[Driver] Reject -march= for ppc

[MaskRay]

Summary

Clang -march= for ppc triples currently leads to an
-Wunused-command-line-argument warning but GCC rejects -march=.

error: unrecognized command-line option ‘-march=xxx’

Let's reject -march= as well similar to the Sparc change D130273.

Close https://github.com/llvm/llvm-project/issues/57587

[nemanjai]

I am perfectly fine with this. That option is quite problematic. LGTM.

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

 
 enum class ReadGOTPtrMode {
   Bss,
   SecurePlt,
 };
 
 FloatABI getPPCFloatABI(const Driver &D, const llvm::opt::ArgList &Args);
 
-std::string getPPCTargetCPU(const llvm::opt::ArgList &Args,
+std::string getPPCTargetCPU(const Driver &D, const llvm::opt::ArgList &Args,
                             const llvm::Triple &T);
 const char *getPPCAsmModeForCPU(StringRef Name);
 ReadGOTPtrMode getPPCReadGOTPtrMode(const Driver &D, const llvm::Triple &Triple,
                                     const llvm::opt::ArgList &Args);
 
 void getPPCTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                           const llvm::opt::ArgList &Args,
                           std::vector<llvm::StringRef> &Features);
 
 } // end namespace ppc
 } // end namespace target
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_ARCH_PPC_H

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

else if (T.getArch() == llvm::Triple::ppc64le)
     return "ppc64le";
   else if (T.getArch() == llvm::Triple::ppc64)
     return "ppc64";
   else
     return "ppc";
 }
 
 /// getPPCTargetCPU - Get the (LLVM) name of the PowerPC cpu we are targeting.
-std::string ppc::getPPCTargetCPU(const ArgList &Args, const llvm::Triple &T) {
+std::string ppc::getPPCTargetCPU(const Driver &D, const ArgList &Args,
+                                 const llvm::Triple &T) {
+  if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_march_EQ)) {
+    D.Diag(diag::err_drv_unsupported_opt_for_target)
+        << A->getSpelling() << T.getTriple();
+  }
+
   if (Arg *A = Args.getLastArg(clang::driver::options::OPT_mcpu_EQ)) {
     StringRef CPUName = A->getValue();
 
     // Clang/LLVM does not actually support code generation
     // for the 405 CPU. However, there are uses of this CPU ID
     // in projects that previously used GCC and rely on Clang
     // accepting it. Clang has always ignored it and passed the
     // generic CPU ID to the back end.

clang/lib/Driver/ToolChains/CommonArgs.cpp

case llvm::Triple::nvptx64:
     if (const Arg *A = Args.getLastArg(options::OPT_march_EQ))
       return A->getValue();
     return "";
 
   case llvm::Triple::ppc:
   case llvm::Triple::ppcle:
   case llvm::Triple::ppc64:
   case llvm::Triple::ppc64le:
-    return ppc::getPPCTargetCPU(Args, T);
+    return ppc::getPPCTargetCPU(D, Args, T);
 
   case llvm::Triple::csky:
     if (const Arg *A = Args.getLastArg(options::OPT_mcpu_EQ))
       return A->getValue();
     else if (const Arg *A = Args.getLastArg(options::OPT_march_EQ))
       return A->getValue();
     else
       return "ck810";

clang/test/Driver/ppc-cpus.c

 // RUN: %clang -### -c --target=powerpc64 %s -mcpu=generic -mtune=pwr9 2>&1 | FileCheck %s --check-prefix=TUNE
 // TUNE: "-target-cpu" "ppc64" "-tune-cpu" "pwr9"
 
 /// Test mcpu options that are equivalent to "generic"
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=generic 2>&1 | FileCheck %s --check-prefix=GENERIC
 // RUN: %clang -### -c -target powerpc64 %s -mcpu=405     2>&1 | FileCheck %s --check-prefix=GENERIC
 //
 // GENERIC: "-target-cpu" "ppc64"
+
+// RUN: %clang -### -c --target=powerpc64 %s -march=generic 2>&1 | FileCheck --check-prefix=MARCH %s
+// MARCH: error: unsupported option '-march=' for target 'powerpc64'