[Driver][PowerPC] Support -mtune=

[nemanjai]

Thanks. We'll eventually start doing something with the option in the back end. LGTM.

clang/include/clang/Driver/Options.td

def mno_relax_pic_calls : Flag<["-"], "mno-relax-pic-calls">,
   HelpText<"Do not produce relaxation hints for linkers to try optimizing PIC "
            "call sequences into direct calls (MIPS only)">, Flags<[HelpHidden]>;
 def mglibc : Flag<["-"], "mglibc">, Group<m_libc_Group>, Flags<[HelpHidden]>;
 def muclibc : Flag<["-"], "muclibc">, Group<m_libc_Group>, Flags<[HelpHidden]>;
 def module_file_info : Flag<["-"], "module-file-info">, Flags<[NoXarchOption,CC1Option]>, Group<Action_Group>,
   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">;
 def mwarn_nonportable_cfstrings : Flag<["-"], "mwarn-nonportable-cfstrings">, Group<m_Group>;
 def canonical_prefixes : Flag<["-"], "canonical-prefixes">, Flags<[HelpHidden, CoreOption]>,
   HelpText<"Use absolute paths for invoking subcommands (default)">;
 def no_canonical_prefixes : Flag<["-"], "no-canonical-prefixes">, Flags<[HelpHidden, CoreOption]>,
   HelpText<"Use relative paths for invoking subcommands">;

clang/lib/Driver/ToolChains/Arch/PPC.cpp

return llvm::StringSwitch<const char *>(Name)
       .Case("pwr10", "-mpower10")
       .Case("power10", "-mpower10")
       .Default("-many");
 }
 
 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");
 
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_ppc_Features_Group);
 
   ppc::FloatABI FloatABI = ppc::getPPCFloatABI(D, Args);
   if (FloatABI == ppc::FloatABI::Soft)
     Features.push_back("-hard-float");

clang/lib/Driver/ToolChains/Clang.cpp

if (A->getOption().matches(options::OPT_mno_relax_pic_calls)) {
       CmdArgs.push_back("-mllvm");
       CmdArgs.push_back("-mips-jalr-reloc=0");
     }
   }
 }
 
 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();
   if (T.isOSBinFormatELF()) {
     switch (getToolChain().getArch()) {
     case llvm::Triple::ppc64: {
       if ((T.isOSFreeBSD() && T.getOSMajorVersion() >= 13) ||
           T.isOSOpenBSD() || T.isMusl())

clang/test/Driver/ppc-cpus.c

 // RUN: %clang -### -c -target powerpc64 %s -mcpu=G4+ 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=970 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=G5 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=pwr6 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=pwr7 2>&1 | FileCheck %s --check-prefix=NO_PPC64
 // 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"