Index: lib/Driver/Tools.h
===================================================================
--- lib/Driver/Tools.h
+++ lib/Driver/Tools.h
@@ -226,8 +226,8 @@
 namespace arm {
   std::string getARMTargetCPU(const llvm::opt::ArgList &Args,
                               const llvm::Triple &Triple);
-  const StringRef getARMArch(const llvm::opt::ArgList &Args,
-                             const llvm::Triple &Triple);
+  const std::string getARMArch(const llvm::opt::ArgList &Args,
+                               const llvm::Triple &Triple);
   const char* getARMCPUForMArch(const llvm::opt::ArgList &Args,
                                 const llvm::Triple &Triple);
   const char* getLLVMArchSuffixForARM(StringRef CPU, StringRef Arch);
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -685,7 +685,7 @@
   // getARMArch is used here instead of just checking the -march value in order
   // to handle -march=native correctly.
   if (const Arg *A = Args.getLastArg(options::OPT_march_EQ)) {
-    StringRef Arch = arm::getARMArch(Args, Triple);
+    std::string Arch = arm::getARMArch(Args, Triple);
     if (llvm::ARMTargetParser::parseArch(Arch) == llvm::ARM::AK_INVALID)
       D.Diag(diag::err_drv_clang_unsupported) << A->getAsString(Args);
   }
@@ -695,7 +695,7 @@
   // getLLVMArchSuffixForARM which also needs an architecture.
   if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
     std::string CPU = arm::getARMTargetCPU(Args, Triple);
-    StringRef Arch = arm::getARMArch(Args, Triple);
+    std::string Arch = arm::getARMArch(Args, Triple);
     if (strcmp(arm::getLLVMArchSuffixForARM(CPU, Arch), "") == 0)
       D.Diag(diag::err_drv_clang_unsupported) << A->getAsString(Args);
   }
@@ -5628,9 +5628,9 @@
 }
 // Hexagon tools end.
 
-const StringRef arm::getARMArch(const ArgList &Args,
-                                const llvm::Triple &Triple) {
-  StringRef MArch;
+const std::string arm::getARMArch(const ArgList &Args,
+                                  const llvm::Triple &Triple) {
+  std::string MArch;
   if (Arg *A = Args.getLastArg(options::OPT_march_EQ)) {
     // Otherwise, if we have -march= choose the base CPU for that arch.
     MArch = A->getValue();
@@ -5638,6 +5638,7 @@
     // Otherwise, use the Arch from the triple.
     MArch = Triple.getArchName();
   }
+  MArch = StringRef(MArch).lower();
 
   // Handle -march=native.
   if (MArch == "native") {
@@ -5659,7 +5660,7 @@
 /// Get the (LLVM) name of the minimum ARM CPU for the arch we are targeting.
 const char *arm::getARMCPUForMArch(const ArgList &Args,
                                    const llvm::Triple &Triple) {
-  StringRef MArch = getARMArch(Args, Triple);
+  std::string MArch = getARMArch(Args, Triple);
   // getARMCPUForArch defaults to the triple if MArch is empty, but empty MArch
   // here means an -march=native that we can't handle, so instead return no CPU.
   if (MArch.empty())
Index: test/Driver/arm-cortex-cpus.c
===================================================================
--- test/Driver/arm-cortex-cpus.c
+++ test/Driver/arm-cortex-cpus.c
@@ -402,3 +402,12 @@
 // RUN: %clang -target arm-linux-gnueabi -mcpu=CorteX-a15 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
 // RUN: %clang -target arm-linux-gnueabi -mcpu=CorteX-A17 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
 // CHECK-CASE-INSENSITIVE-CPUV7A: "-cc1"{{.*}} "-triple" "armv7-{{.*}}
+
+// ================== Check whether -march accepts mixed-case values.
+// RUN: %clang -target arm -march=Armv5 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-V5 %s
+// RUN: %clang -target arm -march=ARMV5 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-V5 %s
+// CHECK-CASE-INSENSITIVE-V5: "-cc1"{{.*}} "-triple" "armv5-{{.*}} "-target-cpu" "arm10tdmi"
+
+// RUN: %clang -target arm -march=Armv6t2 -mthumb -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-V6T2-THUMB %s
+// RUN: %clang -target arm -march=ARMV6T2 -mthumb -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-V6T2-THUMB %s
+// CHECK-CASE-INSENSITIVE-V6T2-THUMB: "-cc1"{{.*}} "-triple" "thumbv6t2-{{.*}} "-target-cpu" "arm1156t2-s"