Index: COFF/Chunks.cpp
===================================================================
--- COFF/Chunks.cpp
+++ COFF/Chunks.cpp
@@ -346,6 +346,7 @@
 void SectionChunk::printDiscardedMessage() const {
   // Removed by dead-stripping. If it's removed by ICF, ICF already
   // printed out the name, so don't repeat that here.
+// XXX
   if (Sym && this == Repl) {
     if (Discarded)
       message("Discarded comdat symbol " + Sym->getName());
Index: COFF/Config.h
===================================================================
--- COFF/Config.h
+++ COFF/Config.h
@@ -148,6 +148,9 @@
   // Used for /lldmap.
   std::string MapFile;
 
+  // Used for /redundancyReport.
+  std::string RedudancyReportFile;
+
   uint64_t ImageBase = -1;
   uint64_t StackReserve = 1024 * 1024;
   uint64_t StackCommit = 4096;
Index: COFF/Driver.cpp
===================================================================
--- COFF/Driver.cpp
+++ COFF/Driver.cpp
@@ -944,6 +944,8 @@
     Config->WriteSymtab = false;
 
   Config->MapFile = getMapFile(Args);
+  if (auto *Arg = Args.getLastArg(OPT_redundancyReport))
+    Config->RedudancyReportFile = Arg->getValue();
 
   if (ErrorCount)
     return;
Index: COFF/Options.td
===================================================================
--- COFF/Options.td
+++ COFF/Options.td
@@ -104,6 +104,7 @@
 // Flags for debugging
 def lldmap : F<"lldmap">;
 def lldmap_file : Joined<["/", "-"], "lldmap:">;
+def redundancyReport: Joined<["/", "-"], "redundancyReport:">;
 
 //==============================================================================
 // The flags below do nothing. They are defined only for link.exe compatibility.
Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -245,6 +245,7 @@
   } else if (SP == SP_NEW) {
     replaceBody<DefinedRegular>(S, F, N, IsCOMDAT, /*IsExternal*/ true, Sym, C);
   } else if (SP == SP_EXISTING && IsCOMDAT && C) {
+// XXX here?
     C->markDiscarded();
     // Discard associative chunks that we've parsed so far. No need to recurse
     // because an associative section cannot have children.
Index: COFF/Writer.cpp
===================================================================
--- COFF/Writer.cpp
+++ COFF/Writer.cpp
@@ -128,6 +128,7 @@
   void writeSections();
   void sortExceptionTable();
   void writeBuildId();
+  void writeRedundancyReport();
 
   llvm::Optional<coff_symbol16> createSymbol(Defined *D);
   size_t addEntryToStringTable(StringRef Str);
@@ -251,6 +252,7 @@
   }
 
   writeMapFile(OutputSections);
+  writeRedundancyReport();
 
   if (auto EC = Buffer->commit())
     fatal(EC, "failed to write the output file");
@@ -442,6 +444,7 @@
 
   // Don't write dead symbols or symbols in codeview sections to the symbol
   // table.
+  // XXX but do include them in stats
   if (!Def->isLive())
     return None;
   if (auto *D = dyn_cast<DefinedRegular>(Def))
@@ -825,6 +828,44 @@
   BuildId->DI->PDB70.Age = 1;
 }
 
+void Writer::writeRedundancyReport() {
+  if (Config->RedudancyReportFile.empty())
+    return;
+
+  FILE* f = fopen(Config->RedudancyReportFile.c_str(), "wb");
+
+  // First, bin chunks by name.
+  // XXX i think this misses stuff from .obj files never added to the link.
+  // probably fine.
+  struct Entry {
+    int total_size = 0;
+    int count = 0;
+  };
+  std::map<StringRef, Entry> Map;
+  for (Chunk *C : Symtab->getChunks()) {
+    auto *SC = dyn_cast<SectionChunk>(C);
+    if (!SC || SC->isLive())
+      continue;
+
+    Entry& e = Map[C->getDebugName()];
+    e.count++;
+    e.total_size += SC->getSize();
+  }
+
+  std::vector<std::pair<StringRef, Entry>> Entries(Map.begin(), Map.end());
+  std::sort(Entries.begin(), Entries.end(),
+            [](const std::pair<StringRef, Entry> &a,
+               const std::pair<StringRef, Entry> &b) {
+              return a.second.total_size > b.second.total_size;
+            });
+
+  for (const std::pair<StringRef, Entry>& E : Entries) {
+    fprintf(f, "%d\t%d\t%.*s\n", E.second.total_size, E.second.count,
+            (int)E.first.size(), E.first.data());
+  }
+  fclose(f);
+}
+
 OutputSection *Writer::findSection(StringRef Name) {
   for (OutputSection *Sec : OutputSections)
     if (Sec->getName() == Name)