Index: clang/include/clang/AST/Attr.h
===================================================================
--- clang/include/clang/AST/Attr.h
+++ clang/include/clang/AST/Attr.h
@@ -334,11 +334,17 @@
 struct ParsedTargetAttr {
   std::vector<std::string> Features;
   StringRef Architecture;
+  StringRef Tune;
   StringRef BranchProtection;
   bool DuplicateArchitecture = false;
+  bool DuplicateTune = false;
   bool operator ==(const ParsedTargetAttr &Other) const {
     return DuplicateArchitecture == Other.DuplicateArchitecture &&
-           Architecture == Other.Architecture && Features == Other.Features;
+           DuplicateTune == Other.DuplicateTune &&
+           Architecture == Other.Architecture &&
+           Tune == Other.Tune &&
+           BranchProtection == Other.BranchProtection &&
+           Features == Other.Features;
   }
 };
 
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2346,11 +2346,10 @@
         // accepting it weirdly.
         Feature = Feature.trim();
 
-        // We don't support cpu tuning this way currently.
         // TODO: Support the fpmath option. It will require checking
         // overall feature validity for the function with the rest of the
         // attributes on the function.
-        if (Feature.startswith("fpmath=") || Feature.startswith("tune="))
+        if (Feature.startswith("fpmath="))
           continue;
 
         if (Feature.startswith("branch-protection=")) {
@@ -2364,6 +2363,11 @@
             Ret.DuplicateArchitecture = true;
           else
             Ret.Architecture = Feature.split("=").second.trim();
+        } else if (Feature.startswith("tune=")) {
+          if (!Ret.Tune.empty())
+            Ret.DuplicateTune = true;
+          else
+            Ret.Tune = Feature.split("=").second.trim();
         } else if (Feature.startswith("no-"))
           Ret.Features.push_back("-" + Feature.split("-").second.str());
         else
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -1898,6 +1898,9 @@
 of the feature, as well as ``arch="CPU"`` which will change the default "CPU"
 for the function.
 
+For X86, the attribute also allows ``tune="CPU"`` to optimize the generated
+code for the given CPU without changing the available instructions.
+
 For AArch64, the attribute also allows the "branch-protection=<args>" option,
 where the permissible arguments and their effect on code generation are the same
 as for the command-line option ``-mbranch-protection``.
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2829,8 +2829,9 @@
 def err_invalid_branch_protection_spec : Error<
   "invalid or misplaced branch protection specification '%0'">;
 def warn_unsupported_target_attribute
-    : Warning<"%select{unsupported|duplicate}0%select{| architecture}1 '%2' in"
-              " the 'target' attribute string; 'target' attribute ignored">,
+    : Warning<"%select{unsupported|duplicate}0%select{| architecture| tune}1 "
+              "'%2' in the 'target' attribute string; 'target' attribute "
+              "ignored">,
       InGroup<IgnoredAttributes>;
 def err_attribute_unsupported
     : Error<"%0 attribute is not supported for this target">;
Index: clang/include/clang/Basic/TargetInfo.h
===================================================================
--- clang/include/clang/Basic/TargetInfo.h
+++ clang/include/clang/Basic/TargetInfo.h
@@ -1148,6 +1148,11 @@
     return true;
   }
 
+  /// brief Determine whether this TargetInfo supports tune in target attribute.
+  virtual bool supportsTargetAttributeTune() const {
+    return false;
+  }
+
   /// Use the specified ABI.
   ///
   /// \return False on error (invalid ABI name).
Index: clang/lib/Basic/Targets/X86.h
===================================================================
--- clang/lib/Basic/Targets/X86.h
+++ clang/lib/Basic/Targets/X86.h
@@ -296,6 +296,10 @@
     return "";
   }
 
+  bool supportsTargetAttributeTune() const override {
+    return true;
+  }
+
   bool isValidCPUName(StringRef Name) const override {
     bool Only64Bit = getTriple().getArch() != llvm::Triple::x86;
     return llvm::X86::parseArchX86(Name, Only64Bit) != llvm::X86::CK_None;
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -1770,9 +1770,14 @@
     // the function.
     if (TD) {
       ParsedTargetAttr ParsedAttr = TD->parse();
-      if (ParsedAttr.Architecture != "" &&
-          getTarget().isValidCPUName(ParsedAttr.Architecture))
+      if (!ParsedAttr.Architecture.empty() &&
+          getTarget().isValidCPUName(ParsedAttr.Architecture)) {
         TargetCPU = ParsedAttr.Architecture;
+        TuneCPU = ""; // Clear the tune CPU.
+      }
+      if (!ParsedAttr.Tune.empty() &&
+          getTarget().isValidCPUName(ParsedAttr.Tune))
+        TuneCPU = ParsedAttr.Tune;
     }
   } else {
     // Otherwise just add the existing target cpu and target features to the
@@ -1780,11 +1785,11 @@
     Features = getTarget().getTargetOpts().Features;
   }
 
-  if (TargetCPU != "") {
+  if (!TargetCPU.empty()) {
     Attrs.addAttribute("target-cpu", TargetCPU);
     AddedAttr = true;
   }
-  if (TuneCPU != "") {
+  if (!TuneCPU.empty()) {
     Attrs.addAttribute("tune-cpu", TuneCPU);
     AddedAttr = true;
   }
@@ -1826,6 +1831,7 @@
         // new ones should replace the old.
         F->removeFnAttr("target-cpu");
         F->removeFnAttr("target-features");
+        F->removeFnAttr("tune-cpu");
         F->addAttributes(llvm::AttributeList::FunctionIndex, Attrs);
       }
     }
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -3063,11 +3063,16 @@
 // 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)
-      return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
-             << Unsupported << None << Str;
+  enum SecondParam { None, Architecture, Tune };
+  if (AttrStr.find("fpmath=") != StringRef::npos)
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Unsupported << None << "fpmath=";
+
+  // Diagnose use of tune if target doesn't support it.
+  if (!Context.getTargetInfo().supportsTargetAttributeTune() &&
+      AttrStr.find("tune=") != StringRef::npos)
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Unsupported << None << "tune=";
 
   ParsedTargetAttr ParsedAttrs = TargetAttr::parse(AttrStr);
 
@@ -3076,9 +3081,17 @@
     return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
            << Unsupported << Architecture << ParsedAttrs.Architecture;
 
+  if (!ParsedAttrs.Tune.empty() &&
+      !Context.getTargetInfo().isValidCPUName(ParsedAttrs.Tune))
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Unsupported << Tune << ParsedAttrs.Tune;
+
   if (ParsedAttrs.DuplicateArchitecture)
     return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
            << Duplicate << None << "arch=";
+  if (ParsedAttrs.DuplicateTune)
+    return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
+           << Duplicate << None << "tune=";
 
   for (const auto &Feature : ParsedAttrs.Features) {
     auto CurFeature = StringRef(Feature).drop_front(); // remove + or -.
Index: clang/test/CodeGen/attr-target-x86.c
===================================================================
--- clang/test/CodeGen/attr-target-x86.c
+++ clang/test/CodeGen/attr-target-x86.c
@@ -1,10 +1,9 @@
-// RUN: %clang_cc1 -triple i686-linux-gnu -target-cpu i686 -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i686-linux-gnu -target-cpu i686 -tune-cpu i686 -emit-llvm %s -o - | FileCheck %s
 
 int baz(int a) { return 4; }
 
 int __attribute__((target("avx,sse4.2,arch=ivybridge"))) foo(int a) { return 4; }
 
-int __attribute__((target("tune=sandybridge"))) walrus(int a) { return 4; }
 int __attribute__((target("fpmath=387"))) koala(int a) { return 4; }
 
 int __attribute__((target("no-sse2"))) echidna(int a) { return 4; }
@@ -31,12 +30,11 @@
   return 5;
 }
 
+int __attribute__((target("tune=sandybridge"))) walrus(int a) { return 4; }
 
 // Check that we emit the additional subtarget and cpu features for foo and not for baz or bar.
 // CHECK: baz{{.*}} #0
 // CHECK: foo{{.*}} #1
-// We ignore the tune attribute so walrus should be identical to baz and bar.
-// CHECK: walrus{{.*}} #0
 // We're currently ignoring the fpmath attribute so koala should be identical to baz and bar.
 // CHECK: koala{{.*}} #0
 // CHECK: echidna{{.*}} #2
@@ -48,11 +46,16 @@
 // CHECK: qq{{.*}} #6
 // CHECK: lake{{.*}} #7
 // CHECK: use_before_def{{.*}} #7
-// CHECK: #0 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87"
+// CHECK: walrus{{.*}} #8
+// CHECK: #0 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87" "tune-cpu"="i686"
 // CHECK: #1 = {{.*}}"target-cpu"="ivybridge" "target-features"="+avx,+cx16,+cx8,+f16c,+fsgsbase,+fxsr,+mmx,+pclmul,+popcnt,+rdrnd,+sahf,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave,+xsaveopt"
-// CHECK: #2 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87,-aes,-avx,-avx2,-avx512bf16,-avx512bitalg,-avx512bw,-avx512cd,-avx512dq,-avx512er,-avx512f,-avx512ifma,-avx512pf,-avx512vbmi,-avx512vbmi2,-avx512vl,-avx512vnni,-avx512vp2intersect,-avx512vpopcntdq,-f16c,-fma,-fma4,-gfni,-pclmul,-sha,-sse2,-sse3,-sse4.1,-sse4.2,-sse4a,-ssse3,-vaes,-vpclmulqdq,-xop"
-// CHECK: #3 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+mmx,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87"
-// CHECK: #4 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87,-avx,-avx2,-avx512bf16,-avx512bitalg,-avx512bw,-avx512cd,-avx512dq,-avx512er,-avx512f,-avx512ifma,-avx512pf,-avx512vbmi,-avx512vbmi2,-avx512vl,-avx512vnni,-avx512vp2intersect,-avx512vpopcntdq,-f16c,-fma,-fma4,-sse4.1,-sse4.2,-vaes,-vpclmulqdq,-xop"
+// CHECK-NOT: tune-cpu
+// CHECK: #2 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87,-aes,-avx,-avx2,-avx512bf16,-avx512bitalg,-avx512bw,-avx512cd,-avx512dq,-avx512er,-avx512f,-avx512ifma,-avx512pf,-avx512vbmi,-avx512vbmi2,-avx512vl,-avx512vnni,-avx512vp2intersect,-avx512vpopcntdq,-f16c,-fma,-fma4,-gfni,-pclmul,-sha,-sse2,-sse3,-sse4.1,-sse4.2,-sse4a,-ssse3,-vaes,-vpclmulqdq,-xop" "tune-cpu"="i686"
+// CHECK: #3 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+mmx,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87" "tune-cpu"="i686"
+// CHECK: #4 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87,-avx,-avx2,-avx512bf16,-avx512bitalg,-avx512bw,-avx512cd,-avx512dq,-avx512er,-avx512f,-avx512ifma,-avx512pf,-avx512vbmi,-avx512vbmi2,-avx512vl,-avx512vnni,-avx512vp2intersect,-avx512vpopcntdq,-f16c,-fma,-fma4,-sse4.1,-sse4.2,-vaes,-vpclmulqdq,-xop" "tune-cpu"="i686"
 // CHECK: #5 = {{.*}}"target-cpu"="ivybridge" "target-features"="+avx,+cx16,+cx8,+f16c,+fsgsbase,+fxsr,+mmx,+pclmul,+popcnt,+rdrnd,+sahf,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave,+xsaveopt,-aes,-vaes"
+// CHECK-NOT: tune-cpu
 // CHECK: #6 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87,-3dnow,-3dnowa,-mmx"
 // CHECK: #7 = {{.*}}"target-cpu"="lakemont" "target-features"="+cx8,+mmx"
+// CHECK-NOT: tune-cpu
+// CHECK: #8 = {{.*}}"target-cpu"="i686" "target-features"="+cx8,+x87" "tune-cpu"="sandybridge"
Index: clang/test/Sema/attr-target.c
===================================================================
--- clang/test/Sema/attr-target.c
+++ clang/test/Sema/attr-target.c
@@ -1,9 +1,12 @@
 // RUN: %clang_cc1 -triple x86_64-linux-gnu  -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnu  -fsyntax-only -verify %s
+
+#ifdef __x86_64__
 
 int __attribute__((target("avx,sse4.2,arch=ivybridge"))) foo() { return 4; }
 //expected-error@+1 {{'target' attribute takes one argument}}
 int __attribute__((target())) bar() { return 4; }
-//expected-warning@+1 {{unsupported 'tune=' in the 'target' attribute string; 'target' attribute ignored}}
+// no warning, tune is supported for x86
 int __attribute__((target("tune=sandybridge"))) baz() { return 4; }
 //expected-warning@+1 {{unsupported 'fpmath=' in the 'target' attribute string; 'target' attribute ignored}}
 int __attribute__((target("fpmath=387"))) walrus() { return 4; }
@@ -19,4 +22,13 @@
 int __attribute__((target("arch=ivybridge,arch=haswell"))) oak_tree() { return 4; }
 //expected-warning@+1 {{unsupported 'branch-protection' in the 'target' attribute string; 'target' attribute ignored}}
 int __attribute__((target("branch-protection=none"))) birch_tree() { return 5; }
+//expected-warning@+1 {{unsupported tune 'hiss' in the 'target' attribute string; 'target' attribute ignored}}
+int __attribute__((target("tune=hiss,tune=woof"))) apple_tree() { return 4; }
+
+#else
+
+// tune is not supported by other targets.
+//expected-warning@+1 {{unsupported 'tune=' in the 'target' attribute string; 'target' attribute ignored}}
+int __attribute__((target("tune=hiss"))) baz() { return 4; }
 
+#endif