4 files changed, 31 insertions, 19 deletions

diff --git a/lld/ELF/LTO.cpp b/lld/ELF/LTO.cpp
index c97ff4d2476..4f641d647de 100644
--- a/lld/ELF/LTO.cpp
+++ b/lld/ELF/LTO.cpp
@@ -211,18 +211,24 @@ void BitcodeCompiler::add(BitcodeFile &F) {
   checkError(LTOObj->add(std::move(F.Obj), Resols));
 }
 
-static void createEmptyIndex(StringRef ModulePath) {
-  std::string Path = replaceThinLTOSuffix(getThinLTOOutputFile(ModulePath));
-  std::unique_ptr<raw_fd_ostream> OS = openFile(Path + ".thinlto.bc");
-  if (!OS)
-    return;
-
-  ModuleSummaryIndex M(/*HaveGVs*/ false);
-  M.setSkipModuleByDistributedBackend();
-  WriteIndexToFile(M, *OS);
-
-  if (Config->ThinLTOEmitImportsFiles)
-    openFile(Path + ".imports");
+// If LazyObjFile has not been added to link, emit empty index files.
+// This is needed because this is what GNU gold plugin does and we have a
+// distributed build system that depends on that behavior.
+void elf::thinLTOCreateEmptyIndexFiles() {
+  for (LazyObjFile *F : LazyObjFiles) {
+    if (F->AddedToLink || !isBitcode(F->MB))
+      continue;
+    std::string Path = replaceThinLTOSuffix(getThinLTOOutputFile(F->getName()));
+    std::unique_ptr<raw_fd_ostream> OS = openFile(Path + ".thinlto.bc");
+    if (!OS)
+      continue;
+
+    ModuleSummaryIndex M(/*HaveGVs*/ false);
+    M.setSkipModuleByDistributedBackend();
+    WriteIndexToFile(M, *OS);
+    if (Config->ThinLTOEmitImportsFiles)
+      openFile(Path + ".imports");
+  }
 }
 
 // Merge all the bitcode files we have seen, codegen the result
@@ -258,13 +264,8 @@ std::vector<InputFile *> BitcodeCompiler::compile() {
       openFile(Path + ".imports");
   }
 
-  // If LazyObjFile has not been added to link, emit empty index files.
-  // This is needed because this is what GNU gold plugin does and we have a
-  // distributed build system that depends on that behavior.
   if (Config->ThinLTOIndexOnly) {
-    for (LazyObjFile *F : LazyObjFiles)
-      if (!F->AddedToLink && isBitcode(F->MB))
-        createEmptyIndex(F->getName());
+    thinLTOCreateEmptyIndexFiles();
 
     if (!Config->LTOObjPath.empty())
       saveBuffer(Buf[0], Config->LTOObjPath);
diff --git a/lld/ELF/LTO.h b/lld/ELF/LTO.h
index 0f0b5bce718..1df1d2bbcfd 100644
--- a/lld/ELF/LTO.h
+++ b/lld/ELF/LTO.h
@@ -56,6 +56,8 @@ private:
   std::unique_ptr<llvm::raw_fd_ostream> IndexFile;
   llvm::DenseSet<StringRef> ThinIndices;
 };
+
+void thinLTOCreateEmptyIndexFiles();
 } // namespace elf
 } // namespace lld
 
diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp
index 2a511a26674..1b017b07f58 100644
--- a/lld/ELF/SymbolTable.cpp
+++ b/lld/ELF/SymbolTable.cpp
@@ -115,8 +115,11 @@ template <class ELFT> void SymbolTable::addFile(InputFile *File) {
 // Because all bitcode files that the program consists of are passed
 // to the compiler at once, it can do whole-program optimization.
 template <class ELFT> void SymbolTable::addCombinedLTOObject() {
-  if (BitcodeFiles.empty())
+  if (BitcodeFiles.empty()) {
+    if (Config->ThinLTOIndexOnly)
+      thinLTOCreateEmptyIndexFiles();
     return;
+  }
 
   // Compile bitcode files and replace bitcode symbols.
   LTO.reset(new BitcodeCompiler);
diff --git a/lld/test/ELF/lto/thinlto-index-only.ll b/lld/test/ELF/lto/thinlto-index-only.ll
index 6396057c9a3..3abc18e4875 100644
--- a/lld/test/ELF/lto/thinlto-index-only.ll
+++ b/lld/test/ELF/lto/thinlto-index-only.ll
@@ -38,6 +38,12 @@
 ; RUN: ls %t1.o.thinlto.bc
 ; RUN: ls %t1.o.imports
 
+; Ensure LLD generates an empty index for each bitcode file even if all bitcode files are lazy.
+; RUN: rm -f %t1.o.thinlto.bc
+; RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux-gnu /dev/null -o %tdummy.o
+; RUN: ld.lld --plugin-opt=thinlto-index-only -shared %tdummy.o --start-lib %t1.o --end-lib
+; RUN: ls %t1.o.thinlto.bc
+
 ; NM: T f
 
 ; The backend index for this module contains summaries from itself and