Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -1848,7 +1848,8 @@
 getAArch64ArchFeaturesFromMarch(const Driver &D, StringRef March,
                                 const ArgList &Args,
                                 std::vector<const char *> &Features) {
-  std::pair<StringRef, StringRef> Split = March.split("+");
+  std::string MarchLowerCase = March.lower();
+  std::pair<StringRef, StringRef> Split = StringRef(MarchLowerCase).split("+");
 
   if (Split.first == "armv8-a" ||
       Split.first == "armv8a") {
Index: test/Driver/aarch64-cpus.c
===================================================================
--- test/Driver/aarch64-cpus.c
+++ test/Driver/aarch64-cpus.c
@@ -109,6 +109,13 @@
 // RUN: %clang -target aarch64 -mbig-endian -march=armv8.1-a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
 // RUN: %clang -target aarch64_be -mbig-endian -march=armv8.1a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
 // RUN: %clang -target aarch64_be -mbig-endian -march=armv8.1-a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// ================== Check whether -march accepts mixed-case values.
+// RUN: %clang -target aarch64_be -march=ARMV8.1A -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// RUN: %clang -target aarch64_be -march=ARMV8.1-A -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// RUN: %clang -target aarch64 -mbig-endian -march=Armv8.1A -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// RUN: %clang -target aarch64 -mbig-endian -march=Armv8.1-A -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// RUN: %clang -target aarch64_be -mbig-endian -march=ARMv8.1a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
+// RUN: %clang -target aarch64_be -mbig-endian -march=ARMV8.1-a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV81A-BE %s
 // GENERICV81A-BE: "-cc1"{{.*}} "-triple" "aarch64_be{{.*}}" "-target-cpu" "generic" "-target-feature" "+neon" "-target-feature" "+v8.1a"
 
 // ================== Check whether -mcpu accepts mixed-case values.