Index: lld/ELF/LTO.h
===================================================================
--- lld/ELF/LTO.h
+++ lld/ELF/LTO.h
@@ -55,6 +55,7 @@
   std::vector<SmallString<0>> Buff;
   std::vector<std::unique_ptr<MemoryBuffer>> Files;
   llvm::DenseSet<StringRef> UsedStartStop;
+  llvm::StringMap<bool> ObjectToIndexFileState;
   std::unique_ptr<llvm::raw_fd_ostream> LinkedObjects;
 };
 } // namespace elf
Index: lld/ELF/LTO.cpp
===================================================================
--- lld/ELF/LTO.cpp
+++ lld/ELF/LTO.cpp
@@ -115,9 +115,11 @@
 }
 
 // Creates instance of LTO.
+// OnIndexWrite is callback to let caller know when LTO writes index files.
 // LinkedObjectsFile is an output stream to write the list of object files for
 // the final ThinLTO linking. Can be nullptr.
-static std::unique_ptr<lto::LTO> createLTO(raw_fd_ostream *LinkedObjectsFile) {
+static std::unique_ptr<lto::LTO> createLTO(lto::IndexWriteCallback OnIndexWrite,
+                                           raw_fd_ostream *LinkedObjectsFile) {
   lto::Config Conf;
 
   // LLD supports the new relocations.
@@ -159,8 +161,8 @@
   if (Config->ThinLTOIndexOnly) {
     std::string OldPrefix, NewPrefix;
     std::tie(OldPrefix, NewPrefix) = Config->ThinLTOPrefixReplace.split(';');
-    Backend = lto::createWriteIndexesThinBackend(OldPrefix, NewPrefix, true,
-                                                 LinkedObjectsFile, nullptr);
+    Backend = lto::createWriteIndexesThinBackend(
+        OldPrefix, NewPrefix, true, LinkedObjectsFile, OnIndexWrite);
   }
 
   Conf.SampleProfile = Config->LTOSampleProfile;
@@ -173,7 +175,11 @@
 
 BitcodeCompiler::BitcodeCompiler() {
   LinkedObjects = createLinkedObjectsFile();
-  LTOObj = createLTO(LinkedObjects.get());
+  LTOObj = createLTO(
+      [&](const std::string &Identifier) {
+        ObjectToIndexFileState[Identifier] = true;
+      },
+      LinkedObjects.get());
   for (Symbol *Sym : Symtab->getSymbols()) {
     StringRef Name = Sym->getName();
     for (StringRef Prefix : {"__start_", "__stop_"})
@@ -192,13 +198,8 @@
 void BitcodeCompiler::add(BitcodeFile &F) {
   lto::InputFile &Obj = *F.Obj;
 
-  std::string OldPrefix, NewPrefix;
-  std::tie(OldPrefix, NewPrefix) = Config->ThinLTOPrefixReplace.split(';');
-
-  // Create the empty files which, if indexed, will be overwritten later.
   if (Config->ThinLTOIndexOnly)
-    writeEmptyDistributedBuildOutputs(Obj.getName(), OldPrefix, NewPrefix,
-                                      false);
+    ObjectToIndexFileState.insert({Obj.getName(), false});
 
   unsigned SymNum = 0;
   std::vector<Symbol *> Syms = F.getSymbols();
@@ -281,6 +282,25 @@
       },
       Cache));
 
+  // Emit empty index files for non-indexed files
+  if (Config->ThinLTOIndexOnly) {
+    std::string OldPrefix, NewPrefix;
+    std::tie(OldPrefix, NewPrefix) = Config->ThinLTOPrefixReplace.split(';');
+    for (auto &Identifier : ObjectToIndexFileState)
+      if (!Identifier.getValue())
+        writeEmptyDistributedBuildOutputs(Identifier.getKey(), OldPrefix,
+                                          NewPrefix, /* SkipModule */ false);
+  }
+
+  // ThinLTO with index only option is required to generate only the index
+  // files. After that, we exit from linker and ThinLTO backend runs in a
+  // distributed environment.
+  if (Config->ThinLTOIndexOnly) {
+    if (Config->SaveTemps)
+      saveBuffer(Buff[0], Config->OutputFile + ".lto.o");
+    exit(0);
+  }
+
   if (!Config->ThinLTOCacheDir.empty())
     pruneCache(Config->ThinLTOCacheDir, Config->ThinLTOCachePolicy);
 
@@ -297,12 +317,6 @@
     Ret.push_back(Obj);
   }
 
-  // ThinLTO with index only option is required to generate only the index
-  // files. After that, we exit from linker and ThinLTO backend runs in a
-  // distributed environment.
-  if (Config->ThinLTOIndexOnly)
-    exit(0);
-
   for (std::unique_ptr<MemoryBuffer> &File : Files)
     if (File)
       Ret.push_back(createObjectFile(*File));
Index: lld/test/ELF/lto/thinlto.ll
===================================================================
--- lld/test/ELF/lto/thinlto.ll
+++ lld/test/ELF/lto/thinlto.ll
@@ -42,6 +42,11 @@
 ; RUN: not ls %t2.o.thinlto.bc
 ; RUN: not ls %t4.o.thinlto.bc
 
+; Ensure lld generates one regular LTO file via splitting for ThinLTO builds
+; RUN: rm -f %t.lto.o
+; RUN: ld.lld -save-temps --plugin-opt=thinlto-index-only -shared %t.o %t2.o -o %t
+; RUN: llvm-readobj -h %t.lto.o | FileCheck %s --check-prefix=FORMAT
+
 ; First force single-threaded mode
 ; RUN: rm -f %t.lto.o %t1.lto.o
 ; RUN: ld.lld -save-temps --thinlto-jobs=1 -shared %t.o %t2.o -o %t