[clang-tools-extra] [clangd] [Modules] Support Reusable Modules Builder (PR #106683)

[Chuanqi Xu via cfe-commits]

================
@@ -316,36 +287,169 @@ llvm::Error buildModuleFile(llvm::StringRef ModuleName,
   if (Clang->getDiagnostics().hasErrorOccurred())
     return llvm::createStringError("Compilation failed");
 
-  BuiltModuleFiles.addModuleFile(ModuleName, Inputs.CompileCommand.Output);
-  return llvm::Error::success();
+  return ModuleFile{ModuleName, Inputs.CompileCommand.Output};
+}
+
+bool ReusablePrerequisiteModules::canReuse(
+    const CompilerInvocation &CI,
+    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS) const {
+  if (RequiredModules.empty())
+    return true;
+
+  SmallVector<StringRef> BMIPaths;
+  for (auto &MF : RequiredModules)
+    BMIPaths.push_back(MF->ModuleFilePath);
+  return IsModuleFilesUpToDate(BMIPaths, *this, VFS);
 }
 } // namespace
 
+class ModulesBuilder::ModuleFileCache {
+public:
+  ModuleFileCache(const GlobalCompilationDatabase &CDB) : CDB(CDB) {}
+
+  llvm::Error
+  getOrBuildModuleFile(StringRef ModuleName, const ThreadsafeFS &TFS,
+                       ProjectModules &MDB,
+                       ReusablePrerequisiteModules &RequiredModules);
+  const GlobalCompilationDatabase &getCDB() const { return CDB; }
+
+private:
+  std::shared_ptr<ModuleFile>
+  getValidModuleFile(StringRef ModuleName, ProjectModules &MDB,
+                     const ThreadsafeFS &TFS,
+                     PrerequisiteModules &BuiltModuleFiles);
+
+  /// This should only be called by getValidModuleFile. This is unlocked version
+  /// of getValidModuleFile. The function is extracted to avoid dead locks when
+  /// recursing.
+  std::shared_ptr<ModuleFile>
+  isValidModuleFileUnlocked(StringRef ModuleName, ProjectModules &MDB,
+                            const ThreadsafeFS &TFS,
+                            PrerequisiteModules &BuiltModuleFiles);
+
+  const GlobalCompilationDatabase &CDB;
+
+  llvm::StringMap<std::shared_ptr<ModuleFile>> ModuleFiles;
+  // Mutex to guard accesses to ModuleFiles.
+  std::mutex ModuleFilesMutex;
+};
+
+std::shared_ptr<ModuleFile>
+ModulesBuilder::ModuleFileCache::isValidModuleFileUnlocked(
+    StringRef ModuleName, ProjectModules &MDB, const ThreadsafeFS &TFS,
+    PrerequisiteModules &BuiltModuleFiles) {
+  auto Iter = ModuleFiles.find(ModuleName);
+  if (Iter != ModuleFiles.end()) {
+    if (!IsModuleFileUpToDate(Iter->second->ModuleFilePath, BuiltModuleFiles,
+                              TFS.view(std::nullopt))) {
+      log("Found not-up-date module file {0} for module {1} in cache",
+          Iter->second->ModuleFilePath, ModuleName);
+      ModuleFiles.erase(Iter);
+      return nullptr;
+    }
+
+    if (llvm::any_of(
+            MDB.getRequiredModules(MDB.getSourceForModuleName(ModuleName)),
+            [&MDB, &TFS, &BuiltModuleFiles, this](auto &&RequiredModuleName) {
+              return !isValidModuleFileUnlocked(RequiredModuleName, MDB, TFS,
+                                                BuiltModuleFiles);
+            })) {
+      ModuleFiles.erase(Iter);
+      return nullptr;
+    }
+
+    return Iter->second;
+  }
+
+  log("Don't find {0} in cache", ModuleName);
+
+  return nullptr;
+}
+
+std::shared_ptr<ModuleFile> ModulesBuilder::ModuleFileCache::getValidModuleFile(
+    StringRef ModuleName, ProjectModules &MDB, const ThreadsafeFS &TFS,
+    PrerequisiteModules &BuiltModuleFiles) {
+  std::lock_guard<std::mutex> _(ModuleFilesMutex);
+
+  return isValidModuleFileUnlocked(ModuleName, MDB, TFS, BuiltModuleFiles);
+}
+
+llvm::Error ModulesBuilder::ModuleFileCache::getOrBuildModuleFile(
----------------
ChuanqiXu9 wrote:

I understand your intention. But I do think it is not good to merge them. Since `buildModuleFile` and `ModulesBuilderImpl ` are doing different things to me. `buildModuleFile` is doing the concrete, low-level things to build a module file. And `ModulesBuilderImpl` does the higher level things. e.g., decide if we're going to build the module file actually or when to build it. I think they are different logics. 


https://github.com/llvm/llvm-project/pull/106683