diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -1737,21 +1737,6 @@
   if (!MultiArg)
     NumOccurrences++; // Increment the number of times we have been seen
 
-  switch (getNumOccurrencesFlag()) {
-  case Optional:
-    if (NumOccurrences > 1)
-      return error("may only occur zero or one times!", ArgName);
-    break;
-  case Required:
-    if (NumOccurrences > 1)
-      return error("must occur exactly one time!", ArgName);
-    LLVM_FALLTHROUGH;
-  case OneOrMore:
-  case ZeroOrMore:
-  case ConsumeAfter:
-    break;
-  }
-
   return handleOccurrence(pos, ArgName, Value);
 }
 
diff --git a/llvm/test/tools/llvm-libtool-darwin/create-static-lib.test b/llvm/test/tools/llvm-libtool-darwin/create-static-lib.test
--- a/llvm/test/tools/llvm-libtool-darwin/create-static-lib.test
+++ b/llvm/test/tools/llvm-libtool-darwin/create-static-lib.test
@@ -4,8 +4,10 @@
 # RUN: yaml2obj %S/Inputs/input2.yaml -o %t-input2.o
 # RUN: llvm-as %S/Inputs/x86_64-osx.ll -o %t-x86_64.bc
 
-# RUN: rm -rf %t.lib
+# RUN: rm -rf %t.lib %t2.lib
 # RUN: llvm-libtool-darwin -static -o %t.lib %t-input1.o %t-input2.o %t-x86_64.bc
+# RUN: llvm-libtool-darwin -static -o %t2.lib -o %t.lib %t-input1.o %t-input2.o %t-x86_64.bc
+# RUN: not ls %t2.lib
 
 ## Check that binaries are present:
 # RUN: llvm-ar t %t.lib | \
diff --git a/llvm/test/tools/llvm-libtool-darwin/deterministic-library.test b/llvm/test/tools/llvm-libtool-darwin/deterministic-library.test
--- a/llvm/test/tools/llvm-libtool-darwin/deterministic-library.test
+++ b/llvm/test/tools/llvm-libtool-darwin/deterministic-library.test
@@ -24,16 +24,12 @@
 # CHECK-NONDETERMINISTIC:  {{[[:space:]]1995[[:space:]]}}
 
 ## D Flag specified more than once:
-# RUN: not llvm-libtool-darwin -static -o %t.lib %t-input1.o -D -D 2>&1 | \
-# RUN:   FileCheck %s --check-prefix=CHECK-ERROR-D
-
-# CHECK-ERROR-D: for the -D option: may only occur zero or one times!
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-input1.o -D -D 2>&1 |& count 0
+# RUN: env TZ=GMT llvm-ar tv %t.lib | FileCheck %s --check-prefix=CHECK-DETERMINISTIC
 
 ## U Flag specified more than once:
-# RUN: not llvm-libtool-darwin -static -o %t.lib %t-input1.o -U -U 2>&1 | \
-# RUN:   FileCheck %s --check-prefix=CHECK-ERROR-U
-
-# CHECK-ERROR-U: for the -U option: may only occur zero or one times!
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-input1.o -U -U 2>&1 |& count 0
+# RUN: env TZ=GMT llvm-ar tv %t.lib | FileCheck %s --check-prefix=CHECK-NONDETERMINISTIC
 
 ## Both D and U flags specified:
 # RUN: not llvm-libtool-darwin -static -o %t.lib %t-input1.o -D -U 2>&1 | \
diff --git a/llvm/test/tools/llvm-libtool-darwin/filelist.test b/llvm/test/tools/llvm-libtool-darwin/filelist.test
--- a/llvm/test/tools/llvm-libtool-darwin/filelist.test
+++ b/llvm/test/tools/llvm-libtool-darwin/filelist.test
@@ -30,10 +30,10 @@
 
 # RUN: rm -rf %t/dirname && mkdir -p %t/dirname
 # RUN: yaml2obj %S/Inputs/input1.yaml -o %t/dirname/%basename_t.tmp-input1.o
-# RUN: echo %basename_t.tmp-input1.o > %t.files.txt
+# RUN: echo %basename_t.tmp-input1.o > %t.files2.txt
 
 ## Passing in dirname:
-# RUN: llvm-libtool-darwin -static -o %t.lib -filelist %t.files.txt,%t/dirname
+# RUN: llvm-libtool-darwin -static -o %t.lib -filelist %t.files2.txt,%t/dirname
 # RUN: llvm-ar t %t.lib | \
 # RUN:   FileCheck %s --check-prefix=DIRNAME-NAMES --implicit-check-not={{.}} -DPREFIX=%basename_t.tmp
 # RUN: llvm-nm --print-armap %t.lib | \
@@ -46,7 +46,7 @@
 # DIRNAME-SYMBOLS-EMPTY:
 
 ## Passing both -filelist option and object file as input:
-# RUN: llvm-libtool-darwin -static -o %t.lib -filelist %t.files.txt,%t/dirname %t-input2.o
+# RUN: llvm-libtool-darwin -static -o %t.lib -filelist %t.files2.txt,%t/dirname %t-input2.o
 # RUN: llvm-ar t %t.lib | \
 # RUN:   FileCheck %s --check-prefix=REVERSE-NAMES --implicit-check-not={{.}} -DPREFIX=%basename_t.tmp
 # RUN: llvm-nm --print-armap %t.lib | \
@@ -106,7 +106,6 @@
 
 ## Filelist option specified more than once:
 # RUN: touch %t.list1.txt and %t.list2.txt
-# RUN: not llvm-libtool-darwin -static -o %t.lib -filelist %t.list1.txt -filelist %t.list2.txt 2>&1 | \
-# RUN:   FileCheck %s --check-prefix=DUPLICATE-ERROR
-
-# DUPLICATE-ERROR: for the --filelist option: may only occur zero or one times!
+# RUN: llvm-libtool-darwin -static -o %t.lib -filelist %t.empty-list -filelist %t.files.txt 2>&1
+# RUN: llvm-ar t %t.lib | \
+# RUN:   FileCheck %s --check-prefix=CHECK-NAMES --implicit-check-not={{.}} -DPREFIX=%basename_t.tmp
diff --git a/llvm/test/tools/llvm-libtool-darwin/invalid-input-output-args.test b/llvm/test/tools/llvm-libtool-darwin/invalid-input-output-args.test
--- a/llvm/test/tools/llvm-libtool-darwin/invalid-input-output-args.test
+++ b/llvm/test/tools/llvm-libtool-darwin/invalid-input-output-args.test
@@ -18,12 +18,6 @@
 
 # MISSING: for the -o option: requires a value!
 
-## Passing in two output files:
-# RUN: not llvm-libtool-darwin -static %t.input -o %t.lib1 -o %t.lib2 2>&1 | \
-# RUN:   FileCheck %s --check-prefix=DOUBLE-OUTPUT
-
-# DOUBLE-OUTPUT: for the -o option: may only occur zero or one times!
-
 ## Input file not found:
 # RUN: not llvm-libtool-darwin -static -o %t.lib %t.missing 2>&1 | \
 # RUN:   FileCheck %s --check-prefix=NO-FILE -DFILE=%t.missing -DMSG=%errc_ENOENT
diff --git a/llvm/unittests/Support/CommandLineTest.cpp b/llvm/unittests/Support/CommandLineTest.cpp
--- a/llvm/unittests/Support/CommandLineTest.cpp
+++ b/llvm/unittests/Support/CommandLineTest.cpp
@@ -420,6 +420,14 @@
       << "Hid default option that should be visable.";
 }
 
+TEST(CommandLineTest, SetMultiValues) {
+  StackOption<int> Option("option");
+  const char *args[] = {"prog", "-option=1", "-option=2"};
+  EXPECT_TRUE(cl::ParseCommandLineOptions(array_lengthof(args), args,
+                                          StringRef(), &llvm::nulls()));
+  EXPECT_EQ(Option, 2);
+}
+
 TEST(CommandLineTest, SetValueInSubcategories) {
   cl::ResetCommandLineParser();
 
diff --git a/mlir/test/Pass/pipeline-options-parsing.mlir b/mlir/test/Pass/pipeline-options-parsing.mlir
--- a/mlir/test/Pass/pipeline-options-parsing.mlir
+++ b/mlir/test/Pass/pipeline-options-parsing.mlir
@@ -2,7 +2,7 @@
 // RUN: not mlir-opt %s -pass-pipeline='builtin.module(test-module-pass{test-option=3})' 2>&1 | FileCheck --check-prefix=CHECK_ERROR_2 %s
 // RUN: not mlir-opt %s -pass-pipeline='builtin.module(builtin.func(test-options-pass{list=3}), test-module-pass{invalid-option=3})' 2>&1 | FileCheck --check-prefix=CHECK_ERROR_3 %s
 // RUN: not mlir-opt %s -pass-pipeline='test-options-pass{list=3 list=notaninteger}' 2>&1 | FileCheck --check-prefix=CHECK_ERROR_4 %s
-// RUN: not mlir-opt %s -pass-pipeline='builtin.func(test-options-pass{list=1,2,3,4 list=5 string=value1 string=value2})' 2>&1 | FileCheck --check-prefix=CHECK_ERROR_5 %s
+// RUN: mlir-opt %s -pass-pipeline='builtin.func(test-options-pass{list=1,2,3,4 list=5 string=value1 string=value2})'
 // RUN: mlir-opt %s -verify-each=false -pass-pipeline='builtin.func(test-options-pass{string-list=a list=1,2,3,4 string-list=b,c list=5 string-list=d string=nested_pipeline{arg1=10 arg2=" {} " arg3=true}})' -test-dump-pipeline 2>&1 | FileCheck --check-prefix=CHECK_1 %s
 // RUN: mlir-opt %s -verify-each=false -test-options-pass-pipeline='list=1 string-list=a,b' -test-dump-pipeline 2>&1 | FileCheck --check-prefix=CHECK_2 %s
 // RUN: mlir-opt %s -verify-each=false -pass-pipeline='builtin.module(builtin.func(test-options-pass{list=3}), builtin.func(test-options-pass{list=1,2,3,4}))' -test-dump-pipeline 2>&1 | FileCheck --check-prefix=CHECK_3 %s
@@ -11,7 +11,6 @@
 // CHECK_ERROR_2: no such option test-option
 // CHECK_ERROR_3: no such option invalid-option
 // CHECK_ERROR_4: 'notaninteger' value invalid for integer argument
-// CHECK_ERROR_5: string option: may only occur zero or one times
 
 // CHECK_1: test-options-pass{list=1,2,3,4,5 string=nested_pipeline{arg1=10 arg2=" {} " arg3=true} string-list=a,b,c,d}
 // CHECK_2: test-options-pass{list=1 string= string-list=a,b}