Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -303,7 +303,7 @@
     // Thumb2 is the default for V7 on Darwin.
     //
     // FIXME: Thumb should just be another -target-feaure, not in the triple.
-    StringRef CPU = Triple.isOSBinFormatMachO()
+    std::string CPU = Triple.isOSBinFormatMachO()
       ? tools::arm::getARMCPUForMArch(Args, Triple)
       : tools::arm::getARMTargetCPU(Args, Triple);
     StringRef Suffix = 
Index: lib/Driver/Tools.h
===================================================================
--- lib/Driver/Tools.h
+++ lib/Driver/Tools.h
@@ -224,8 +224,8 @@
 } // end namespace hexagon.
 
 namespace arm {
-  StringRef getARMTargetCPU(const llvm::opt::ArgList &Args,
-                            const llvm::Triple &Triple);
+  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 char* getARMCPUForMArch(const llvm::opt::ArgList &Args,
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -767,7 +767,7 @@
   // the only function we have to check if a cpu is valid is
   // getLLVMArchSuffixForARM which also needs an architecture.
   if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
-    StringRef CPU = arm::getARMTargetCPU(Args, Triple);
+    std::string CPU = arm::getARMTargetCPU(Args, Triple);
     StringRef Arch = arm::getARMArch(Args, Triple);
     if (strcmp(arm::getLLVMArchSuffixForARM(CPU, Arch), "") == 0)
       D.Diag(diag::err_drv_clang_unsupported) << A->getAsString(Args);
@@ -5747,12 +5747,12 @@
 }
 
 /// getARMTargetCPU - Get the (LLVM) name of the ARM cpu we are targeting.
-StringRef arm::getARMTargetCPU(const ArgList &Args,
+std::string arm::getARMTargetCPU(const ArgList &Args,
                                const llvm::Triple &Triple) {
   // FIXME: Warn on inconsistent use of -mcpu and -march.
   // If we have -mcpu=, use that.
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
-    StringRef MCPU = A->getValue();
+    std::string MCPU = StringRef(A->getValue()).lower();
     // Handle -mcpu=native.
     if (MCPU == "native")
       return llvm::sys::getHostCPUName();
@@ -7254,7 +7254,7 @@
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:
   case llvm::Triple::thumbeb: {
-    std::string MArch(arm::getARMTargetCPU(Args, getToolChain().getTriple()));
+    std::string MArch = arm::getARMTargetCPU(Args, getToolChain().getTriple());
     CmdArgs.push_back(Args.MakeArgString("-mcpu=" + MArch));
     break;
   }
@@ -7601,7 +7601,7 @@
     // march from being picked in the absence of a cpu flag.
     Arg *A;
     if ((A = Args.getLastArg(options::OPT_mcpu_EQ)) &&
-      StringRef(A->getValue()) == "krait")
+      StringRef(A->getValue()).lower() == "krait")
         CmdArgs.push_back("-march=armv7-a");
     else
       Args.AddLastArg(CmdArgs, options::OPT_mcpu_EQ);
Index: test/Driver/arm-cortex-cpus.c
===================================================================
--- test/Driver/arm-cortex-cpus.c
+++ test/Driver/arm-cortex-cpus.c
@@ -392,3 +392,13 @@
 // RUN: %clang -target arm -mcpu=cortex-a57 -mbig-endian -mthumb -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-BE-CPUV8A-THUMB %s
 // RUN: %clang -target arm -mcpu=cortex-a72 -mbig-endian -mthumb -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-BE-CPUV8A-THUMB %s
 // CHECK-BE-CPUV8A-THUMB: "-cc1"{{.*}} "-triple" "thumbebv8-{{.*}}
+
+// ================== Check whether -mcpu accepts mixed-case values.
+// RUN: %clang -target arm-linux-gnueabi -mcpu=Cortex-a5 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
+// RUN: %clang -target arm-linux-gnueabi -mcpu=cortex-A7 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
+// RUN: %clang -target arm-linux-gnueabi -mcpu=CORTEX-a8 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
+// RUN: %clang -target arm-linux-gnueabi -mcpu=Cortex-A9 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
+// RUN: %clang -target arm-linux-gnueabi -mcpu=corteX-A12 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CASE-INSENSITIVE-CPUV7A %s
+// 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-{{.*}}
Index: test/Driver/krait-cpu.c
===================================================================
--- test/Driver/krait-cpu.c
+++ test/Driver/krait-cpu.c
@@ -1,3 +1,6 @@
 // ================== Check default Architecture on krait CPU
 // RUN: %clang -target arm-linux-gnueabi -mcpu=krait -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CPUV7A %s
+// ================== Check whether -mcpu accepts mixed-case values.
+// RUN: %clang -target arm-linux-gnueabi -mcpu=Krait -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CPUV7A %s
+// RUN: %clang -target arm-linux-gnueabi -mcpu=KRAIT -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CPUV7A %s
 // CHECK-CPUV7A: "-cc1"{{.*}} "-triple" "armv7-{{.*}}