Clarify ownership of DepTracker.

Author: David Ungar

include/swift/Frontend/Frontend.h

@@ -336,7 +336,8 @@ class CompilerInstance {
   std::unique_ptr<ASTContext> Context;
   std::unique_ptr<SILModule> TheSILModule;
 
-  DependencyTracker *DepTracker = nullptr;
+  /// Null if no tracker.
+  std::unique_ptr<DependencyTracker> DepTracker;
 
   ModuleDecl *MainModule = nullptr;
   SerializedModuleLoader *SML = nullptr;
@@ -408,13 +409,11 @@ class CompilerInstance {
     Diagnostics.addConsumer(*DC);
   }
 
-  void setDependencyTracker(DependencyTracker *DT) {
+  void createDependencyTracker() {
     assert(!Context && "must be called before setup()");
-    DepTracker = DT;
-  }
-  DependencyTracker *getDependencyTracker() {
-    return DepTracker;
+    DepTracker = llvm::make_unique<DependencyTracker>();
   }
+  DependencyTracker *getDependencyTracker() { return DepTracker.get(); }
 
   /// Set the SIL module for this compilation instance.
   ///

lib/Frontend/Frontend.cpp

@@ -197,10 +197,10 @@ bool CompilerInstance::setUpModuleLoaders() {
     Context->addModuleLoader(SourceLoader::create(*Context,
                                                   !immediate,
                                                   enableResilience,
-                                                  DepTracker));
+                                                  getDependencyTracker()));
   }
   {
-    auto SML = SerializedModuleLoader::create(*Context, DepTracker);
+    auto SML = SerializedModuleLoader::create(*Context, getDependencyTracker());
     this->SML = SML.get();
     Context->addModuleLoader(std::move(SML));
   }
@@ -210,7 +210,7 @@ bool CompilerInstance::setUpModuleLoaders() {
     // knowledge.
     auto clangImporter =
         ClangImporter::create(*Context, Invocation.getClangImporterOptions(),
-                              Invocation.getPCHHash(), DepTracker);
+                              Invocation.getPCHHash(), getDependencyTracker());
     if (!clangImporter) {
       Diagnostics.diagnose(SourceLoc(), diag::error_clang_importer_create_fail);
       return true;

lib/FrontendTool/FrontendTool.cpp

@@ -1756,17 +1756,10 @@ int swift::performFrontend(ArrayRef<const char *> Args,
     enableDiagnosticVerifier(Instance->getSourceMgr());
   }
 
-  // Do not move into the following block. Even though it appears to not be
-  // referenced, depTracker must live as long as this activation record.
-  DependencyTracker depTracker;
-  {
-    const FrontendInputsAndOutputs &io =
-        Invocation.getFrontendOptions().InputsAndOutputs;
-    if (io.hasDependencyTrackerPath() ||
-        !Invocation.getFrontendOptions().IndexStorePath.empty()) {
-      Instance->setDependencyTracker(&depTracker);
-    }
-  }
+  if (Invocation.getFrontendOptions()
+          .InputsAndOutputs.hasDependencyTrackerPath() ||
+      !Invocation.getFrontendOptions().IndexStorePath.empty())
+    Instance->createDependencyTracker();
 
   if (Instance->setup(Invocation)) {
     return finishDiagProcessing(1);