Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -99,6 +99,7 @@
   std::vector<SymbolVersion> VersionScriptLocals;
   std::vector<uint8_t> BuildIdVector;
   bool AllowMultipleDefinition;
+  bool ArchiveWithoutSymbolsWarned = false;
   bool AsNeeded = false;
   bool Bsymbolic;
   bool BsymbolicFunctions;
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -187,7 +187,7 @@
     // we'll handle it as if it had a symbol table.
     if (!File->hasSymbolTable()) {
       for (MemoryBufferRef MB : getArchiveMembers(MBRef))
-        Files.push_back(make<LazyObjectFile>(MB));
+        Files.push_back(make<LazyObjectFile>(MB, MBRef.getBufferIdentifier()));
       return;
     }
 
@@ -215,7 +215,7 @@
     return;
   default:
     if (InLib)
-      Files.push_back(make<LazyObjectFile>(MBRef));
+      Files.push_back(make<LazyObjectFile>(MBRef, ""));
     else
       Files.push_back(createObjectFile(MBRef));
   }
Index: ELF/InputFiles.h
===================================================================
--- ELF/InputFiles.h
+++ ELF/InputFiles.h
@@ -219,7 +219,10 @@
 // archive file semantics.
 class LazyObjectFile : public InputFile {
 public:
-  explicit LazyObjectFile(MemoryBufferRef M) : InputFile(LazyObjectKind, M) {}
+  explicit LazyObjectFile(MemoryBufferRef M, StringRef ArchiveName)
+      : InputFile(LazyObjectKind, M) {
+    this->ArchiveName = ArchiveName;
+  }
 
   static bool classof(const InputFile *F) {
     return F->kind() == LazyObjectKind;
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -981,6 +981,16 @@
   MemoryBufferRef MBRef = getBuffer();
   if (MBRef.getBuffer().empty())
     return nullptr;
+  if (!ArchiveName.empty() && !Config->ArchiveWithoutSymbolsWarned) {
+    warn("At least the " + ArchiveName +
+         " archive listed no symbols in its index. This can happen when "
+         "creating archives with a version of ar that does not understand the "
+         "object files in the archive. For example, if you are using LLVM "
+         "bitcode objects (such as created by -flto), you may need to use "
+         "llvm-ar or GNU ar with a plugin.");
+    // Set to true so that we print the message only once.
+    Config->ArchiveWithoutSymbolsWarned = true;
+  }
   return createObjectFile(MBRef);
 }
 
Index: test/ELF/lto/archive-no-index.ll
===================================================================
--- test/ELF/lto/archive-no-index.ll
+++ test/ELF/lto/archive-no-index.ll
@@ -11,9 +11,11 @@
 ; RUN: llvm-ar crS %t1.a %t2.o
 ; RUN: llvm-ar crs %t2.a %t2.o
 
-; RUN: ld.lld -o %t -emain -m elf_x86_64 %t1.o %t1.a
+; RUN: ld.lld -o %t -emain -m elf_x86_64 %t1.o %t1.a 2>&1 | FileCheck %s
 ; RUN: ld.lld -o %t -emain -m elf_x86_64 %t1.o %t2.a
 
+; CHECK: warning: At least the {{.*}}archive-no-index.ll.tmp1.a archive listed no symbols in its index. This can happen when creating archives with a version of ar that does not understand the object files in the archive. For example, if you are using LLVM bitcode objects (such as created by -flto), you may need to use llvm-ar or GNU ar with a plugin.
+
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"