Index: llvm/test/tools/llvm-ar/mri-create-overwrite.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-ar/mri-create-overwrite.test
@@ -0,0 +1,100 @@
+## Show that CREATE/CREATETHIN overwrite existing files appropriately.
+
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: touch %t/archive.a
+# RUN: touch %t/1.txt
+# RUN: touch %t/2.txt
+
+## Show that an existing file that is not an archive is overwritten by CREATE.
+# RUN: echo "CREATE %t/archive.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: llvm-ar tv %t/archive.a | \
+# RUN:   FileCheck %s --check-prefix=CREATE
+CREATE: 1.txt
+
+## Show that an existing file that is not an archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/archive.a
+# RUN: touch %t/archive.a
+# RUN: echo "CREATETHIN %t/archive.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: llvm-ar tv %t/archive.a | \
+# RUN:   FileCheck %s --check-prefix=CREATETHIN
+CREATETHIN: 1.txt
+
+## Show that an existing full archive is overwritten by CREATE.
+# RUN: rm -f %t/archive.a
+# RUN: llvm-ar cr %t/archive.a  %t/1.txt
+# RUN: echo "CREATE %t/archive.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/archive.a
+# RUN: FileCheck -input-file=%t/archive.a %s --check-prefix=FULL_CREATE --implicit-check-not=1.txt
+FULL_CREATE: !<arch>
+FULL_CREATE: 2.txt
+
+## Show that an existing full archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/archive.a
+# RUN: llvm-ar cr %t/archive.a  %t/1.txt
+# RUN: echo "CREATETHIN %t/archive.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/archive.a
+# RUN: FileCheck -input-file=%t/archive.a %s --check-prefix=FULL_CREATETHIN --implicit-check-not=1.txt
+FULL_CREATETHIN: !<thin>
+FULL_CREATETHIN: 2.txt
+
+## Show that an existing thin archive is overwritten by CREATE.
+# RUN: rm -f %t/archive.a
+# RUN: llvm-ar crT %t/archive.a  %t/1.txt
+# RUN: echo "CREATE %t/archive.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/archive.a
+# RUN: FileCheck -input-file=%t/archive.a %s --check-prefix=THIN_CREATE --implicit-check-not=1.txt
+THIN_CREATE: !<arch>
+THIN_CREATE: 2.txt
+
+## Show that an existing thin archive is overwritten by CREATETHIN.
+# RUN: rm -f %t/archive.a
+# RUN: llvm-ar crT %t/archive.a  %t/1.txt
+# RUN: echo "CREATETHIN %t/archive.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/archive.a
+# RUN: FileCheck -input-file=%t/archive.a %s --check-prefix=THIN_CREATETHIN --implicit-check-not=1.txt
+THIN_CREATETHIN: !<thin>
+THIN_CREATETHIN: 2.txt
+
+## Make archive read-only.
+# RUN: chmod 444 %t/archive.a
+
+## Show that the output is not overwritten without a SAVE.
+# RUN: echo "CREATE %t/archive.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/2.txt" >> %t/test.mri
+# RUN: llvm-ar -M < %t/test.mri
+
+## Show that a read-only file is not overwritten.
+# RUN: echo "SAVE" >> %t/test.mri
+# RUN: not llvm-ar -M < %t/test.mri 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=ERROR -DFILE=%t/archive.a
+# ERROR: error: [[FILE]]: permission denied
+
+## Show that only the last mentioned file is overwritten.
+# RUN: echo "CREATE %t/archive.a" > %t/test.mri
+# RUN: echo "ADDMOD %t/1.txt" >> %t/test.mri
+# RUN: echo "CREATETHIN %t/second.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/second.a | \
+# RUN:  FileCheck %s --check-prefix=SECOND
+SECOND: 2.txt
+
Index: llvm/tools/llvm-ar/llvm-ar.cpp
===================================================================
--- llvm/tools/llvm-ar/llvm-ar.cpp
+++ llvm/tools/llvm-ar/llvm-ar.cpp
@@ -1134,7 +1134,7 @@
 
   // Nothing to do if not saved.
   if (Saved)
-    performOperation(ReplaceOrInsert, &NewMembers);
+    performOperation(ReplaceOrInsert, nullptr, nullptr, &NewMembers);
   exit(0);
 }