Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -126,7 +126,7 @@
 }
 
 static const char *GetArmArchForMCpu(StringRef Value) {
-  return llvm::StringSwitch<const char *>(Value)
+  return llvm::StringSwitch<const char *>(Value.lower())
     .Cases("arm9e", "arm946e-s", "arm966e-s", "arm968e-s", "arm926ej-s","armv5")
     .Cases("arm10e", "arm10tdmi", "armv5")
     .Cases("arm1020t", "arm1020e", "arm1022e", "arm1026ej-s", "armv5")
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -895,7 +895,7 @@
   if ((A = Args.getLastArg(options::OPT_mtune_EQ))) {
     CPU = A->getValue();
   } else if ((A = Args.getLastArg(options::OPT_mcpu_EQ))) {
-    StringRef Mcpu = A->getValue();
+    StringRef Mcpu = StringRef(A->getValue()).lower();
     CPU = Mcpu.split("+").first;
   }
 
@@ -1826,7 +1826,7 @@
                                const ArgList &Args,
                                std::vector<const char *> &Features) {
   StringRef CPU;
-  if (!DecodeAArch64Mcpu(D, Mcpu, CPU, Features))
+  if (!DecodeAArch64Mcpu(D, Mcpu.lower(), CPU, Features))
     return false;
 
   return true;
@@ -1852,7 +1852,7 @@
                                     std::vector<const char *> &Features) {
   StringRef CPU;
   std::vector<const char *> DecodedFeature;
-  if (!DecodeAArch64Mcpu(D, Mcpu, CPU, DecodedFeature))
+  if (!DecodeAArch64Mcpu(D, Mcpu.lower(), CPU, DecodedFeature))
     return false;
 
   return getAArch64MicroArchFeaturesFromMtune(D, CPU, Args, Features);
@@ -5613,7 +5613,7 @@
   // 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();
+    StringRef MCPU = StringRef(A->getValue()).lower();
     // Handle -mcpu=native.
     if (MCPU == "native")
       return llvm::sys::getHostCPUName();
@@ -7482,7 +7482,7 @@
     // 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);