[Dependency Scanning] Keep track of how many filesystem module lookups the dependency scanner performs on a given scan

Author: artemcm

include/swift/AST/DiagnosticsCommon.def

@@ -218,6 +218,9 @@ WARNING(warn_scanner_deserialize_failed, none,
 REMARK(remark_reuse_cache, none,
        "Re-using serialized module scanning dependency cache from: '%0'.", (StringRef))
 
+REMARK(remark_scanner_uncached_lookups, none,
+       "Module Dependency Scanner queries executed: '%0'.", (unsigned))
+
 REMARK(remark_save_cache, none,
        "Serializing module scanning dependency cache to: '%0'.", (StringRef))
 

include/swift/DependencyScan/ModuleDependencyScanner.h

@@ -95,6 +95,9 @@ class ModuleDependencyScanner {
   getNamedSwiftModuleDependencyInfo(StringRef moduleName,
                                     ModuleDependenciesCache &cache);
 
+  /// How many filesystem lookups were performed by the scanner
+  unsigned getNumLookups() { return NumLookups; }
+
 private:
   /// Main routine that computes imported module dependency transitive
   /// closure for the given module.
@@ -166,6 +169,8 @@ class ModuleDependencyScanner {
   llvm::StdThreadPool ScanningThreadPool;
   /// Protect worker access.
   std::mutex WorkersLock;
+  /// Count of filesystem queries performed
+  std::atomic<unsigned> NumLookups = 0;
 };
 
 } // namespace swift

lib/DependencyScan/ModuleDependencyCacheSerialization.cpp

@@ -1783,6 +1783,7 @@ void ModuleDependenciesCacheSerializer::collectStringsAndArrays(
         addIdentifier(swiftTextDeps->textualModuleDetails
                           .CASBridgingHeaderIncludeTreeRootID);
         addIdentifier(swiftTextDeps->moduleCacheKey);
+        addIdentifier(swiftTextDeps->userModuleVersion);
         break;
       }
       case swift::ModuleDependencyKind::SwiftBinary: {

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -248,6 +248,7 @@ ModuleDependencyScanningWorker::scanFilesystemForClangModuleDependency(
 template <typename Function, typename... Args>
 auto ModuleDependencyScanner::withDependencyScanningWorker(Function &&F,
                                                            Args &&...ArgList) {
+  NumLookups++;
   auto getWorker = [this]() -> std::unique_ptr<ModuleDependencyScanningWorker> {
     std::lock_guard<std::mutex> guard(WorkersLock);
     // If we have run out of workers, something has gone wrong as we must never

lib/DependencyScan/ScanDependencies.cpp

@@ -1529,17 +1529,12 @@ swift::dependencies::performModuleScan(
 
   // Identify imports of the main module and add an entry for it
   // to the dependency graph.
-  auto mainModuleDepInfo =
-      scanner.getMainModuleDependencyInfo(instance.getMainModule());
   auto mainModuleName = instance.getMainModule()->getNameStr();
   auto mainModuleID = ModuleDependencyID{mainModuleName.str(),
                                          ModuleDependencyKind::SwiftSource};
-  // We may be re-using an instance of the cache which already contains
-  // an entry for this module.
-  if (cache.findDependency(mainModuleID))
-    cache.updateDependency(mainModuleID, std::move(*mainModuleDepInfo));
-  else
-    cache.recordDependency(mainModuleName, std::move(*mainModuleDepInfo));
+  if (!cache.hasDependency(mainModuleID))
+    cache.recordDependency(mainModuleName,
+                           *scanner.getMainModuleDependencyInfo(instance.getMainModule()));
 
   // Perform the full module scan starting at the main module.
   auto allModules = scanner.performDependencyScan(mainModuleID, cache);
@@ -1552,6 +1547,10 @@ swift::dependencies::performModuleScan(
                                         topologicallySortedModuleList);
   resolveImplicitLinkLibraries(instance, cache);
   updateDependencyTracker(instance, cache, allModules);
+
+  if (instance.getInvocation().getFrontendOptions().EmitDependencyScannerCacheRemarks)
+    instance.getASTContext().Diags.diagnose(SourceLoc(), diag::remark_scanner_uncached_lookups, scanner.getNumLookups());
+
   return generateFullDependencyGraph(instance, diagnosticCollector, cache,
                                      topologicallySortedModuleList);
 }