Index: llvm/include/llvm/Object/ArchiveWriter.h
===================================================================
--- llvm/include/llvm/Object/ArchiveWriter.h
+++ llvm/include/llvm/Object/ArchiveWriter.h
@@ -22,6 +22,7 @@
 
 struct NewArchiveMember {
   std::unique_ptr<MemoryBuffer> Buf;
+  StringRef MemberName;
   sys::TimePoint<std::chrono::seconds> ModTime;
   unsigned UID = 0, GID = 0, Perms = 0644;
 
Index: llvm/lib/Object/ArchiveWriter.cpp
===================================================================
--- llvm/lib/Object/ArchiveWriter.cpp
+++ llvm/lib/Object/ArchiveWriter.cpp
@@ -36,7 +36,8 @@
 using namespace llvm;
 
 NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
-    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)) {}
+    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
+      MemberName(BufRef.getBufferIdentifier()) {}
 
 Expected<NewArchiveMember>
 NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
@@ -48,6 +49,7 @@
   NewArchiveMember M;
   assert(M.IsNew == false);
   M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
+  M.MemberName = M.Buf->getBufferIdentifier();
   if (!Deterministic) {
     auto ModTimeOrErr = OldMember.getLastModified();
     if (!ModTimeOrErr)
@@ -97,6 +99,7 @@
   NewArchiveMember M;
   M.IsNew = true;
   M.Buf = std::move(*MemberBufferOrErr);
+  M.MemberName = M.Buf->getBufferIdentifier();
   if (!Deterministic) {
     M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
         Status.getLastModificationTime());
@@ -185,7 +188,7 @@
 }
 
 static bool useStringTable(bool Thin, StringRef Name) {
-  return Thin || Name.size() >= 16;
+  return Thin || Name.size() >= 16 || Name.contains('/');
 }
 
 static void
@@ -239,7 +242,7 @@
   unsigned StartOffset = 0;
   for (const NewArchiveMember &M : Members) {
     StringRef Path = M.Buf->getBufferIdentifier();
-    StringRef Name = sys::path::filename(Path);
+    StringRef Name = M.MemberName;
     if (!useStringTable(Thin, Name))
       continue;
     if (StartOffset == 0) {
@@ -423,9 +426,8 @@
     if (Kind == object::Archive::K_DARWIN)
       Padding = OffsetToAlignment(M.Buf->getBufferSize(), 8);
 
-    printMemberHeader(Out, Kind, Thin,
-                      sys::path::filename(M.Buf->getBufferIdentifier()),
-                      StringMapIndexIter, M.ModTime, M.UID, M.GID, M.Perms,
+    printMemberHeader(Out, Kind, Thin, M.MemberName, StringMapIndexIter,
+                      M.ModTime, M.UID, M.GID, M.Perms,
                       M.Buf->getBufferSize() + Padding);
 
     if (!Thin)
Index: llvm/test/LibDriver/use-paths.test
===================================================================
--- /dev/null
+++ llvm/test/LibDriver/use-paths.test
@@ -0,0 +1,24 @@
+llvm-lib should behave like "link.exe /lib" and use relative paths to describe
+archive members.
+
+First, get in a clean working directory.
+RUN: rm -rf %t && mkdir -p %t && cd %t
+
+Make foo/a.obj and foo/b.obj.
+RUN: mkdir foo
+RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o foo/a.obj %S/Inputs/a.s
+RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o foo/b.obj %S/Inputs/b.s
+
+RUN: llvm-lib -out:foo.lib foo/a.obj foo/b.obj
+RUN: llvm-ar t foo.lib | FileCheck %s
+
+FIXME: We should probably use backslashes on Windows to better match MSVC tools.
+CHECK: foo/a.obj
+CHECK: foo/b.obj
+
+Do it again with absolute paths and see that we get something.
+RUN: llvm-lib -out:foo.lib %t/foo/a.obj %t/foo/b.obj
+RUN: llvm-ar t foo.lib | FileCheck %s --check-prefix=ABS
+
+ABS: {{.*}}/foo/a.obj
+ABS: {{.*}}/foo/b.obj
Index: llvm/tools/llvm-ar/llvm-ar.cpp
===================================================================
--- llvm/tools/llvm-ar/llvm-ar.cpp
+++ llvm/tools/llvm-ar/llvm-ar.cpp
@@ -473,6 +473,10 @@
   Expected<NewArchiveMember> NMOrErr =
       NewArchiveMember::getFile(FileName, Deterministic);
   failIfError(NMOrErr.takeError(), FileName);
+
+  // Use the basename of the object path for the member name.
+  NMOrErr->MemberName = sys::path::filename(NMOrErr->MemberName);
+
   if (Pos == -1)
     Members.push_back(std::move(*NMOrErr));
   else