Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2387,8 +2387,9 @@
 def err_attribute_requires_opencl_version : Error<
   "%0 attribute requires OpenCL version %1%select{| or above}2">;
 def warn_unsupported_target_attribute
-    : Warning<"Ignoring unsupported '%0' in the target attribute string">,
-    InGroup<IgnoredAttributes>;
+    : Warning<"ignoring %select{unsupported|duplicate}0"
+              "%select{| architecture}1 '%2' in the target attribute string">,
+      InGroup<IgnoredAttributes>;
 def err_attribute_unsupported
     : Error<"%0 attribute is not supported for this target">;
 // The err_*_attribute_argument_not_int are separate because they're used by
Index: include/clang/Sema/Sema.h
===================================================================
--- include/clang/Sema/Sema.h
+++ include/clang/Sema/Sema.h
@@ -3271,7 +3271,7 @@
                                       unsigned ArgNum, StringRef &Str,
                                       SourceLocation *ArgLocation = nullptr);
   bool checkSectionName(SourceLocation LiteralLoc, StringRef Str);
-  void checkTargetAttr(SourceLocation LiteralLoc, StringRef Str);
+  bool checkTargetAttr(SourceLocation LiteralLoc, StringRef Str);
   bool checkMSInheritanceAttrOnDefinition(
       CXXRecordDecl *RD, SourceRange Range, bool BestCase,
       MSInheritanceAttr::Spelling SemanticSpelling);
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -2993,22 +2993,43 @@
     D->addAttr(NewAttr);
 }
 
-// Check for things we'd like to warn about, no errors or validation for now.
-// TODO: Validation should use a backend target library that specifies
-// the allowable subtarget features and cpus. We could use something like a
-// TargetCodeGenInfo hook here to do validation.
-void Sema::checkTargetAttr(SourceLocation LiteralLoc, StringRef AttrStr) {
+// Check for things we'd like to warn about. Multiversioning issues are
+// handled later in the process, once we know how many exist.
+bool Sema::checkTargetAttr(SourceLocation LiteralLoc, StringRef AttrStr) {
+  enum FirstParam { Unsupported, Duplicate };
+  enum SecondParam { None, Architecture };
   for (auto Str : {"tune=", "fpmath="})
     if (AttrStr.find(Str) != StringRef::npos)
-      Diag(LiteralLoc, diag::warn_unsupported_target_attribute) << Str;
+      return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+             << Unsupported << None << Str;
+
+  TargetAttr::ParsedTargetAttr ParsedAttrs = TargetAttr::parse(AttrStr);
+
+  if (!ParsedAttrs.Architecture.empty() &&
+      !Context.getTargetInfo().isValidCPUName(ParsedAttrs.Architecture))
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Unsupported << Architecture << ParsedAttrs.Architecture;
+
+  if (ParsedAttrs.DuplicateArchitecture)
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Duplicate << None << "arch=";
+
+  for (const auto &Feature : ParsedAttrs.Features) {
+    auto CurFeature = StringRef(Feature).drop_front(); // remove + or -.
+    if (!Context.getTargetInfo().isValidFeatureName(CurFeature))
+      return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+             << Unsupported << None << CurFeature;
+  }
+
+  return true;
 }
 
 static void handleTargetAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   StringRef Str;
   SourceLocation LiteralLoc;
-  if (!S.checkStringLiteralArgumentAttr(Attr, 0, Str, &LiteralLoc))
+  if (!S.checkStringLiteralArgumentAttr(Attr, 0, Str, &LiteralLoc) ||
+      !S.checkTargetAttr(LiteralLoc, Str))
     return;
-  S.checkTargetAttr(LiteralLoc, Str);
   unsigned Index = Attr.getAttributeSpellingListIndex();
   TargetAttr *NewAttr =
       ::new (S.Context) TargetAttr(Attr.getRange(), S.Context, Str, Index);
Index: test/Sema/attr-target.c
===================================================================
--- test/Sema/attr-target.c
+++ test/Sema/attr-target.c
@@ -2,7 +2,13 @@
 
 int __attribute__((target("avx,sse4.2,arch=ivybridge"))) foo() { return 4; }
 int __attribute__((target())) bar() { return 4; } //expected-error {{'target' attribute takes one argument}}
-int __attribute__((target("tune=sandybridge"))) baz() { return 4; } //expected-warning {{Ignoring unsupported 'tune=' in the target attribute string}}
-int __attribute__((target("fpmath=387"))) walrus() { return 4; } //expected-warning {{Ignoring unsupported 'fpmath=' in the target attribute string}}
+int __attribute__((target("tune=sandybridge"))) baz() { return 4; } //expected-warning {{ignoring unsupported 'tune=' in the target attribute string}}
+int __attribute__((target("fpmath=387"))) walrus() { return 4; } //expected-warning {{ignoring unsupported 'fpmath=' in the target attribute string}}
+int __attribute__((target("avx,sse4.2,arch=hiss"))) meow() {  return 4; }//expected-warning {{ignoring unsupported architecture 'hiss' in the target attribute string}}
+int __attribute__((target("woof"))) bark() {  return 4; }//expected-warning {{ignoring unsupported 'woof' in the target attribute string}}
+int __attribute__((target("arch="))) turtle() { return 4; } // no warning, same as saying 'nothing'.
+int __attribute__((target("arch=hiss,arch=woof"))) pine_tree() { return 4; } //expected-warning {{ignoring unsupported architecture 'hiss' in the target attribute string}}
+int __attribute__((target("arch=ivybridge,arch=haswell"))) oak_tree() { return 4; } //expected-warning {{ignoring duplicate 'arch=' in the target attribute string}}
+