Introduce -nostdlib++ flag to disable linking the C++ standard library.

[thakis]

Summary

Projects that want to statically link their own C++ standard library currently need to pass -nostdlib or -nodefaultlibs, which also disables linking of the builtins library, -lm, and so on. Alternatively, they could use clang instead of clang++, but that already disables implicit addition of -lm on some toolchains.

Add a dedicated flag -nostdlib++ that disables just linking of libc++ / libstdc++. This is analogous to -nostdinc++.

[thakis]

Most of the patch is unifying all the toolchains to call the newly-introduced ToolChain::ShouldLinkCXXStdlib() instead of all manually checking for D.CCIsCXX() && !getFlag(nostdlib, nodefaultlibs). The actual behavior change is to make that function check the new nostdlib++ flag too.

One use-case for this new flag is https://cs.chromium.org/chromium/src/build/config/c%2B%2B/BUILD.gn?type=cs&q=nodefaultlibs&sq=package:chromium&l=32

[joerg]

I don't really like this. The reason why -lm is added explicitly on many targets is because the C++ STL typically depends on it and that means for static linking and broken ELF linkers, it will be necessary to link against it explicitly.
There is also the question on whether any platform we have currently uses separate STL and ABI libraries and it is not clear whether the flag should handle both.

[hans]

This seems reasonable to me.

lib/Driver/ToolChain.cpp

660

The message here doesn't really add any info. I think asserting without a message in this case is fine.

[thakis]

r308997, thanks!

[thakis]

Sounds like this ended up being useful for Android too: https://github.com/android-ndk/ndk/issues/105#issuecomment-324179958

[thakis]

Also useful for random other projects on github: https://github.com/mapbox/mason/pull/545#issuecomment-367082479

GCC also added support for this flag: https://github.com/gcc-mirror/gcc/commit/fc2fb4fd547fb39d76237a3a1a50f5c4f3646936

include/clang/Driver/Options.td

 def noprebind : Flag<["-"], "noprebind">;
 def noseglinkedit : Flag<["-"], "noseglinkedit">;
 def nostartfiles : Flag<["-"], "nostartfiles">;
 def nostdinc : Flag<["-"], "nostdinc">, Flags<[CoreOption]>;
 def nostdlibinc : Flag<["-"], "nostdlibinc">;
 def nostdincxx : Flag<["-"], "nostdinc++">, Flags<[CC1Option]>,
   HelpText<"Disable standard #include directories for the C++ standard library">;
 def nostdlib : Flag<["-"], "nostdlib">;
+def nostdlibxx : Flag<["-"], "nostdlib++">;
 def object : Flag<["-"], "object">;
 def o : JoinedOrSeparate<["-"], "o">, Flags<[DriverOption, RenderAsInput, CC1Option, CC1AsOption]>,
   HelpText<"Write output to <file>">, MetaVarName<"<file>">;
 def pagezero__size : JoinedOrSeparate<["-"], "pagezero_size">;
 def pass_exit_codes : Flag<["-", "--"], "pass-exit-codes">, Flags<[Unsupported]>;
 def pedantic_errors : Flag<["-", "--"], "pedantic-errors">, Group<pedantic_Group>, Flags<[CC1Option]>;
 def pedantic : Flag<["-", "--"], "pedantic">, Group<pedantic_Group>, Flags<[CC1Option]>;
 def pg : Flag<["-"], "pg">, HelpText<"Enable mcount instrumentation">, Flags<[CC1Option]>;

include/clang/Driver/ToolChain.h

public:
   virtual CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const;
 
   /// AddClangCXXStdlibIncludeArgs - Add the clang -cc1 level arguments to set
   /// the include paths to use for the given C++ standard library type.
   virtual void
   AddClangCXXStdlibIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                                llvm::opt::ArgStringList &CC1Args) const;
 
+  /// Returns if the C++ standard library should be linked in.
+  /// Note that e.g. -lm should still be linked even if this returns false.
+  bool ShouldLinkCXXStdlib(const llvm::opt::ArgList &Args) const;
+
   /// AddCXXStdlibLibArgs - Add the system specific linker arguments to use
   /// for the given C++ standard library type.
   virtual void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                                    llvm::opt::ArgStringList &CmdArgs) const;
 
   /// AddFilePathLibArgs - Add each thing in getFilePaths() as a "-L" option.
   void AddFilePathLibArgs(const llvm::opt::ArgList &Args,
                           llvm::opt::ArgStringList &CmdArgs) const;

lib/Driver/ToolChain.cpp

void ToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
   //
   // While it is being called, replicate a bit of a hack to propagate the
   // '-stdlib=' flag down to CC1 so that it can in turn customize the C++
   // header search paths with it. Once all systems are overriding this
   // function, the CC1 flag and this line can be removed.
   DriverArgs.AddAllArgs(CC1Args, options::OPT_stdlib_EQ);
 }
 
+bool ToolChain::ShouldLinkCXXStdlib(const llvm::opt::ArgList &Args) const {
+  return getDriver().CCCIsCXX() &&
+         !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs,
+                      options::OPT_nostdlibxx);
+}
+
 void ToolChain::AddCXXStdlibLibArgs(const ArgList &Args,
                                     ArgStringList &CmdArgs) const {
+  assert(!Args.hasArg(options::OPT_nostdlibxx) &&
+         "should not have called this");
   CXXStdlibType Type = GetCXXStdlibType(Args);
 
   switch (Type) {
   case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
     break;
 
   case ToolChain::CST_Libstdcxx:

lib/Driver/ToolChains/Ananas.cpp

Args.AddAllArgs(CmdArgs,
                   {options::OPT_T_Group, options::OPT_e, options::OPT_s,
                    options::OPT_t, options::OPT_Z_Flag, options::OPT_r});
 
   if (D.isUsingLTO())
     AddGoldPlugin(ToolChain, Args, CmdArgs, D.getLTOMode() == LTOK_Thin, D);
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (D.CCCIsCXX())
-      ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
+  if (ToolChain.ShouldLinkCXXStdlib(Args))
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs))
     CmdArgs.push_back("-lc");
-  }
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtend.o")));
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtn.o")));
   }
 
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
   C.addCommand(llvm::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs));

lib/Driver/ToolChains/BareMetal.cpp

void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   CmdArgs.push_back("-Bstatic");
 
   CmdArgs.push_back(Args.MakeArgString("-L" + TC.getRuntimesDir()));
 
   Args.AddAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_e, options::OPT_s, options::OPT_t,
                             options::OPT_Z_Flag, options::OPT_r});
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (C.getDriver().CCCIsCXX())
-      TC.AddCXXStdlibLibArgs(Args, CmdArgs);
-
+  if (TC.ShouldLinkCXXStdlib(Args))
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lm");
 
     TC.AddLinkRuntimeLib(Args, CmdArgs);
   }
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 
   C.addCommand(llvm::make_unique<Command>(JA, *this,
                                           Args.MakeArgString(TC.GetLinkerPath()),
                                           CmdArgs, Inputs));
 }

lib/Driver/ToolChains/CloudABI.cpp

Args.AddAllArgs(CmdArgs,
                   {options::OPT_T_Group, options::OPT_e, options::OPT_s,
                    options::OPT_t, options::OPT_Z_Flag, options::OPT_r});
 
   if (D.isUsingLTO())
     AddGoldPlugin(ToolChain, Args, CmdArgs, D.getLTOMode() == LTOK_Thin, D);
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (D.CCCIsCXX())
-      ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
+  if (ToolChain.ShouldLinkCXXStdlib(Args))
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lcompiler_rt");
   }
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtend.o")));
 
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());

lib/Driver/ToolChains/CommonArgs.cpp

collectSanitizerRuntimes(const ToolChain &TC, const ArgList &Args,
   }
   if (SanArgs.needsEsanRt())
     StaticRuntimes.push_back("esan");
 }
 
 static void addLibFuzzerRuntime(const ToolChain &TC,
                                 const ArgList &Args,
                                 ArgStringList &CmdArgs) {
-    StringRef ParentDir = llvm::sys::path::parent_path(TC.getDriver().InstalledDir);
-    SmallString<128> P(ParentDir);
-    llvm::sys::path::append(P, "lib", "libLLVMFuzzer.a");
-    CmdArgs.push_back(Args.MakeArgString(P));
+  StringRef ParentDir =
+      llvm::sys::path::parent_path(TC.getDriver().InstalledDir);
+  if (!Args.hasArg(clang::driver::options::OPT_nostdlibxx))
     TC.AddCXXStdlibLibArgs(Args, CmdArgs);
 }
 
 
 // Should be called before we add system libraries (C++ ABI, libstdc++/libc++,
 // C runtime, etc). Returns true if sanitizer system deps need to be linked in.
 bool tools::addSanitizerRuntimes(const ToolChain &TC, const ArgList &Args,
                                  ArgStringList &CmdArgs) {

lib/Driver/ToolChains/CrossWindows.cpp

if (Args.hasArg(options::OPT_shared) || Args.hasArg(options::OPT_rdynamic)) {
     CmdArgs.push_back("--out-implib");
     CmdArgs.push_back(Args.MakeArgString(ImpLib));
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   TC.AddFilePathLibArgs(Args, CmdArgs);
   AddLinkerInputs(TC, Inputs, Args, CmdArgs, JA);
 
-  if (D.CCCIsCXX() && !Args.hasArg(options::OPT_nostdlib) &&
-      !Args.hasArg(options::OPT_nodefaultlibs)) {
+  if (TC.ShouldLinkCXXStdlib(Args)) {
     bool StaticCXX = Args.hasArg(options::OPT_static_libstdcxx) &&
                      !Args.hasArg(options::OPT_static);
     if (StaticCXX)
       CmdArgs.push_back("-Bstatic");
     TC.AddCXXStdlibLibArgs(Args, CmdArgs);
     if (StaticCXX)
       CmdArgs.push_back("-Bdynamic");
   }

lib/Driver/ToolChains/Darwin.cpp

void darwin::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (unsigned Parallelism =
           getLTOParallelism(Args, getToolChain().getDriver())) {
     CmdArgs.push_back("-mllvm");
     CmdArgs.push_back(
         Args.MakeArgString(Twine("-threads=") + llvm::to_string(Parallelism)));
   }
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (getToolChain().getDriver().CCCIsCXX())
-      getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
-
+  if (getToolChain().ShouldLinkCXXStdlib(Args))
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     // link_ssp spec is empty.
 
     // Let the tool chain choose which runtime library to link.
     getMachOToolChain().AddLinkRuntimeLibArgs(Args, CmdArgs);
 
     // No need to do anything for pthreads. Claim argument to avoid warning.
     Args.ClaimAllArgs(options::OPT_pthread);
     Args.ClaimAllArgs(options::OPT_pthreads);

lib/Driver/ToolChains/DragonFly.cpp

if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     CmdArgs.push_back("-L/usr/lib/gcc50");
 
     if (!Args.hasArg(options::OPT_static)) {
       CmdArgs.push_back("-rpath");
       CmdArgs.push_back("/usr/lib/gcc50");
     }
 
     if (D.CCCIsCXX()) {
+      if (getToolChain().ShouldLinkCXXStdlib(Args))
         getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
       CmdArgs.push_back("-lm");
     }
 
     if (Args.hasArg(options::OPT_pthread))
       CmdArgs.push_back("-lpthread");
 
     if (!Args.hasArg(options::OPT_nolibc)) {
       CmdArgs.push_back("-lc");

lib/Driver/ToolChains/FreeBSD.cpp

if (D.isUsingLTO())
     AddGoldPlugin(ToolChain, Args, CmdArgs, D.getLTOMode() == LTOK_Thin, D);
 
   bool NeedsSanitizerDeps = addSanitizerRuntimes(ToolChain, Args, CmdArgs);
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     addOpenMPRuntime(CmdArgs, ToolChain, Args);
     if (D.CCCIsCXX()) {
+      if (ToolChain.ShouldLinkCXXStdlib(Args))
         ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
       if (Args.hasArg(options::OPT_pg))
         CmdArgs.push_back("-lm_p");
       else
         CmdArgs.push_back("-lm");
     }
     if (NeedsSanitizerDeps)
       linkSanitizerRuntimeDeps(ToolChain, CmdArgs);
     // FIXME: For some reason GCC passes -lgcc and -lgcc_s before adding

lib/Driver/ToolChains/Fuchsia.cpp

void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     if (Args.hasArg(options::OPT_static))
       CmdArgs.push_back("-Bdynamic");
 
     if (D.CCCIsCXX()) {
+      if (ToolChain.ShouldLinkCXXStdlib(Args)) {
         bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
                                    !Args.hasArg(options::OPT_static);
         if (OnlyLibstdcxxStatic)
           CmdArgs.push_back("-Bstatic");
         ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
         if (OnlyLibstdcxxStatic)
           CmdArgs.push_back("-Bdynamic");
+      }
       CmdArgs.push_back("-lm");
     }
 
     AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
 
     if (Args.hasArg(options::OPT_pthread) ||
         Args.hasArg(options::OPT_pthreads))
       CmdArgs.push_back("-lpthread");

lib/Driver/ToolChains/Gnu.cpp

void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   bool NeedsSanitizerDeps = addSanitizerRuntimes(ToolChain, Args, CmdArgs);
   bool NeedsXRayDeps = addXRayRuntime(ToolChain, Args, CmdArgs);
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
   // The profile runtime also needs access to system libraries.
   getToolChain().addProfileRTLibs(Args, CmdArgs);
 
   if (D.CCCIsCXX() &&
       !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
+    if (ToolChain.ShouldLinkCXXStdlib(Args)) {
       bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
                                  !Args.hasArg(options::OPT_static);
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bstatic");
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bdynamic");
+    }
     CmdArgs.push_back("-lm");
   }
   // Silence warnings when linking C code with a C++ '-stdlib' argument.
   Args.ClaimAllArgs(options::OPT_stdlib_EQ);
 
   if (!Args.hasArg(options::OPT_nostdlib)) {
     if (!Args.hasArg(options::OPT_nodefaultlibs)) {
       if (Args.hasArg(options::OPT_static))

lib/Driver/ToolChains/Hexagon.cpp

constructHexagonLinkArgs(Compilation &C, const JobAction &JA,
 
   AddLinkerInputs(HTC, Inputs, Args, CmdArgs, JA);
 
   //----------------------------------------------------------------------------
   // Libraries
   //----------------------------------------------------------------------------
   if (IncStdLib && IncDefLibs) {
     if (D.CCCIsCXX()) {
+      if (HTC.ShouldLinkCXXStdlib(Args))
         HTC.AddCXXStdlibLibArgs(Args, CmdArgs);
       CmdArgs.push_back("-lm");
     }
 
     CmdArgs.push_back("--start-group");
 
     if (!IsShared) {
       for (const std::string &Lib : OsLibs)
         CmdArgs.push_back(Args.MakeArgString("-l" + Lib));

lib/Driver/ToolChains/MinGW.cpp

void tools::MinGW::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   TC.AddFilePathLibArgs(Args, CmdArgs);
   AddLinkerInputs(TC, Inputs, Args, CmdArgs, JA);
 
   // TODO: Add ASan stuff here
 
   // TODO: Add profile stuff here
 
-  if (D.CCCIsCXX() &&
-      !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
+  if (TC.ShouldLinkCXXStdlib(Args)) {
     bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
                                !Args.hasArg(options::OPT_static);
     if (OnlyLibstdcxxStatic)
       CmdArgs.push_back("-Bstatic");
     TC.AddCXXStdlibLibArgs(Args, CmdArgs);
     if (OnlyLibstdcxxStatic)
       CmdArgs.push_back("-Bdynamic");
   }

lib/Driver/ToolChains/Minix.cpp

Args.AddAllArgs(CmdArgs,
                   {options::OPT_L, options::OPT_T_Group, options::OPT_e});
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);
 
   getToolChain().addProfileRTLibs(Args, CmdArgs);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     if (D.CCCIsCXX()) {
+      if (getToolChain().ShouldLinkCXXStdlib(Args))
         getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
       CmdArgs.push_back("-lm");
     }
   }
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
     if (Args.hasArg(options::OPT_pthread))
       CmdArgs.push_back("-lpthread");
     CmdArgs.push_back("-lc");

lib/Driver/ToolChains/NaCl.cpp

void nacltools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Args.hasArg(options::OPT_Z_Xlinker__no_demangle))
     CmdArgs.push_back("--no-demangle");
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (D.CCCIsCXX() &&
       !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
+    if (ToolChain.ShouldLinkCXXStdlib(Args)) {
       bool OnlyLibstdcxxStatic =
           Args.hasArg(options::OPT_static_libstdcxx) && !IsStatic;
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bstatic");
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
       if (OnlyLibstdcxxStatic)
         CmdArgs.push_back("-Bdynamic");
+    }
     CmdArgs.push_back("-lm");
   }
 
   if (!Args.hasArg(options::OPT_nostdlib)) {
     if (!Args.hasArg(options::OPT_nodefaultlibs)) {
       // Always use groups, since it has no effect on dynamic libraries.
       CmdArgs.push_back("--start-group");
       CmdArgs.push_back("-lc");

lib/Driver/ToolChains/NetBSD.cpp

if (Major >= 7 || Major == 0) {
     default:
       break;
     }
   }
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     addOpenMPRuntime(CmdArgs, getToolChain(), Args);
     if (D.CCCIsCXX()) {
+      if (getToolChain().ShouldLinkCXXStdlib(Args))
         getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
       CmdArgs.push_back("-lm");
     }
     if (NeedsSanitizerDeps)
       linkSanitizerRuntimeDeps(getToolChain(), CmdArgs);
     if (Args.hasArg(options::OPT_pthread))
       CmdArgs.push_back("-lpthread");
     CmdArgs.push_back("-lc");
 

lib/Driver/ToolChains/OpenBSD.cpp

void openbsd::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_e, options::OPT_s, options::OPT_t,
                             options::OPT_Z_Flag, options::OPT_r});
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     if (D.CCCIsCXX()) {
+      if (getToolChain().ShouldLinkCXXStdlib(Args))
         getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
       if (Args.hasArg(options::OPT_pg))
         CmdArgs.push_back("-lm_p");
       else
         CmdArgs.push_back("-lm");
     }
 
     // FIXME: For some reason GCC passes -lgcc before adding
     // the default system libraries. Just mimic this for now.

lib/Driver/ToolChains/PS4CPU.cpp

static void ConstructGoldLinkJob(const Tool &T, Compilation &C,
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     // For PS4, we always want to pass libm, libstdc++ and libkernel
     // libraries for both C and C++ compilations.
     CmdArgs.push_back("-lkernel");
     if (D.CCCIsCXX()) {
+      if (ToolChain.ShouldLinkCXXStdlib(Args))
         ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
       if (Args.hasArg(options::OPT_pg))
         CmdArgs.push_back("-lm_p");
       else
         CmdArgs.push_back("-lm");
     }
     // FIXME: For some reason GCC passes -lgcc and -lgcc_s before adding
     // the default system libraries. Just mimic this for now.
     if (Args.hasArg(options::OPT_pg))

lib/Driver/ToolChains/Solaris.cpp

void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   getToolChain().AddFilePathLibArgs(Args, CmdArgs);
 
   Args.AddAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_e, options::OPT_r});
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (getToolChain().getDriver().CCCIsCXX())
+    if (getToolChain().ShouldLinkCXXStdlib(Args))
       getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
     CmdArgs.push_back("-lgcc_s");
     CmdArgs.push_back("-lc");
     if (!Args.hasArg(options::OPT_shared)) {
       CmdArgs.push_back("-lgcc");
       CmdArgs.push_back("-lm");
     }
   }

lib/Driver/ToolChains/WebAssembly.cpp

 
 void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                 const InputInfo &Output,
                                 const InputInfoList &Inputs,
                                 const ArgList &Args,
                                 const char *LinkingOutput) const {
 
   const ToolChain &ToolChain = getToolChain();
-  const Driver &D = ToolChain.getDriver();
   const char *Linker = Args.MakeArgString(ToolChain.GetLinkerPath());
   ArgStringList CmdArgs;
   CmdArgs.push_back("-flavor");
   CmdArgs.push_back("wasm");
 
   // Enable garbage collection of unused input sections by default, since code
   // size is of particular importance. This is significantly facilitated by
   // the enabling of -ffunction-sections and -fdata-sections in
else
       CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt1.o")));
 
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crti.o")));
   }
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
-    if (D.CCCIsCXX())
+    if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
 
     if (Args.hasArg(options::OPT_pthread))
       CmdArgs.push_back("-lpthread");
 
     CmdArgs.push_back("-allow-undefined-file");
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("wasm.syms")));
     CmdArgs.push_back("-lc");

test/Driver/nostdlibxx.cpp

+// RUN: %clangxx -target i686-pc-linux-gnu -### -nostdlib++ %s 2> %t
+// RUN: FileCheck < %t %s
+
+// We should still have -lm and the C standard libraries, but not -lstdc++.
+
+// CHECK-NOT: -lstdc++
+// CHECK-NOT: -lc++
+// CHECK: -lm