Index: llvm/test/tools/llvm-ar/mri-create-overwrite.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-ar/mri-create-overwrite.test
@@ -0,0 +1,84 @@
+## Show that CREATE/CREATETHIN overwrite existing files appropriately.
+
+# RUN: touch %t/1.txt
+# RUN: touch %t/2.txt
+
+# ARCH: !<arch>
+# THIN: !<thin>
+# ONE:  1.txt
+# TWO:  2.txt
+
+## Show that an existing file that is not an archive is overwritten by CREATE.
+# RUN: rm -f %t/test.a
+# RUN: touch %t/test.a
+# RUN: echo "CREATE %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/1.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=ARCH,ONE
+
+## Show that an existing file that is not an archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/test.a
+# RUN: touch %t/test.a
+# RUN: echo "CREATETHIN %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/1.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=THIN,ONE
+
+## Show that an existing regular archive is overwritten by CREATE.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar cr %t/test.a  %t/1.txt
+# RUN: echo "CREATE %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: llvm-ar tv %t/test.a
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=ARCH,TWO --implicit-check-not=1.txt
+
+## Show that an existing regular archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar cr %t/test.a  %t/1.txt
+# RUN: echo "CREATETHIN %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=THIN,TWO --implicit-check-not=1.txt
+
+## Show that an existing thin archive is overwritten by CREATE.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar crT %t/test.a  %t/1.txt
+# RUN: echo "CREATE %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=ARCH,TWO --implicit-check-not=1.txt
+
+## Show that an existing thin archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar crT %t/test.a  %t/1.txt
+# RUN: echo "CREATETHIN %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=THIN,TWO --implicit-check-not=1.txt
+
+## Show that the output is not overwritten without a SAVE.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar crT %t/test.a  %t/1.txt
+# RUN: echo "CREATE %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=THIN,ONE --implicit-check-not=2.txt
+
+## Show that only the last mentioned file is overwritten.
+# RUN: rm -f %t/test.a
+# RUN: llvm-ar crT %t/test.a  %t/1.txt
+# RUN: echo "CREATE %t/test.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/1.txt" >> %t/test.mri
+# RUN: echo "CREATETHIN %t/last.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+# RUN: FileCheck --input-file=%t/test.a %s --check-prefixes=THIN,ONE --implicit-check-not=2.txt
+# RUN: FileCheck --input-file=%t/last.a %s --check-prefixes=THIN,TWO --implicit-check-not=1.txt
Index: llvm/tools/llvm-ar/llvm-ar.cpp
===================================================================
--- llvm/tools/llvm-ar/llvm-ar.cpp
+++ llvm/tools/llvm-ar/llvm-ar.cpp
@@ -1052,7 +1052,8 @@
     }
   }
 
-  performOperation(Operation, nullptr, nullptr, NewMembers);
+  performOperation(Operation, /*OldArchive*/ nullptr, /*OldArchiveBuf*/ nullptr,
+                   NewMembers);
   return 0;
 }
 
@@ -1134,7 +1135,8 @@
 
   // Nothing to do if not saved.
   if (Saved)
-    performOperation(ReplaceOrInsert, &NewMembers);
+    performOperation(ReplaceOrInsert, /*OldArchive*/ nullptr,
+                     /*OldArchiveBuf*/ nullptr, &NewMembers);
   exit(0);
 }