t
+// RUN:      -emit-module-interface -fprebuilt-module-path=%t -o %t/m.pcm
 // RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++20 %t/m.pcm  \
 // RUN:      -fprebuilt-module-path=%t -S -emit-llvm -o - | FileCheck %t/m.cppm
 

clang/test/Modules/search-partitions.cpp

@@ -11,7 +11,7 @@
 // RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/partition3.cpp \
 // RUN:  -o %t/A-Part3.pcm
 
-// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/moduleA.cpp \
+// RUN: %clang_cc1 -std=c++20 %t/moduleA.cpp -fsyntax-only -verify \
 // RUN:  -fprebuilt-module-path=%t
 
 // Test again with reduced BMI
@@ -28,9 +28,7 @@
 // RUN: %clang_cc1 -std=c++20 -emit-reduced-module-interface %t/partition3.cpp \
 // RUN:  -o %t/A-Part3.pcm
 
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only %t/moduleA.cpp -fprebuilt-module-path=%t 
-
-// expected-no-diagnostics
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %t/moduleA.cpp -fprebuilt-module-path=%t 
 
 //--- partition1.cpp
 export module A:Part1;
@@ -50,7 +48,7 @@ export module A:Part3;
 int part3();
 
 //--- moduleA.cpp
-
+// expected-no-diagnostics
 export module A;
 
 import :Part1;