Re-use GlobalResolution map for key de-duplication

Author: mingmingl-llvm

llvm/include/llvm/LTO/LTO.h

@@ -353,11 +353,10 @@ class LTO {
     DenseMap<GlobalValue::GUID, StringRef> PrevailingModuleForGUID;
   } ThinLTO;
 
-  std::unique_ptr<llvm::BumpPtrAllocator> Alloc =
-      std::make_unique<BumpPtrAllocator>();
+  std::unique_ptr<llvm::BumpPtrAllocator> Alloc;
 
-  std::unique_ptr<llvm::UniqueStringSaver> UniqueSymbolSaver =
-      std::make_unique<llvm::UniqueStringSaver>(*Alloc);
+  // Symbol saver for global resolution map.
+  std::unique_ptr<llvm::StringSaver> GlobalResolutionSymbolSaver;
 
   // The global resolution for a particular (mangled) symbol name. This is in
   // particular necessary to track whether each symbol can be internalized.

llvm/lib/LTO/LTO.cpp

@@ -78,6 +78,10 @@ cl::opt<bool> EnableLTOInternalization(
     "enable-lto-internalization", cl::init(true), cl::Hidden,
     cl::desc("Enable global value internalization in LTO"));
 
+static cl::opt<bool>
+    LTOKeepSymbolCopies("lto-keep-symbol-copies", cl::init(false), cl::Hidden,
+                        cl::desc("Keep copies of symbols in LTO indexing"));
+
 /// Indicate we are linking with an allocator that supports hot/cold operator
 /// new interfaces.
 extern cl::opt<bool> SupportsHotColdNew;
@@ -609,7 +613,12 @@ LTO::LTO(Config Conf, ThinBackend Backend,
       ThinLTO(std::move(Backend)),
       GlobalResolutions(
           std::make_unique<DenseMap<StringRef, GlobalResolution>>()),
-      LTOMode(LTOMode) {}
+      LTOMode(LTOMode) {
+  if (Conf.KeepSymbolNameCopies || LTOKeepSymbolCopies) {
+    Alloc = std::make_unique<BumpPtrAllocator>();
+    GlobalResolutionSymbolSaver = std::make_unique<llvm::StringSaver>(*Alloc);
+  }
+}
 
 // Requires a destructor for MapVector<BitcodeModule>.
 LTO::~LTO() = default;
@@ -628,8 +637,9 @@ void LTO::addModuleToGlobalRes(ArrayRef<InputFile::Symbol> Syms,
     SymbolResolution Res = *ResI++;
 
     StringRef SymbolName = Sym.getName();
-    if (Conf.KeepSymbolNameCopies)
-      SymbolName = UniqueSymbolSaver->save(SymbolName);
+    // Keep copies of symbols if the client of LTO says so.
+    if (GlobalResolutionSymbolSaver && !GlobalResolutions->contains(SymbolName))
+      SymbolName = GlobalResolutionSymbolSaver->save(SymbolName);
 
     auto &GlobalRes = (*GlobalResolutions)[SymbolName];
     GlobalRes.UnnamedAddr &= Sym.isUnnamedAddr();
@@ -1803,7 +1813,7 @@ Error LTO::runThinLTO(AddStreamFn AddStream, FileCache Cache,
   // and export lists.
   GlobalResolutions.reset();
   // Reset the bump pointer allocator to release its memory.
-  UniqueSymbolSaver.reset();
+  GlobalResolutionSymbolSaver.reset();
   Alloc.reset();
 
   if (Conf.OptLevel > 0)