[clang][deps] Always use -fmodules-validate-once-per-build-session

[jansvoboda11]

Summary

The dependency scanner assumes immutable file system. In that context, we don't need to repeatedly validate PCM input files. This patch avoids that by using the existing -fmodules-validate-once-per-build-session mechanism.

Depends on D150318.

[benlangmuir]

clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp

26

I'm not sure this is guaranteed to line up with the filesystem timestamps. I wonder if you should be writing a file and reading back that stamp instead.

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

188

Why would it diagnose? This is going to be common. Maybe we should use the minimum value between the service and the existing timestamp to get the widest possible session if the build system is already providing one?

clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h

 };
 
 /// The dependency scanning service contains shared configuration and state that
 /// is used by the individual dependency scanning workers.
 class DependencyScanningService {
 public:
   DependencyScanningService(ScanningMode Mode, ScanningOutputFormat Format,
                             bool OptimizeArgs = false,
-                            bool EagerLoadModules = false);
+                            bool EagerLoadModules = false,
+                            uint64_t BuildSessionTimestamp = 0);
 
   ScanningMode getMode() const { return Mode; }
 
   ScanningOutputFormat getFormat() const { return Format; }
 
   bool canOptimizeArgs() const { return OptimizeArgs; }
 
   bool shouldEagerLoadModules() const { return EagerLoadModules; }
 
+  uint64_t getBuildSessionTimestamp() const { return BuildSessionTimestamp; }
+
   DependencyScanningFilesystemSharedCache &getSharedCache() {
     return SharedCache;
   }
 
 private:
   /// The preprocessing mode used for scanning.
   ScanningMode Mode;
   /// The output format.
   ScanningOutputFormat Format;
   /// Whether to optimize the modules' command-line arguments.
   bool OptimizeArgs;
   /// Whether to set up command-lines to load PCM files eagerly.
   bool EagerLoadModules;
+  /// The build session timestamp.
+  uint64_t BuildSessionTimestamp;
   /// The global file system cache.
   DependencyScanningFilesystemSharedCache SharedCache;
 };
 
 } // end namespace dependencies
 } // end namespace tooling
 } // end namespace clang
 
 #endif // LLVM_CLANG_TOOLING_DEPENDENCYSCANNING_DEPENDENCYSCANNINGSERVICE_H

clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp

 //===- DependencyScanningService.cpp - clang-scan-deps service ------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
 #include "llvm/Support/TargetSelect.h"
 
+#include <chrono>
+
 using namespace clang;
 using namespace tooling;
 using namespace dependencies;
 
 DependencyScanningService::DependencyScanningService(
     ScanningMode Mode, ScanningOutputFormat Format, bool OptimizeArgs,
-    bool EagerLoadModules)
+    bool EagerLoadModules, uint64_t BuildSessionTimestamp)
     : Mode(Mode), Format(Format), OptimizeArgs(OptimizeArgs),
-      EagerLoadModules(EagerLoadModules) {
+      EagerLoadModules(EagerLoadModules),
+      BuildSessionTimestamp(
+          BuildSessionTimestamp != 0
+              ? BuildSessionTimestamp
+              : std::chrono::system_clock::now().time_since_epoch().count()) {
   // Initialize targets for object file support.
   llvm::InitializeAllTargets();
   llvm::InitializeAllTargetMCs();
   llvm::InitializeAllAsmPrinters();
   llvm::InitializeAllAsmParsers();
 }

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
     ScanInstance.getPreprocessorOpts().AllowPCHWithDifferentModulesCachePath =
         true;
 
     ScanInstance.getFrontendOpts().GenerateGlobalModuleIndex = false;
     ScanInstance.getFrontendOpts().UseGlobalModuleIndex = false;
     ScanInstance.getFrontendOpts().ModulesShareFileManager = false;
     ScanInstance.getHeaderSearchOpts().ModuleFormat = "raw";
 
+    ScanInstance.getHeaderSearchOpts().ModulesValidateOncePerBuildSession =
+        true;
+    // FIXME: Consider diagnosing when this overwrites existing timestamp.
+    ScanInstance.getHeaderSearchOpts().BuildSessionTimestamp =
+        Service.getBuildSessionTimestamp();
+
     ScanInstance.setFileManager(FileMgr);
     // Support for virtual file system overlays.
     FileMgr->setVirtualFileSystem(createVFSFromCompilerInvocation(
         ScanInstance.getInvocation(), ScanInstance.getDiagnostics(),
         FileMgr->getVirtualFileSystemPtr()));
 
     ScanInstance.createSourceManager(*FileMgr);