diff --git a/llvm/test/tools/llvm-ar/mri-addlib.test b/llvm/test/tools/llvm-ar/mri-addlib.test
--- a/llvm/test/tools/llvm-ar/mri-addlib.test
+++ b/llvm/test/tools/llvm-ar/mri-addlib.test
@@ -1,34 +1,44 @@
 ## Test the ADDLIB MRI command.
 
-# RUN: rm -rf %t && mkdir -p %t
-# RUN: yaml2obj %s -o %t/f.o
-# RUN: llvm-ar r %t/f.a %t/f.o
+# RUN: rm -rf %t && split-file %s %t
+# RUN: cd %t
+# RUN: yaml2obj %s -o f.o
+# RUN: llvm-ar r f.a f.o
 
 ## Merge contents of archives.
-# RUN: echo "CREATE %t/addlib.a" > %t/addlib.mri
-# RUN: echo "ADDLIB %t/f.a" >> %t/addlib.mri
-# RUN: echo "SAVE" >> %t/addlib.mri
-# RUN: llvm-ar -M < %t/addlib.mri
-# RUN: llvm-nm --print-armap %t/addlib.a | FileCheck --check-prefix=SYMS %s
-# RUN: llvm-ar t %t/addlib.a | FileCheck --check-prefix=FILES %s
+# RUN: llvm-ar -M < add-lib.mri
+# RUN: llvm-nm --print-armap add-lib.a | FileCheck --check-prefix=SYMS %s
+# RUN: llvm-ar t add-lib.a | FileCheck --check-prefix=FILES %s
 
 # SYMS: f in {{.*}}
 # FILES: f.o
 
 ## ADDLIB with non-archive file.
-# RUN: echo "CREATE %t/badlib.a" > %t/badlib.mri
-# RUN: echo "ADDLIB %s" >> %t/badlib.mri
-# RUN: echo "SAVE" >> %t/badlib.mri
-# RUN: not llvm-ar -M < %t/badlib.mri 2>&1 | FileCheck --check-prefix=PARSE %s
-# RUN: not ls %t/badlib.a
+# RUN: not llvm-ar -M < bad-lib.mri 2>&1 | FileCheck --check-prefix=PARSE %s
+# RUN: not ls bad-lib.a
 
 # PARSE: error: script line 2: could not parse library
 
 ## No create command.
-# RUN: echo "ADDLIB %t/f.a" > %t/nocreate.mri
-# RUN: echo "SAVE" >> %t/nocreate.mri
-# RUN: not llvm-ar -M < %t/nocreate.mri
+# RUN: not llvm-ar -M < no-create.mri 2>&1 | FileCheck --check-prefix=NOCREATE %s
 
+# NOCREATE: error: script line 1: no output archive has been opened
+
+## ADDLIB with missing file.
+# RUN: not llvm-ar -M < missing.mri 2>&1 | FileCheck -DMSG=%errc_ENOENT %s --check-prefix=MISSING
+# RUN: not ls missing.a
+
+# MISSING: error: script line 2: could not open library missing-lib.a: [[MSG]]
+
+## ADD same lib twice.
+# RUN: llvm-ar -M < duplicate.mri
+# RUN: llvm-nm --print-armap duplicate.a | FileCheck --check-prefix=SYMS2 %s
+# RUN: llvm-ar t duplicate.a | FileCheck --check-prefix=FILES2 %s
+
+# SYMS2-COUNT-2: f in {{.*}}
+# FILES2-COUNT-2: f.o
+
+#--- f.yaml
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
@@ -43,3 +53,30 @@
       Binding: STB_GLOBAL
       Section: .text
 ...
+#--- add-lib.mri
+CREATE add-lib.a
+ADDLIB f.a
+SAVE
+
+#--- text.txt
+I AM NOT AN ARCHIVE
+
+#--- bad-lib.mri
+CREATE bad-lib.a
+ADDLIB text.txt
+SAVE
+
+#--- no-create.mri
+ADDLIB f.a
+SAVE
+
+#--- missing.mri
+CREATE missing.a
+ADDLIB missing-lib.a
+SAVE
+
+#--- duplicate.mri
+CREATE duplicate.a
+ADDLIB f.a
+ADDLIB f.a
+SAVE
diff --git a/llvm/test/tools/llvm-ar/mri-addmod.test b/llvm/test/tools/llvm-ar/mri-addmod.test
--- a/llvm/test/tools/llvm-ar/mri-addmod.test
+++ b/llvm/test/tools/llvm-ar/mri-addmod.test
@@ -1,16 +1,36 @@
 ## Test the ADDMOD MRI command.
 
-# RUN: rm -rf %t && mkdir -p %t
-# RUN: yaml2obj %s -o %t/f.o
+# RUN: rm -rf %t && split-file %s %t
+# RUN: cd %t
+# RUN: yaml2obj %s -o f.o
 
-# RUN: echo "CREATE %t/addmod.a" > %t/addmod.mri
-# RUN: echo "ADDMOD %t/f.o" >> %t/addmod.mri
-# RUN: echo "SAVE" >> %t/addmod.mri
-# RUN: llvm-ar -M < %t/addmod.mri
-# RUN: llvm-nm --print-armap %t/addmod.a | FileCheck %s
+# RUN: llvm-ar -M < add-mod.mri
+# RUN: llvm-nm --print-armap add-mod.a | FileCheck --check-prefix=SYMS %s
+# RUN: llvm-ar t add-mod.a | FileCheck --check-prefix=FILES %s
 
-# CHECK: f in f.o
+# SYMS: f in {{.*}}
+# FILES: f.o
 
+## No create command.
+# RUN: not llvm-ar -M < no-create.mri 2>&1 | FileCheck --check-prefix=NOCREATE %s
+
+# NOCREATE: error: script line 1: no output archive has been opened
+
+## ADDMOD with missing file.
+# RUN: not llvm-ar -M < missing.mri 2>&1 | FileCheck -DMSG=%errc_ENOENT %s --check-prefix=MISSING
+# RUN: not ls missing.a
+
+# MISSING: error: script line 2: missing.o: [[MSG]]
+
+## ADD same file twice.
+# RUN: llvm-ar -M < duplicate.mri
+# RUN: llvm-nm --print-armap duplicate.a | FileCheck --check-prefix=SYMS2 %s
+# RUN: llvm-ar t duplicate.a | FileCheck --check-prefix=FILES2 %s
+
+# SYMS2-COUNT-2: f in {{.*}}
+# FILES2-COUNT-2: f.o
+
+#--- f.yaml
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
@@ -25,3 +45,22 @@
       Binding: STB_GLOBAL
       Section: .text
 ...
+#--- add-mod.mri
+CREATE add-mod.a
+ADDMOD f.o
+SAVE
+
+#--- no-create.mri
+ADDMOD f.o
+SAVE
+
+#--- missing.mri
+CREATE missing.a
+ADDMOD missing.o
+SAVE
+
+#--- duplicate.mri
+CREATE duplicate.a
+ADDMOD f.o
+ADDMOD f.o
+SAVE
diff --git a/llvm/test/tools/llvm-ar/mri-create.test b/llvm/test/tools/llvm-ar/mri-create.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-ar/mri-create.test
@@ -0,0 +1,113 @@
+## Test the CREATE MRI command.
+
+# RUN: rm -rf %t && mkdir -p %t/path/ && split-file %s %t
+# RUN: cd %t
+
+# RUN: llvm-ar -M < create.mri
+# RUN: llvm-ar -M < thin.mri
+
+## Test use of CREATE with no archive name.
+# RUN: not llvm-ar -M < none.mri 2>&1 | FileCheck --check-prefix=NONE %s
+# RUN: not llvm-ar -M < thin-none.mri 2>&1 | FileCheck --check-prefix=NONE %s
+# RUN: not llvm-ar -M < none-add.mri 2>&1 | FileCheck --check-prefix=NONE %s
+# RUN: not llvm-ar -M < thin-none-add.mri 2>&1 | FileCheck --check-prefix=NONE %s
+
+# NONE: error: script line 1: missing archive name
+
+## Test use of paths with CREATE.
+# RUN: llvm-ar -M < path.mri
+# RUN: ls path/path.a
+# RUN: llvm-ar -M < thin-path.mri
+# RUN: ls path/thin-path.a
+
+## Test bad paths with CREATE.
+# RUN: not llvm-ar -M < bad.mri 2>&1 | FileCheck --check-prefix=BAD -DMSG=%errc_ENOENT %s
+# RUN: not llvm-ar -M < thin-bad.mri 2>&1 | FileCheck --check-prefix=BAD -DMSG=%errc_ENOENT %s
+# BAD: error: bad/bad.a: [[MSG]]
+
+## Test duplicate use of CREATE.
+# RUN: not llvm-ar -M < create2.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=2
+# RUN: not llvm-ar -M < thin2.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=2
+# RUN: not llvm-ar -M < mix1.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=2
+# RUN: not llvm-ar -M < mix2.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=2
+# RUN: not llvm-ar -M < save.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=3
+# RUN: not llvm-ar -M < thin-save.mri 2>&1 | FileCheck --check-prefix=MULTIPLE %s -DLINE=3
+
+# MULTIPLE: error: script line [[LINE]]: editing multiple archives not supported
+
+#--- create.mri
+CREATE create.a
+SAVE
+
+#--- thin.mri
+CREATETHIN thin.a
+SAVE thin.mri
+
+#--- none.mri
+CREATE
+SAVE
+
+#--- thin-none.mri
+CREATETHIN
+SAVE
+
+#--- foo.txt
+FOO
+
+#--- none-add.mri
+CREATE
+ADDMOD foo.txt
+SAVE
+
+#--- thin-none-add.mri
+CREATETHIN
+ADDMOD foo.txt
+SAVE
+
+#--- path.mri
+CREATE path/path.a
+SAVE
+
+#--- thin-path.mri
+CREATETHIN path/thin-path.a
+SAVE
+
+#--- bad.mri
+CREATE bad/bad.a
+SAVE
+
+#--- thin-bad.mri
+CREATETHIN bad/bad.a
+SAVE
+
+#--- create2.mri
+CREATE create1.a
+CREATE create2.a
+SAVE
+
+#--- thin2.mri
+CREATETHIN thin1.a
+CREATETHIN thin2.a
+SAVE
+
+#--- mix1.mri
+CREATE mix1.a
+CREATETHIN mixthin1.a
+SAVE
+
+#--- mix2.mri
+CREATETHIN mixthin2.a
+CREATE mix2.a
+SAVE
+
+#--- save.mri
+CREATE create1.a
+SAVE
+CREATE create2.a
+SAVE
+
+#--- thin-save.mri
+CREATETHIN create1.a
+SAVE
+CREATETHIN create2.a
+SAVE
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -1062,6 +1062,8 @@
 
     switch (Command) {
     case MRICommand::AddLib: {
+      if (!Create)
+        fail("no output archive has been opened");
       object::Archive &Lib = readLibrary(Rest);
       {
         Error Err = Error::success();
@@ -1072,6 +1074,8 @@
       break;
     }
     case MRICommand::AddMod:
+      if (!Create)
+        fail("no output archive has been opened");
       addMember(NewMembers, Rest);
       break;
     case MRICommand::CreateThin:
@@ -1084,6 +1088,8 @@
       if (Saved)
         fail("file already saved");
       ArchiveName = std::string(Rest);
+      if (ArchiveName.empty())
+        fail("missing archive name");
       break;
     case MRICommand::Delete: {
       llvm::erase_if(NewMembers, [=](NewArchiveMember &M) {