diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3986,7 +3986,7 @@
   HelpText<"Provide information about a particular module file">;
 def mthumb : Flag<["-"], "mthumb">, Group<m_Group>;
 def mtune_EQ : Joined<["-"], "mtune=">, Group<m_Group>,
-  HelpText<"Only supported on X86, RISC-V and SystemZ. Otherwise accepted for compatibility with GCC.">;
+  HelpText<"Only supported on AArch64, PowerPC, RISC-V, SystemZ, and X86">;
 def multi__module : Flag<["-"], "multi_module">;
 def multiply__defined__unused : Separate<["-"], "multiply_defined_unused">;
 def multiply__defined : Separate<["-"], "multiply_defined">;
diff --git a/clang/lib/Driver/ToolChains/Arch/PPC.cpp b/clang/lib/Driver/ToolChains/Arch/PPC.cpp
--- a/clang/lib/Driver/ToolChains/Arch/PPC.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/PPC.cpp
@@ -107,10 +107,6 @@
 void ppc::getPPCTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                const ArgList &Args,
                                std::vector<StringRef> &Features) {
-  // TODO Handle -mtune=. Suppress -Wunused-command-line-argument as a
-  // longstanding behavior.
-  (void)Args.getLastArg(options::OPT_mtune_EQ);
-
   if (Triple.getSubArch() == llvm::Triple::PPCSubArch_spe)
     Features.push_back("+spe");
 
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2083,6 +2083,14 @@
 
 void Clang::AddPPCTargetArgs(const ArgList &Args,
                              ArgStringList &CmdArgs) const {
+  if (const Arg *A = Args.getLastArg(options::OPT_mtune_EQ)) {
+    CmdArgs.push_back("-tune-cpu");
+    if (strcmp(A->getValue(), "native") == 0)
+      CmdArgs.push_back(Args.MakeArgString(llvm::sys::getHostCPUName()));
+    else
+      CmdArgs.push_back(A->getValue());
+  }
+
   // Select the ABI to use.
   const char *ABIName = nullptr;
   const llvm::Triple &T = getToolChain().getTriple();
diff --git a/clang/test/Driver/ppc-cpus.c b/clang/test/Driver/ppc-cpus.c
--- a/clang/test/Driver/ppc-cpus.c
+++ b/clang/test/Driver/ppc-cpus.c
@@ -19,3 +19,6 @@
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=pwr8 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 
 // NO_PPC64-NOT: "-target-cpu" "ppc64"
+
+// RUN: %clang -### -c --target=powerpc64 %s -mcpu=generic -mtune=pwr9 2>&1 | FileCheck %s --check-prefix=TUNE
+// TUNE: "-target-cpu" "ppc64" "-tune-cpu" "pwr9"