Replace StringMap with DenseMap when the keys don't need to be owned

StringMap always copies its strings into its own storage. A DenseMap
of StringRefs has the same caveats as any other use of StringRef, but
in the cases I've changed the string has very clear ownership that
outlives the map.

No functionality change, but should reduce memory usage and malloc
traffic a little.

Author: jrose-apple

include/swift/Basic/SourceManager.h

@@ -31,13 +31,13 @@ class SourceManager {
   unsigned CodeCompletionOffset;
 
   /// Associates buffer identifiers to buffer IDs.
-  llvm::StringMap<unsigned> BufIdentIDMap;
+  llvm::DenseMap<StringRef, unsigned> BufIdentIDMap;
 
   /// A cache mapping buffer identifiers to vfs Status entries.
   ///
   /// This is as much a hack to prolong the lifetime of status objects as it is
   /// to speed up stats.
-  mutable llvm::StringMap<clang::vfs::Status> StatusCache;
+  mutable llvm::DenseMap<StringRef, clang::vfs::Status> StatusCache;
 
   // \c #sourceLocation directive handling.
   struct VirtualFile {

lib/ClangImporter/ClangImporter.cpp

@@ -3288,7 +3288,7 @@ bool ClangImporter::Implementation::forEachLookupTable(
   // Collect and sort the set of module names.
   SmallVector<StringRef, 4> moduleNames;
   for (const auto &entry : LookupTables) {
-    moduleNames.push_back(entry.first());
+    moduleNames.push_back(entry.first);
   }
   llvm::array_pod_sort(moduleNames.begin(), moduleNames.end());
 
@@ -3596,7 +3596,7 @@ void ClangImporter::Implementation::dumpSwiftLookupTables() {
   // Sort the module names so we can print in a deterministic order.
   SmallVector<StringRef, 4> moduleNames;
   for (const auto &lookupTable : LookupTables) {
-    moduleNames.push_back(lookupTable.first());
+    moduleNames.push_back(lookupTable.first);
   }
   array_pod_sort(moduleNames.begin(), moduleNames.end());
 

lib/ClangImporter/ImporterImpl.h

@@ -279,7 +279,8 @@ struct PlatformAvailability {
 };
 }
 
-using LookupTableMap = llvm::StringMap<std::unique_ptr<SwiftLookupTable>>;
+using LookupTableMap =
+    llvm::DenseMap<StringRef, std::unique_ptr<SwiftLookupTable>>;
 
 /// The result of importing a clang type. It holds both the Swift Type
 /// as well as a bool in which 'true' indicates either:
@@ -489,10 +490,6 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
     return getNameImporter().getEnumKind(decl);
   }
 
-  // TODO: drop this accessor as soon as we further de-couple the swift name
-  // lookup tables from the Impl.
-  LookupTableMap &getLookupTables() { return LookupTables; }
-
 private:
   /// A mapping from imported declarations to their "alternate" declarations,
   /// for cases where a single Clang declaration is imported to two

lib/Driver/Driver.cpp

@@ -586,7 +586,7 @@ static bool populateOutOfDateMap(InputInfoMap &map,
     // If a file was removed, we've lost its dependency info. Rebuild everything.
     // FIXME: Can we do better?
     if (ShowIncrementalBuildDecisions) {
-      llvm::StringSet<> inputArgs;
+      llvm::DenseSet<StringRef> inputArgs;
       for (auto &inputPair : inputs) {
         inputArgs.insert(inputPair.second->getValue());
       }
@@ -1181,7 +1181,7 @@ static bool checkInputExistence(const Driver &D, const DerivedArgList &Args,
 void Driver::buildInputs(const ToolChain &TC,
                          const DerivedArgList &Args,
                          InputFileList &Inputs) const {
-  llvm::StringMap<StringRef> SourceFileNames;
+  llvm::DenseMap<StringRef, StringRef> SourceFileNames;
 
   for (Arg *A : Args) {
     if (A->getOption().getKind() == Option::InputClass) {

lib/Driver/ToolChain.cpp

@@ -290,7 +290,7 @@ static void
 sortJobsToMatchCompilationInputs(ArrayRef<const Job *> unsortedJobs,
                                  SmallVectorImpl<const Job *> &sortedJobs,
                                  Compilation &C) {
-  llvm::StringMap<const Job *> jobsByInput;
+  llvm::DenseMap<StringRef, const Job *> jobsByInput;
   for (const Job *J : unsortedJobs) {
     const CompileJobAction *CJA = cast<CompileJobAction>(&J->getSource());
     const InputAction *IA = findSingleSwiftInput(CJA);

lib/Driver/ToolChains.cpp

@@ -503,7 +503,7 @@ void ToolChain::JobContext::addFrontendCommandLineInputArguments(
     const bool mayHavePrimaryInputs, const bool useFileList,
     const bool usePrimaryFileList, const bool filterByType,
     ArgStringList &arguments) const {
-  llvm::StringSet<> primaries;
+  llvm::DenseSet<StringRef> primaries;
 
   if (mayHavePrimaryInputs) {
     for (const Action *A : InputActions) {

lib/IRGen/IRGen.cpp

@@ -1010,7 +1010,7 @@ static void performParallelIRGeneration(
                   PrimaryGM->addLinkLibrary(linkLib);
                 });
 
-  llvm::StringSet<> referencedGlobals;
+  llvm::DenseSet<StringRef> referencedGlobals;
 
   for (auto it = irgen.begin(); it != irgen.end(); ++it) {
     IRGenModule *IGM = it->second;

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -65,8 +65,8 @@ static bool isAnyObjectOrAny(Type type) {
 
 /// Returns true if \p name matches a keyword in any Clang language mode.
 static bool isClangKeyword(Identifier name) {
-  static const llvm::StringSet<> keywords = []{
-    llvm::StringSet<> set;
+  static const llvm::DenseSet<StringRef> keywords = []{
+    llvm::DenseSet<StringRef> set;
     // FIXME: clang::IdentifierInfo /nearly/ has the API we need to do this
     // in a more principled way, but not quite.
 #define KEYWORD(SPELLING, FLAGS) \

lib/SIL/SILVerifier.cpp

@@ -5065,7 +5065,7 @@ void SILModule::verify() const {
     return;
 #endif
   // Uniquing set to catch symbol name collisions.
-  llvm::StringSet<> symbolNames;
+  llvm::DenseSet<StringRef> symbolNames;
 
   // When merging partial modules, we only link functions from the current
   // module, without enabling "LinkAll" mode or running the SILLinker pass;