Index: include/clang/Basic/DiagnosticCommonKinds.td
===================================================================
--- include/clang/Basic/DiagnosticCommonKinds.td
+++ include/clang/Basic/DiagnosticCommonKinds.td
@@ -188,6 +188,7 @@
 def err_target_unknown_triple : Error<
   "unknown target triple '%0', please use -triple or -arch">;
 def err_target_unknown_cpu : Error<"unknown target CPU '%0'">;
+def note_valid_options : Note<"valid target CPU values are: %0">;
 def err_target_unsupported_cpu_for_micromips : Error<
   "micromips is not supported for target CPU '%0'">;
 def err_target_unknown_abi : Error<"unknown target ABI '%0'">;
Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -867,6 +867,9 @@
     return false;
   }
 
+  /// Fill a SmallVectorImpl with the valid values to setCPU.
+  virtual void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {}
+
   /// brief Determine whether this TargetInfo supports the given CPU name.
   virtual bool isValidCPUName(StringRef Name) const {
     return true;
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -38,6 +38,7 @@
 #include "Targets/X86.h"
 #include "Targets/XCore.h"
 #include "clang/Basic/Diagnostic.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
 
 using namespace clang;
@@ -607,6 +608,10 @@
   // Set the target CPU if specified.
   if (!Opts->CPU.empty() && !Target->setCPU(Opts->CPU)) {
     Diags.Report(diag::err_target_unknown_cpu) << Opts->CPU;
+    SmallVector<StringRef, 32> ValidList;
+    Target->fillValidCPUList(ValidList);
+    if (!ValidList.empty())
+      Diags.Report(diag::note_valid_options) << llvm::join(ValidList, ", ");
     return nullptr;
   }
 
Index: lib/Basic/Targets/AArch64.h
===================================================================
--- lib/Basic/Targets/AArch64.h
+++ lib/Basic/Targets/AArch64.h
@@ -46,6 +46,7 @@
   bool setABI(const std::string &Name) override;
 
   bool isValidCPUName(StringRef Name) const override;
+  void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const override;
   bool setCPU(const std::string &Name) override;
 
   bool useFP16ConversionIntrinsics() const override {
Index: lib/Basic/Targets/AArch64.cpp
===================================================================
--- lib/Basic/Targets/AArch64.cpp
+++ lib/Basic/Targets/AArch64.cpp
@@ -101,6 +101,11 @@
   return isValidCPUName(Name);
 }
 
+void AArch64TargetInfo::fillValidCPUList(
+    SmallVectorImpl<StringRef> &Values) const {
+  llvm::AArch64::fillValidCPUArchList(Values);
+}
+
 void AArch64TargetInfo::getTargetDefinesARMV81A(const LangOptions &Opts,
                                                 MacroBuilder &Builder) const {
   Builder.defineMacro("__ARM_FEATURE_QRDMX", "1");
Index: lib/Basic/Targets/ARM.h
===================================================================
--- lib/Basic/Targets/ARM.h
+++ lib/Basic/Targets/ARM.h
@@ -122,6 +122,8 @@
   bool hasFeature(StringRef Feature) const override;
 
   bool isValidCPUName(StringRef Name) const override;
+  void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const override;
+
   bool setCPU(const std::string &Name) override;
 
   bool setFPMath(StringRef Name) override;
Index: lib/Basic/Targets/ARM.cpp
===================================================================
--- lib/Basic/Targets/ARM.cpp
+++ lib/Basic/Targets/ARM.cpp
@@ -478,6 +478,10 @@
          llvm::ARM::parseCPUArch(Name) != llvm::ARM::ArchKind::INVALID;
 }
 
+void ARMTargetInfo::fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {
+  llvm::ARM::fillValidCPUArchList(Values);
+}
+
 bool ARMTargetInfo::setCPU(const std::string &Name) {
   if (Name != "generic")
     setArchInfo(llvm::ARM::parseCPUArch(Name));
Index: test/Misc/target-invalid-cpu-note.c
===================================================================
--- /dev/null
+++ test/Misc/target-invalid-cpu-note.c
@@ -0,0 +1,8 @@
+// RUN: not %clang_cc1 -triple armv5--- -target-cpu not-a-cpu -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix ARM
+// ARM: error: unknown target CPU 'not-a-cpu'
+// ARM: note: valid target CPU values are: arm2, arm3, arm6, arm7m, arm8, arm810, strongarm, strongarm110, strongarm1100, strongarm1110, arm7tdmi, arm7tdmi-s, arm710t, arm720t, arm9, arm9tdmi, arm920, arm920t, arm922t, arm9312, arm940t, ep9312, arm10tdmi, arm1020t, arm9e, arm946e-s, arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s, arm1136j-s, arm1136jf-s, arm1136jz-s, arm1176j-s, arm1176jz-s, mpcore, mpcorenovfp, arm1176jzf-s, arm1156t2-s, arm1156t2f-s, cortex-m0, cortex-m0plus, cortex-m1, sc000, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17, krait, cortex-r4, cortex-r4f, cortex-r5, cortex-r7, cortex-r8, cortex-r52, sc300, cortex-m3, cortex-m4, cortex-m7, cortex-m23, cortex-m33, cortex-a32, cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, cyclone, exynos-m1, exynos-m2, exynos-m3, kryo, iwmmxt, xscale, swift
+
+// RUN: not %clang_cc1 -triple arm64--- -target-cpu not-a-cpu -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix AARCH64
+// AARCH64: error: unknown target CPU 'not-a-cpu'
+// AARCH64: note: valid target CPU values are: cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, cyclone, exynos-m1, exynos-m2, exynos-m3, falkor, saphira, kryo, thunderx2t99, thunderx, thunderxt88, thunderxt81, thunderxt83
+