Index: clang/lib/Driver/ToolChains/Arch/PPC.h
===================================================================
--- clang/lib/Driver/ToolChains/Arch/PPC.h
+++ clang/lib/Driver/ToolChains/Arch/PPC.h
@@ -35,7 +35,8 @@
 
 FloatABI getPPCFloatABI(const Driver &D, const llvm::opt::ArgList &Args);
 
-std::string getPPCTargetCPU(const llvm::opt::ArgList &Args);
+std::string getPPCTargetCPU(const llvm::opt::ArgList &Args,
+                            const llvm::Triple &T);
 const char *getPPCAsmModeForCPU(StringRef Name);
 ReadGOTPtrMode getPPCReadGOTPtrMode(const Driver &D, const llvm::Triple &Triple,
                                     const llvm::opt::ArgList &Args);
Index: clang/lib/Driver/ToolChains/Arch/PPC.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Arch/PPC.cpp
+++ clang/lib/Driver/ToolChains/Arch/PPC.cpp
@@ -20,74 +20,64 @@
 using namespace clang;
 using namespace llvm::opt;
 
+static std::string getPPCGenericTargetCPU(const llvm::Triple &T) {
+  // LLVM may default to generating code for the native CPU,
+  // but, like gcc, we default to a more generic option for
+  // each architecture. (except on AIX)
+  if (T.isOSAIX())
+    return "pwr7";
+  else if (T.getArch() == llvm::Triple::ppc64le)
+    return "ppc64le";
+  else if (T.getArch() == llvm::Triple::ppc64)
+    return "ppc64";
+  else
+    return "ppc";
+}
+
 /// getPPCTargetCPU - Get the (LLVM) name of the PowerPC cpu we are targeting.
-std::string ppc::getPPCTargetCPU(const ArgList &Args) {
+std::string ppc::getPPCTargetCPU(const ArgList &Args, const llvm::Triple &T) {
   if (Arg *A = Args.getLastArg(clang::driver::options::OPT_mcpu_EQ)) {
     StringRef CPUName = A->getValue();
 
+    if (CPUName == "generic")
+      return getPPCGenericTargetCPU(T);
+
     if (CPUName == "native") {
       std::string CPU = std::string(llvm::sys::getHostCPUName());
       if (!CPU.empty() && CPU != "generic")
         return CPU;
       else
-        return "";
+        return getPPCGenericTargetCPU(T);
     }
 
-    return llvm::StringSwitch<const char *>(CPUName)
-        .Case("common", "generic")
-        .Case("440", "440")
-        .Case("440fp", "440")
-        .Case("450", "450")
-        .Case("601", "601")
-        .Case("602", "602")
-        .Case("603", "603")
-        .Case("603e", "603e")
-        .Case("603ev", "603ev")
-        .Case("604", "604")
-        .Case("604e", "604e")
-        .Case("620", "620")
-        .Case("630", "pwr3")
-        .Case("G3", "g3")
-        .Case("7400", "7400")
-        .Case("G4", "g4")
-        .Case("7450", "7450")
-        .Case("G4+", "g4+")
-        .Case("750", "750")
-        .Case("8548", "e500")
-        .Case("970", "970")
-        .Case("G5", "g5")
-        .Case("a2", "a2")
-        .Case("e500", "e500")
-        .Case("e500mc", "e500mc")
-        .Case("e5500", "e5500")
-        .Case("power3", "pwr3")
-        .Case("power4", "pwr4")
-        .Case("power5", "pwr5")
-        .Case("power5x", "pwr5x")
-        .Case("power6", "pwr6")
-        .Case("power6x", "pwr6x")
-        .Case("power7", "pwr7")
-        .Case("power8", "pwr8")
-        .Case("power9", "pwr9")
-        .Case("power10", "pwr10")
-        .Case("future", "future")
-        .Case("pwr3", "pwr3")
-        .Case("pwr4", "pwr4")
-        .Case("pwr5", "pwr5")
-        .Case("pwr5x", "pwr5x")
-        .Case("pwr6", "pwr6")
-        .Case("pwr6x", "pwr6x")
-        .Case("pwr7", "pwr7")
-        .Case("pwr8", "pwr8")
-        .Case("pwr9", "pwr9")
-        .Case("pwr10", "pwr10")
-        .Case("powerpc", "ppc")
-        .Case("powerpc64", "ppc64")
-        .Case("powerpc64le", "ppc64le")
-        .Default("");
+    auto TargetCPUName = llvm::StringSwitch<llvm::StringRef>(CPUName)
+                             .Case("common", "generic")
+                             .Case("440fp", "440")
+                             .Case("630", "pwr3")
+                             .Case("G3", "g3")
+                             .Case("G4", "g4")
+                             .Case("G4+", "g4+")
+                             .Case("8548", "e500")
+                             .Case("G5", "g5")
+                             .Case("power3", "pwr3")
+                             .Case("power4", "pwr4")
+                             .Case("power5", "pwr5")
+                             .Case("power5x", "pwr5x")
+                             .Case("power6", "pwr6")
+                             .Case("power6x", "pwr6x")
+                             .Case("power7", "pwr7")
+                             .Case("power8", "pwr8")
+                             .Case("power9", "pwr9")
+                             .Case("power10", "pwr10")
+                             .Case("future", "future")
+                             .Case("powerpc", "ppc")
+                             .Case("powerpc64", "ppc64")
+                             .Case("powerpc64le", "ppc64le")
+                             .Default(CPUName);
+    return TargetCPUName.str();
   }
 
-  return "";
+  return getPPCGenericTargetCPU(T);
 }
 
 const char *ppc::getPPCAsmModeForCPU(StringRef Name) {
Index: clang/lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -409,25 +409,9 @@
   case llvm::Triple::ppc:
   case llvm::Triple::ppcle:
   case llvm::Triple::ppc64:
-  case llvm::Triple::ppc64le: {
-    std::string TargetCPUName = ppc::getPPCTargetCPU(Args);
-    // LLVM may default to generating code for the native CPU,
-    // but, like gcc, we default to a more generic option for
-    // each architecture. (except on AIX)
-    if (!TargetCPUName.empty())
-      return TargetCPUName;
-
-    if (T.isOSAIX())
-      TargetCPUName = "pwr7";
-    else if (T.getArch() == llvm::Triple::ppc64le)
-      TargetCPUName = "ppc64le";
-    else if (T.getArch() == llvm::Triple::ppc64)
-      TargetCPUName = "ppc64";
-    else
-      TargetCPUName = "ppc";
+  case llvm::Triple::ppc64le:
+    return ppc::getPPCTargetCPU(Args, T);
 
-    return TargetCPUName;
-  }
   case llvm::Triple::csky:
     if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ))
       return A->getValue();
Index: clang/test/Driver/ppc-cpus.c
===================================================================
--- clang/test/Driver/ppc-cpus.c
+++ clang/test/Driver/ppc-cpus.c
@@ -5,6 +5,15 @@
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=native 2>&1 | FileCheck --check-prefix=MCPU_NATIVE %s
 // MCPU_NATIVE-NOT: "-target-cpu" "native"
 
+/// Check that we are passing unknown mcpu options to the backend so an error
+/// can be triggered.
+// RUN: %clang -### -c -target powerpc64 %s -mcpu=asdf1234 2>&1 | FileCheck --check-prefix=MCPU_UNKNOWN %s
+// MCPU_UNKNOWN: "-target-cpu" "asdf1234"
+
+/// Check for the unknown target error if an unknown mcpu option is used.
+// RUN: not %clang -c -target powerpc64 %s -mcpu=asdf1234 2>&1 | FileCheck --check-prefix=MCPU_ERR %s
+// MCPU_ERR: unknown target CPU 'asdf1234'
+
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=7400 2>&1 | FileCheck --check-prefix=MCPU_7400 %s
 // MCPU_7400: "-target-cpu" "7400"