[Clang] Fix Hurd toolchain test on a two-stage build with ThinLTO

A two-stage ThinLTO build previously failed the clang/test/Driver/hurd.c test because of a static_cast in "tools::gnutools::Linker::ConstructJob()" which wrongly converted an instance of "clang::driver::toolchains::Hurd" into that of "clang::driver::toolchains::Linux". ThinLTO would later devirtualize the "ToolChain.getDynamicLinker(Args)" call and use "Linux::getDynamicLinker()" instead, causing the test to generate a wrong "-dynamic-linker" linker flag (/lib/ld-linux.so.2 instead of /lib/ld.so)

Fixes PR45061.

Differential Revision: https://reviews.llvm.org/D75373

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -309,25 +309,24 @@ static const char *getLDMOption(const llvm::Triple &T, const ArgList &Args) {
   }
 }
 
-static bool getPIE(const ArgList &Args, const toolchains::Linux &ToolChain) {
+static bool getPIE(const ArgList &Args, const ToolChain &TC) {
   if (Args.hasArg(options::OPT_shared) || Args.hasArg(options::OPT_static) ||
       Args.hasArg(options::OPT_r) || Args.hasArg(options::OPT_static_pie))
     return false;
 
   Arg *A = Args.getLastArg(options::OPT_pie, options::OPT_no_pie,
                            options::OPT_nopie);
   if (!A)
-    return ToolChain.isPIEDefault();
+    return TC.isPIEDefault();
   return A->getOption().matches(options::OPT_pie);
 }
 
-static bool getStaticPIE(const ArgList &Args,
-                         const toolchains::Linux &ToolChain) {
+static bool getStaticPIE(const ArgList &Args, const ToolChain &TC) {
   bool HasStaticPIE = Args.hasArg(options::OPT_static_pie);
   // -no-pie is an alias for -nopie. So, handling -nopie takes care of
   // -no-pie as well.
   if (HasStaticPIE && Args.hasArg(options::OPT_nopie)) {
-    const Driver &D = ToolChain.getDriver();
+    const Driver &D = TC.getDriver();
     const llvm::opt::OptTable &Opts = D.getOpts();
     const char *StaticPIEName = Opts.getOptionName(options::OPT_static_pie);
     const char *NoPIEName = Opts.getOptionName(options::OPT_nopie);
@@ -346,8 +345,12 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                            const InputInfoList &Inputs,
                                            const ArgList &Args,
                                            const char *LinkingOutput) const {
-  const toolchains::Linux &ToolChain =
-      static_cast<const toolchains::Linux &>(getToolChain());
+  // FIXME: The Linker class constructor takes a ToolChain and not a
+  // Generic_ELF, so the static_cast might return a reference to a invalid
+  // instance (see PR45061). Ideally, the Linker constructor needs to take a
+  // Generic_ELF instead.
+  const toolchains::Generic_ELF &ToolChain =
+      static_cast<const toolchains::Generic_ELF &>(getToolChain());
   const Driver &D = ToolChain.getDriver();
 
   const llvm::Triple &Triple = getToolChain().getEffectiveTriple();
@@ -418,8 +421,7 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (isAndroid)
       CmdArgs.push_back("--warn-shared-textrel");
 
-  for (const auto &Opt : ToolChain.ExtraOpts)
-    CmdArgs.push_back(Opt.c_str());
+  ToolChain.addExtraOpts(CmdArgs);
 
   CmdArgs.push_back("--eh-frame-hdr");
 

clang/lib/Driver/ToolChains/Gnu.h

@@ -356,6 +356,12 @@ class LLVM_LIBRARY_VISIBILITY Generic_ELF : public Generic_GCC {
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind DeviceOffloadKind) const override;
+
+  virtual std::string getDynamicLinker(const llvm::opt::ArgList &Args) const {
+    return {};
+  }
+
+  virtual void addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {}
 };
 
 } // end namespace toolchains

clang/lib/Driver/ToolChains/Hurd.cpp

@@ -61,8 +61,7 @@ static StringRef getOSLibDir(const llvm::Triple &Triple, const ArgList &Args) {
   return Triple.isArch32Bit() ? "lib" : "lib64";
 }
 
-Hurd::Hurd(const Driver &D, const llvm::Triple &Triple,
-           const ArgList &Args)
+Hurd::Hurd(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
     : Generic_ELF(D, Triple, Args) {
   std::string SysRoot = computeSysRoot();
   path_list &Paths = getFilePaths();
@@ -170,3 +169,8 @@ void Hurd::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
 
   addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
 }
+
+void Hurd::addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {
+  for (const auto &Opt : ExtraOpts)
+    CmdArgs.push_back(Opt.c_str());
+}

clang/lib/Driver/ToolChains/Hurd.h

@@ -27,9 +27,11 @@ class LLVM_LIBRARY_VISIBILITY Hurd : public Generic_ELF {
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
-  virtual std::string computeSysRoot() const;
+  std::string computeSysRoot() const;
 
-  virtual std::string getDynamicLinker(const llvm::opt::ArgList &Args) const;
+  std::string getDynamicLinker(const llvm::opt::ArgList &Args) const override;
+
+  void addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const override;
 
   std::vector<std::string> ExtraOpts;
 

clang/lib/Driver/ToolChains/Linux.cpp

@@ -1007,3 +1007,8 @@ llvm::DenormalMode Linux::getDefaultDenormalModeForType(
     return llvm::DenormalMode::getIEEE();
   }
 }
+
+void Linux::addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {
+  for (const auto &Opt : ExtraOpts)
+    CmdArgs.push_back(Opt.c_str());
+}

clang/lib/Driver/ToolChains/Linux.h

@@ -42,7 +42,9 @@ class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF {
                         llvm::opt::ArgStringList &CmdArgs) const override;
   virtual std::string computeSysRoot() const;
 
-  virtual std::string getDynamicLinker(const llvm::opt::ArgList &Args) const;
+  std::string getDynamicLinker(const llvm::opt::ArgList &Args) const override;
+
+  void addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const override;
 
   std::vector<std::string> ExtraOpts;