Index: test/tools/llvm-ar/mri-thin-archive.test
===================================================================
--- test/tools/llvm-ar/mri-thin-archive.test
+++ test/tools/llvm-ar/mri-thin-archive.test
@@ -0,0 +1,23 @@
+RUN: rm -rf %t && mkdir -p %t/addlib/
+
+RUN: yaml2obj %S/Inputs/elf.yaml -o %t/elf.o
+RUN: cp %t/elf.o %t/addlib/elf.o
+RUN: cp %t/elf.o %t/delete.o
+
+RUN: cd %t && llvm-ar rTc addlib/addlib.ar addlib/elf.o
+
+RUN: echo "createthin %t/archive.ar" > %t/mri.script
+RUN: echo "addmod elf.o" >> %t/mri.script
+RUN: echo "addlib addlib/addlib.ar" >> %t/mri.script
+RUN: echo "addmod delete.o" >> %t/mri.script
+RUN: echo "delete delete.o" >> %t/mri.script
+RUN: echo "save" >> %t/mri.script
+RUN: echo "end" >> %t/mri.script
+
+RUN: cd %t && llvm-ar -M < mri.script
+RUN: FileCheck -input-file=%t/archive.ar %s
+
+CHECK: !<thin>
+CHECK: elf.o
+CHECK-NEXT: addlib/elf.o/
+CHECK-NOT: delete.o
Index: tools/llvm-ar/llvm-ar.cpp
===================================================================
--- tools/llvm-ar/llvm-ar.cpp
+++ tools/llvm-ar/llvm-ar.cpp
@@ -952,7 +952,7 @@
 }
 
 static void runMRIScript() {
-  enum class MRICommand { AddLib, AddMod, Create, Delete, Save, End, Invalid };
+  enum class MRICommand { AddLib, AddMod, Create, CreateThin, Delete, Save, End, Invalid };
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> Buf = MemoryBuffer::getSTDIN();
   failIfError(Buf.getError());
@@ -976,6 +976,7 @@
                        .Case("addlib", MRICommand::AddLib)
                        .Case("addmod", MRICommand::AddMod)
                        .Case("create", MRICommand::Create)
+                       .Case("createthin", MRICommand::CreateThin)
                        .Case("delete", MRICommand::Delete)
                        .Case("save", MRICommand::Save)
                        .Case("end", MRICommand::End)
@@ -995,6 +996,9 @@
     case MRICommand::AddMod:
       addMember(NewMembers, Rest);
       break;
+    case MRICommand::CreateThin:
+      Thin = true;
+      LLVM_FALLTHROUGH;
     case MRICommand::Create:
       Create = true;
       if (!ArchiveName.empty())