[SystemZ] Enable -mtune= option in clang.

https://reviews.llvm.org/D128910 enabled handling of
attribute "tune-cpu" in LLVM. This PR now enables
option `-mtune` in clang, which then generates the
new attribute.

Reviewed By: uweigand

Differential Revision: https://reviews.llvm.org/D129562

Author: redstar

clang/docs/ClangCommandLineReference.rst

@@ -3325,7 +3325,7 @@ Specify bit size of immediate TLS offsets (AArch64 ELF only): 12 (for 4KB) \| 24
 .. option:: -mtune=<arg>
 .. program:: clang
 
-Only supported on X86 and RISC-V. Otherwise accepted for compatibility with GCC.
+Only supported on X86, RISC-V and SystemZ. Otherwise accepted for compatibility with GCC.
 
 .. option:: -mtvos-version-min=<arg>, -mappletvos-version-min=<arg>
 

clang/include/clang/Driver/Options.td

@@ -3950,7 +3950,7 @@ def module_file_info : Flag<["-"], "module-file-info">, Flags<[NoXarchOption,CC1
   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 and RISC-V. Otherwise accepted for compatibility with GCC.">;
+  HelpText<"Only supported on X86, RISC-V and SystemZ. Otherwise accepted for compatibility with GCC.">;
 def multi__module : Flag<["-"], "multi_module">;
 def multiply__defined__unused : Separate<["-"], "multiply_defined_unused">;
 def multiply__defined : Separate<["-"], "multiply_defined">;

clang/lib/Basic/Targets/SystemZ.h

@@ -123,6 +123,14 @@ class LLVM_LIBRARY_VISIBILITY SystemZTargetInfo : public TargetInfo {
 
   void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const override;
 
+  bool isValidTuneCPUName(StringRef Name) const override {
+    return isValidCPUName(Name);
+  }
+
+  void fillValidTuneCPUList(SmallVectorImpl<StringRef> &Values) const override {
+    fillValidCPUList(Values);
+  }
+
   bool setCPU(const std::string &Name) override {
     CPU = Name;
     ISARevision = getISARevision(CPU);

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2228,8 +2228,23 @@ void Clang::AddSparcTargetArgs(const ArgList &Args,
 
 void Clang::AddSystemZTargetArgs(const ArgList &Args,
                                  ArgStringList &CmdArgs) const {
-  bool HasBackchain = Args.hasFlag(options::OPT_mbackchain,
-                                   options::OPT_mno_backchain, false);
+  if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_mtune_EQ)) {
+    StringRef Name = A->getValue();
+
+    std::string TuneCPU;
+    if (Name == "native")
+      TuneCPU = std::string(llvm::sys::getHostCPUName());
+    else
+      TuneCPU = std::string(Name);
+
+    if (!TuneCPU.empty()) {
+      CmdArgs.push_back("-tune-cpu");
+      CmdArgs.push_back(Args.MakeArgString(TuneCPU));
+    }
+  }
+
+  bool HasBackchain =
+      Args.hasFlag(options::OPT_mbackchain, options::OPT_mno_backchain, false);
   bool HasPackedStack = Args.hasFlag(options::OPT_mpacked_stack,
                                      options::OPT_mno_packed_stack, false);
   systemz::FloatABI FloatABI =