Index: lld/trunk/COFF/InputFiles.cpp
===================================================================
--- lld/trunk/COFF/InputFiles.cpp
+++ lld/trunk/COFF/InputFiles.cpp
@@ -339,8 +339,8 @@
 }
 
 void BitcodeFile::parse() {
-  Obj = check(lto::InputFile::create(
-      MemoryBufferRef(MB.getBuffer(), Saver.save(MB.getBufferIdentifier()))));
+  Obj = check(lto::InputFile::create(MemoryBufferRef(
+      MB.getBuffer(), Saver.save(ParentName + MB.getBufferIdentifier()))));
   for (const lto::InputFile::Symbol &ObjSym : Obj->symbols()) {
     StringRef SymName = Saver.save(ObjSym.getName());
     auto Flags = ObjSym.getFlags();
Index: lld/trunk/test/COFF/Inputs/bar.ll
===================================================================
--- lld/trunk/test/COFF/Inputs/bar.ll
+++ lld/trunk/test/COFF/Inputs/bar.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define void @bar() {
+  ret void
+}
Index: lld/trunk/test/COFF/thinlto-archives.ll
===================================================================
--- lld/trunk/test/COFF/thinlto-archives.ll
+++ lld/trunk/test/COFF/thinlto-archives.ll
@@ -0,0 +1,22 @@
+; RUN: rm -fr %T/thinlto-archives
+; RUN: mkdir %T/thinlto-archives %T/thinlto-archives/a %T/thinlto-archives/b
+; RUN: opt -thinlto-bc -o %T/thinlto-archives/main.obj %s
+; RUN: opt -thinlto-bc -o %T/thinlto-archives/a/bar.obj %S/Inputs/lto-dep.ll
+; RUN: opt -thinlto-bc -o %T/thinlto-archives/b/bar.obj %S/Inputs/bar.ll
+; RUN: llvm-ar crs %T/thinlto-archives/a.lib %T/thinlto-archives/a/bar.obj
+; RUN: llvm-ar crs %T/thinlto-archives/b.lib %T/thinlto-archives/b/bar.obj
+; RUN: lld-link /out:%T/thinlto-archives/main.exe -entry:main \
+; RUN:     -subsystem:console %T/thinlto-archives/main.obj \
+; RUN:     %T/thinlto-archives/a.lib %T/thinlto-archives/b.lib
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+declare void @bar()
+declare void @foo()
+
+define i32 @main() {
+  call void @foo()
+  call void @bar()
+  ret i32 0
+}
Index: lld/trunk/test/ELF/lto/archive-no-index.ll
===================================================================
--- lld/trunk/test/ELF/lto/archive-no-index.ll
+++ lld/trunk/test/ELF/lto/archive-no-index.ll
@@ -0,0 +1,39 @@
+; REQUIRES: x86
+; Tests that we suggest that LTO symbols missing from an archive index
+; may be the cause of undefined references, but only if we both
+; encountered an empty archive index and undefined references (to prevent
+; noisy false alarms).
+
+; RUN: rm -fr %T/archive-no-index
+; RUN: mkdir %T/archive-no-index
+; RUN: llvm-as %S/Inputs/archive.ll -o %T/archive-no-index/f.o
+; RUN: llvm-ar cr %T/archive-no-index/libf.a
+; RUN: llvm-ar qS %T/archive-no-index/libf.a %T/archive-no-index/f.o
+; RUN: llvm-as %s -o %t.o
+; RUN: not ld.lld -emain -m elf_x86_64 %t.o -o %t %T/archive-no-index/libf.a \
+; RUN:     2>&1 | FileCheck --check-prefix=NOTE %s
+
+; RUN: llvm-ar crs %T/archive-no-index/libfs.a %T/archive-no-index/f.o
+; RUN: ld.lld -emain -m elf_x86_64 %t.o -o %t %T/archive-no-index/libf.a \
+; RUN:     %T/archive-no-index/libfs.a
+
+; RUN: llvm-as %S/Inputs/archive-3.ll -o %T/archive-no-index/foo.o
+; RUN: llvm-ar crs %T/archive-no-index/libfoo.a %T/archive-no-index/foo.o
+; RUN: not ld.lld -emain -m elf_x86_64 %t.o -o %t %T/archive-no-index/libfoo.a \
+; RUN:     2>&1 | FileCheck --check-prefix=NO-NOTE %s
+
+; NOTE: undefined symbol 'f'
+; NOTE: archive listed no symbols
+
+; NO-NOTE: undefined symbol 'f'
+; NO-NOTE-NOT: archive listed no symbols
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @f()
+
+define i32 @main() {
+  call void @f()
+  ret i32 0
+}