[CUDA] Allow targeting NVPTX directly without a host toolchain

[jhuber6]

Summary

Currently, the NVPTX compilation toolchain can only be invoked either
through CUDA or OpenMP via --offload-device-only. This is because we
cannot build a CUDA toolchain without an accompanying host toolchain for
the offloading. When using --target=nvptx64-nvidia-cuda this results
in generating calls to the GNU assembler and linker, leading to errors.

This patch abstracts the portions of the CUDA toolchain that are
independent of the host toolchain or offloading kind into a new base
class called NVPTXToolChain. We still need to read the host's triple
to build the CUDA installation, so if not present we just assume it will
match the host's system for now, or the user can provide the path
explicitly.

This should allow the compiler driver to create NVPTX device images
directly from C/C++ code.

[tra]

LGTM overall.

So, essentially the patch refactors what we've already been doing for OpenMP and made it usable manually, which will be useful for things like GPU-side libc tests.

clang/lib/Driver/ToolChains/Cuda.cpp

632–633

Nit: I'd just do it within the make_unique below. It should end up on a line by itself and should not hurt readability.

[jhuber6]

I just realized the method of copying the .o to a .cubin doesn't work if the link step is done in the same compilation because it doesn't exist yet. To fix this I could either make the tool chain emit .cubin if we're going straight to nvlink, or use a symbolic link. The former is uglier, the latter will probably only work on Linux.

Also do you think I should include the CUDA headers in with this? We can always get rid of them with nogpuinc or similar if they're not needed. The AMDGPU compilation still links in the device libraries so I'm wondering if we should at least be consistent.

[jdoerfert]

In D140158#3999716, @jhuber6 wrote:

Also do you think I should include the CUDA headers in with this? We can always get rid of them with nogpuinc or similar if they're not needed. The AMDGPU compilation still links in the device libraries so I'm wondering if we should at least be consistent.

For OpenMP at least we want this mode to include the device runtime and the respective native runtimes as well (except if we do LTO than both are included late).

[tra]

In D140158#3999716, @jhuber6 wrote:

I just realized the method of copying the .o to a .cubin doesn't work if the link step is done in the same compilation because it doesn't exist yet. To fix this I could either make the tool chain emit .cubin if we're going straight to nvlink, or use a symbolic link. The former is uglier, the latter will probably only work on Linux.

Does it have to be .cubin ? Does nvlink require it?

Also do you think I should include the CUDA headers in with this? We can always get rid of them with nogpuinc or similar if they're not needed. The AMDGPU compilation still links in the device libraries so I'm wondering if we should at least be consistent.

Only some CUDA headers can be used from C++ and they tend to contain host-only declarations, and stubs or CPU implementations of GPU-side functions in that case.
The rest rely on CUDA extensions, attributes, So, in this case doing a C++ compilation will give you a host-side view of the headers in the best case, which is not going to be particularly useful.

If we want to make GPU-side functions available, we'll need to have a pre-included wrapper with more preprocessor magic to make CUDA headers usable. Doing that in a C++ compilation would be questionable as for a C++ compilation a user would normally assume that no headers are pre-included by the compiler.

[jhuber6]

In D140158#3999783, @tra wrote:

In D140158#3999716, @jhuber6 wrote:

I just realized the method of copying the .o to a .cubin doesn't work if the link step is done in the same compilation because it doesn't exist yet. To fix this I could either make the tool chain emit .cubin if we're going straight to nvlink, or use a symbolic link. The former is uglier, the latter will probably only work on Linux.

Does it have to be .cubin ? Does nvlink require it?

Yes, it's one of the dumbest things in the CUDA toolchain. If the filename is a .o they assume it's a host file containing embedded RDC-code that needs to be combined. If it's a .cubin they assume it's device code. I have no clue why they couldn't just check the ELF flags, it's trivial.

Also do you think I should include the CUDA headers in with this? We can always get rid of them with nogpuinc or similar if they're not needed. The AMDGPU compilation still links in the device libraries so I'm wondering if we should at least be consistent.

Only some CUDA headers can be used from C++ and they tend to contain host-only declarations, and stubs or CPU implementations of GPU-side functions in that case.
The rest rely on CUDA extensions, attributes, So, in this case doing a C++ compilation will give you a host-side view of the headers in the best case, which is not going to be particularly useful.

If we want to make GPU-side functions available, we'll need to have a pre-included wrapper with more preprocessor magic to make CUDA headers usable. Doing that in a C++ compilation would be questionable as for a C++ compilation a user would normally assume that no headers are pre-included by the compiler.

We might want to at least include the libdevice files, most of our wrappers definitely won't work without CUDA or OpenMP language modes.

[JonChesterfield]

If we do magic header including, we should check for the freestanding argument and not include them with that set. I would prefer we not include cuda headers into C++ source that isn't being compiled as cuda, and also not link in misc cuda library files.

Anyone who has decided to compile raw c or c++ to ptx is doing something off the beaten path, I don't think we should assume they want implicit behaviour from other programming models thrown in.

[tra]

In D140158#3999810, @JonChesterfield wrote:

I don't think we should assume they want implicit behaviour from other programming models thrown in.

Agreed. Also, removing things is often surprisingly hard.
Let's keep things simlpe, get this compilation mode to the point where it's practically usable, see what we really want/need, and then make those common cases the default or easier to use.

As far as libdevice is concerned, it's only needed for sources that use CUDA headers, as those map the standard math functions to their implementations in libdevice. Stand-alone sources should not need it. We should also be able to compile libdevice.bc into a libdevice.o and then link with it, if needed, during the final executable link phase.

[jhuber6]

Addressing comments, I did the symbolic link method. It's a stupid hack that's only necessary because of nvlink's poor handling but I think this works around it well enough.

[jhuber6]

Fix format

[jhuber6]

Accidentally deleted the old getInputFilename routine which we need. The
symlink worked fine but would break on Windows, so I ended up writing a hack
that would only use .cubin if we have the nvlink linker active and the input
comes from the assembler. It's extremely ugly so let me know what you think.

[jhuber6]

Updating. Used a different method to determine if we need to use .cubin or .o. It's a little ugly but I don't think there's a better way to do it.

Also I just realized that if this goes through I could probably heavily simplify linker wrapper code by just invoking clang --target=nvptx64 instead of calling the tools manually. So that's another benefit to this.

[jdoerfert]

FWIW, creating CUBIN from C/C++ directly would be really useful when debugging (and in combination with our soon to be available JIT object loader).

@tra Can we get this in somehow?

[tra]

LGTM overall, with few nits.

clang/lib/Driver/ToolChains/Cuda.cpp

448–450

Can't say that I like this approach. It heavily relies on "happens to work".

Perhaps a better way to deal with this is to create the temporary GPU object file name with ".cubin" extension to start with.

450

typo: getInputFilename

469

Nit: I'd add an else { Relocatable = false; // comment on what use cases use relocatable compilation by default. } and leave it uninitialized here. At the very least it may be worth a comment. Silently defaulting to true makes me ask "what other compilation modes we may have?" and stand-alone compilation targeting NVPTX is hard to infer here from the surrounding details.

clang/lib/Driver/ToolChains/Cuda.h

196–197

Nit: it's hard to tell whether the whitespace additions are spaces or tabs. They show up as ">" to me which suggests it may be tabs. Just in case it is indeed the case, please make sure to un-tabify the changes.

clang/test/Driver/cuda-cross-compiling.c

37–38

This may fail on windows where ptxas/nvlink will be ptxas.exe nvlink.exe. I think we typically use something like fatbinary{{.*}}" in other tests.

[jhuber6]

clang/lib/Driver/ToolChains/Cuda.cpp

448–450

As far as I know, the files are created independently of the tool-chains so I'm not sure if we'd be able to check there. The current way is to use getInputFilename but that doesn't have access to the compilation. As far as I can come up with there's the following solutions

• Do this and check the temp files
• Create a symbolic link if the file is empty (Doesn't work on Windows)
• Make a random global that's true if the Linker tool was built at some point

469

Works for me.

clang/test/Driver/cuda-cross-compiling.c

37–38

Good point.

[jhuber6]

clang/lib/Driver/ToolChains/Cuda.h

196–197

I think it's because the original file was formatted incorrectly, so all my new changes are formatted correctly. I'm somewhat more tempted to just clang-format it upstream and rebase it.

[jhuber6]

Addressing some comments. I don't know if there's a cleaner way to mess around with the .cubin nonsense. I liked symbolic links but that doesn't work on Windows.

[tra]

LGTM with few minor nits and questions.

In D140158#4063689, @jhuber6 wrote:

Addressing some comments. I don't know if there's a cleaner way to mess around with the .cubin nonsense. I liked symbolic links but that doesn't work on Windows.

Can we do a copy or rename instead. That could be more portable.

clang/lib/Driver/ToolChains/Cuda.cpp

448–450

Naming is hard. :-(

OK, let's add a FIXME to this comment and hope to get it fixed when NVIDIA's tools become less obsessive about file extensions. I'll file a bug with them to get the ball rolling on their end.

515–518

Nit: Looks like there are tabs.

clang/lib/Driver/ToolChains/Cuda.h

196–197

Clang-formatting the file(s) and submitting that change separately before the patch SGTM.

[jhuber6]

In D140158#4063720, @tra wrote:

LGTM with few minor nits and questions.

In D140158#4063689, @jhuber6 wrote:

Addressing some comments. I don't know if there's a cleaner way to mess around with the .cubin nonsense. I liked symbolic links but that doesn't work on Windows.

Can we do a copy or rename instead. That could be more portable.

I do a copy in this patch already. The problem is that if it's an internal link, e.g. clang --target=nvptx64-nvidia-cuda foo.c bar.c, then there will be no file to copy. The symbol link got around this by linking the files so once the .o was written the contents would automatically appear in the .cubin. The other approach is to detect this and use the correct names which is what this patch does, albeit a little jankily.

clang/lib/Driver/ToolChains/Cuda.cpp

448–450

I would like that. it's a very simple check if you actually know how ELF headers work... Also while you're at it, ask for how they set their machine flags in Nvidia so we can display the arch via llvm-readelf.

I'll add some FIXME's.

515–518

I think that's just the diff showing that it was indented, there's no tabs in the file.

clang/lib/Driver/ToolChains/Cuda.h

196–197

Already did :)

[alexfh]

This patch breaks our cuda compilations. The output file isn't created after it:

$ echo 'extern "C" __attribute__((global)) void q() {}' >q.cc
$ good-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-good.o \
  && bad-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-bad.o \
  && ls qqq*.o
qqq-good.o

[jhuber6]

In D140158#4082789, @alexfh wrote:

This patch breaks our cuda compilations. The output file isn't created after it:

$ echo 'extern "C" __attribute__((global)) void q() {}' >q.cc
$ good-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-good.o \
  && bad-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-bad.o \
  && ls qqq*.o
qqq-good.o

https://github.com/llvm/llvm-project/issues/60301 Still broken after this fix?

[alexfh]

In D140158#4082804, @jhuber6 wrote:

In D140158#4082789, @alexfh wrote:

This patch breaks our cuda compilations. The output file isn't created after it:

$ echo 'extern "C" __attribute__((global)) void q() {}' >q.cc
$ good-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-good.o \
  && bad-clang \
    -nocudainc -x cuda \
    --cuda-path=somepath/cuda/ \
    -Wno-unknown-cuda-version --cuda-device-only \
    -c q.cc -o qqq-bad.o \
  && ls qqq*.o
qqq-good.o

https://github.com/llvm/llvm-project/issues/60301 Still broken after this fix?

That works. Thanks!

clang/lib/Driver/Driver.cpp

case llvm::Triple::NaCl:
       TC = std::make_unique<toolchains::NaClToolChain>(*this, Target, Args);
       break;
     case llvm::Triple::Fuchsia:
       TC = std::make_unique<toolchains::Fuchsia>(*this, Target, Args);
       break;
     case llvm::Triple::Solaris:
       TC = std::make_unique<toolchains::Solaris>(*this, Target, Args);
       break;
+    case llvm::Triple::CUDA:
+      TC = std::make_unique<toolchains::NVPTXToolChain>(*this, Target, Args);
+      break;
     case llvm::Triple::AMDHSA:
       TC = std::make_unique<toolchains::ROCMToolChain>(*this, Target, Args);
       break;
     case llvm::Triple::AMDPAL:
     case llvm::Triple::Mesa3D:
       TC = std::make_unique<toolchains::AMDGPUToolChain>(*this, Target, Args);
       break;
     case llvm::Triple::Win32:
default:
         else if (Target.isOSBinFormatMachO())
           TC = std::make_unique<toolchains::MachO>(*this, Target, Args);
         else
           TC = std::make_unique<toolchains::Generic_GCC>(*this, Target, Args);
       }
     }
   }
 
-  // Intentionally omitted from the switch above: llvm::Triple::CUDA.  CUDA
-  // compiles always need two toolchains, the CUDA toolchain and the host
-  // toolchain.  So the only valid way to create a CUDA toolchain is via
-  // CreateOffloadingDeviceToolChains.
-
   return *TC;
 }
 
 const ToolChain &Driver::getOffloadingDeviceToolChain(
     const ArgList &Args, const llvm::Triple &Target, const ToolChain &HostTC,
     const Action::OffloadKind &TargetDeviceOffloadKind) const {
   // Use device / host triples as the key into the ToolChains map because the
   // device ToolChain we create depends on both.

clang/lib/Driver/ToolChains/Cuda.h

public:
    void ConstructJob(Compilation &C, const JobAction &JA,
                      const InputInfo &Output, const InputInfoList &Inputs,
                      const llvm::opt::ArgList &TCArgs,
                      const char *LinkingOutput) const override;
 };
 
 // Runs fatbinary, which combines GPU object files ("cubin" files) and/or PTX
 // assembly into a single output file.
+class LLVM_LIBRARY_VISIBILITY FatBinary : public Tool {
+ public:
+   FatBinary(const ToolChain &TC) : Tool("NVPTX::Linker", "fatbinary", TC) {}
+
+   bool hasIntegratedCPP() const override { return false; }
+
+   void ConstructJob(Compilation &C, const JobAction &JA,
+                     const InputInfo &Output, const InputInfoList &Inputs,
+                     const llvm::opt::ArgList &TCArgs,
+                     const char *LinkingOutput) const override;
+};
+
+// Runs nvlink, which links GPU object files ("cubin" files) into a single file.
 class LLVM_LIBRARY_VISIBILITY Linker : public Tool {
  public:
-   Linker(const ToolChain &TC) : Tool("NVPTX::Linker", "fatbinary", TC) {}
+   Linker(const ToolChain &TC) : Tool("NVPTX::Linker", "nvlink", TC) {}
 
    bool hasIntegratedCPP() const override { return false; }
 
    void ConstructJob(Compilation &C, const JobAction &JA,
                      const InputInfo &Output, const InputInfoList &Inputs,
                      const llvm::opt::ArgList &TCArgs,
                      const char *LinkingOutput) const override;
 };
 
 void getNVPTXTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                             const llvm::opt::ArgList &Args,
                             std::vector<StringRef> &Features);
 
 } // end namespace NVPTX
 } // end namespace tools
 
 namespace toolchains {
 
-class LLVM_LIBRARY_VISIBILITY CudaToolChain : public ToolChain {
+class LLVM_LIBRARY_VISIBILITY NVPTXToolChain : public ToolChain {
  public:
-  CudaToolChain(const Driver &D, const llvm::Triple &Triple,
-                const ToolChain &HostTC, const llvm::opt::ArgList &Args);
-
-  const llvm::Triple *getAuxTriple() const override {
-    return &HostTC.getTriple();
-  }
+   NVPTXToolChain(const Driver &D, const llvm::Triple &Triple,
+                  const llvm::Triple &HostTriple,
+                  const llvm::opt::ArgList &Args);
 
-  std::string getInputFilename(const InputInfo &Input) const override;
+   NVPTXToolChain(const Driver &D, const llvm::Triple &Triple,
+                  const llvm::opt::ArgList &Args);
 
    llvm::opt::DerivedArgList *
    TranslateArgs(const llvm::opt::DerivedArgList &Args, StringRef BoundArch,
                  Action::OffloadKind DeviceOffloadKind) const override;
-  void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
-                             llvm::opt::ArgStringList &CC1Args,
-                             Action::OffloadKind DeviceOffloadKind) const override;
-
-  llvm::DenormalMode getDefaultDenormalModeForType(
-      const llvm::opt::ArgList &DriverArgs, const JobAction &JA,
-      const llvm::fltSemantics *FPType = nullptr) const override;
 
-  // Never try to use the integrated assembler with CUDA; always fork out to
+   // Never try to use the integrated assembler with NVPTX; always fork out to
    // ptxas.
    bool useIntegratedAs() const override { return false; }
    bool isCrossCompiling() const override { return true; }
    bool isPICDefault() const override { return false; }
    bool isPIEDefault(const llvm::opt::ArgList &Args) const override {
     return false;
    }
    bool isPICDefaultForced() const override { return false; }
    bool SupportsProfiling() const override { return false; }
+
+   bool IsMathErrnoDefault() const override { return false; }
+
    bool supportsDebugInfoOption(const llvm::opt::Arg *A) const override;
    void adjustDebugInfoKind(codegenoptions::DebugInfoKind &DebugInfoKind,
                             const llvm::opt::ArgList &Args) const override;
-  bool IsMathErrnoDefault() const override { return false; }
+
+   // NVPTX supports only DWARF2.
+   unsigned GetDefaultDwarfVersion() const override { return 2; }
+   unsigned getMaxDwarfVersion() const override { return 2; }
+
+   CudaInstallationDetector CudaInstallation;
+
+ protected:
+   Tool *buildAssembler() const override; // ptxas.
+   Tool *buildLinker() const override;    // nvlink.
+};
+
+class LLVM_LIBRARY_VISIBILITY CudaToolChain : public NVPTXToolChain {
+ public:
+   CudaToolChain(const Driver &D, const llvm::Triple &Triple,
+                 const ToolChain &HostTC, const llvm::opt::ArgList &Args);
+
+   const llvm::Triple *getAuxTriple() const override {
+    return &HostTC.getTriple();
+   }
+
+   std::string getInputFilename(const InputInfo &Input) const override;
+
+   llvm::opt::DerivedArgList *
+   TranslateArgs(const llvm::opt::DerivedArgList &Args, StringRef BoundArch,
+                 Action::OffloadKind DeviceOffloadKind) const override;
+   void
+   addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
+                         llvm::opt::ArgStringList &CC1Args,
+                         Action::OffloadKind DeviceOffloadKind) const override;
+
+   llvm::DenormalMode getDefaultDenormalModeForType(
+       const llvm::opt::ArgList &DriverArgs, const JobAction &JA,
+       const llvm::fltSemantics *FPType = nullptr) const override;
 
    void AddCudaIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
 
-  void addClangWarningOptions(llvm::opt::ArgStringList &CC1Args) const override;
-  CXXStdlibType GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
+   void
+   addClangWarningOptions(llvm::opt::ArgStringList &CC1Args) const override;
+   CXXStdlibType
+   GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
    void
    AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args) const override;
    void AddClangCXXStdlibIncludeArgs(
        const llvm::opt::ArgList &Args,
        llvm::opt::ArgStringList &CC1Args) const override;
    void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
    SanitizerMask getSupportedSanitizers() const override;
 
    VersionTuple
    computeMSVCVersion(const Driver *D,
                       const llvm::opt::ArgList &Args) const override;
 
-  unsigned GetDefaultDwarfVersion() const override { return 2; }
-  // NVPTX supports only DWARF2.
-  unsigned getMaxDwarfVersion() const override { return 2; }
-
    const ToolChain &HostTC;
-  CudaInstallationDetector CudaInstallation;
 
    /// Uses nvptx-arch tool to get arch of the system GPU. Will return error
    /// if unable to find one.
    virtual Expected<SmallVector<std::string>>
    getSystemGPUArchs(const llvm::opt::ArgList &Args) const override;
 
  protected:
-  Tool *buildAssembler() const override;  // ptxas
-  Tool *buildLinker() const override;     // fatbinary (ok, not really a linker)
+   Tool *buildAssembler() const override; // ptxas
+   Tool *buildLinker() const override;    // fatbinary (ok, not really a linker)
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_CUDA_H

clang/lib/Driver/ToolChains/Cuda.cpp

 }
 
 void NVPTX::Assembler::ConstructJob(Compilation &C, const JobAction &JA,
                                     const InputInfo &Output,
                                     const InputInfoList &Inputs,
                                     const ArgList &Args,
                                     const char *LinkingOutput) const {
   const auto &TC =
-      static_cast<const toolchains::CudaToolChain &>(getToolChain());
+      static_cast<const toolchains::NVPTXToolChain &>(getToolChain());
   assert(TC.getTriple().isNVPTX() && "Wrong platform");
 
   StringRef GPUArchName;
-  // If this is an OpenMP action we need to extract the device architecture
-  // from the -march=arch option. This option may come from -Xopenmp-target
-  // flag or the default value.
-  if (JA.isDeviceOffloading(Action::OFK_OpenMP)) {
+  // If this is a CUDA action we need to extract the device architecture
+  // from the Job's associated architecture, otherwise use the -march=arch
+  // option. This option may come from -Xopenmp-target flag or the default
+  // value.
+  if (JA.isDeviceOffloading(Action::OFK_Cuda)) {
+    GPUArchName = JA.getOffloadingArch();
+  } else {
     GPUArchName = Args.getLastArgValue(options::OPT_march_EQ);
     assert(!GPUArchName.empty() && "Must have an architecture passed in.");
-  } else
-    GPUArchName = JA.getOffloadingArch();
+  }
 
   // Obtain architecture from the action.
   CudaArch gpu_arch = StringToCudaArch(GPUArchName);
   assert(gpu_arch != CudaArch::UNKNOWN &&
          "Device action expected to have an architecture.");
 
   // Check that our installation's ptxas supports gpu_arch.
   if (!Args.hasArg(options::OPT_no_cuda_version_check)) {
void NVPTX::Assembler::ConstructJob(Compilation &C, const JobAction &JA,
   // Pass -v to ptxas if it was passed to the driver.
   if (Args.hasArg(options::OPT_v))
     CmdArgs.push_back("-v");
 
   CmdArgs.push_back("--gpu-name");
   CmdArgs.push_back(Args.MakeArgString(CudaArchToString(gpu_arch)));
   CmdArgs.push_back("--output-file");
   const char *OutputFileName = Args.MakeArgString(TC.getInputFilename(Output));
-  if (std::string(OutputFileName) != std::string(Output.getFilename()))
+
+  // If we are invoking `nvlink` internally we need to output a `.cubin` file.
+  // Checking if the output is a temporary is the cleanest way to determine
+  // this. Putting this logic in `getInputFIlename` isn't an option because it
+  // relies on the compilation.
+  if (Output.isFilename() &&
+      llvm::find(C.getTempFiles(), Output.getFilename()) !=
+          C.getTempFiles().end()) {
+    SmallString<256> Filename(Output.getFilename());
+    llvm::sys::path::replace_extension(Filename, "cubin");
+    OutputFileName = Args.MakeArgString(Filename);
+  }
+  if (Output.isFilename() && OutputFileName != Output.getFilename())
     C.addTempFile(OutputFileName);
+
   CmdArgs.push_back(OutputFileName);
   for (const auto& II : Inputs)
     CmdArgs.push_back(Args.MakeArgString(II.getFilename()));
 
   for (const auto& A : Args.getAllArgValues(options::OPT_Xcuda_ptxas))
     CmdArgs.push_back(Args.MakeArgString(A));
 
-  bool Relocatable = false;
+  bool Relocatable = true;
   if (JA.isOffloading(Action::OFK_OpenMP))
     // In OpenMP we need to generate relocatable code.
     Relocatable = Args.hasFlag(options::OPT_fopenmp_relocatable_target,
                                options::OPT_fnoopenmp_relocatable_target,
                                /*Default=*/true);
   else if (JA.isOffloading(Action::OFK_Cuda))
+    // In CUDA we generate non-relocatable code by default.
     Relocatable = Args.hasFlag(options::OPT_fgpu_rdc,
                                options::OPT_fno_gpu_rdc, /*Default=*/false);
 
   if (Relocatable)
     CmdArgs.push_back("-c");
 
   const char *Exec;
   if (Arg *A = Args.getLastArg(options::OPT_ptxas_path_EQ))
for (Arg *A : Args) {
     }
   }
   return includePTX;
 }
 
 // All inputs to this linker must be from CudaDeviceActions, as we need to look
 // at the Inputs' Actions in order to figure out which GPU architecture they
 // correspond to.
-void NVPTX::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+void NVPTX::FatBinary::ConstructJob(Compilation &C, const JobAction &JA,
                                     const InputInfo &Output,
                                     const InputInfoList &Inputs,
                                     const ArgList &Args,
                                     const char *LinkingOutput) const {
   const auto &TC =
       static_cast<const toolchains::CudaToolChain &>(getToolChain());
   assert(TC.getTriple().isNVPTX() && "Wrong platform");
 
   ArgStringList CmdArgs;
   if (TC.CudaInstallation.version() <= CudaVersion::CUDA_100)
     CmdArgs.push_back("--cuda");
   CmdArgs.push_back(TC.getTriple().isArch64Bit() ? "-64" : "-32");
void NVPTX::FatBinary::ConstructJob(Compilation &C, const JobAction &JA,
   const char *Exec = Args.MakeArgString(TC.GetProgramPath("fatbinary"));
   C.addCommand(std::make_unique<Command>(
       JA, *this,
       ResponseFileSupport{ResponseFileSupport::RF_Full, llvm::sys::WEM_UTF8,
                           "--options-file"},
       Exec, CmdArgs, Inputs, Output));
 }
 
+void NVPTX::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+                                 const InputInfo &Output,
+                                 const InputInfoList &Inputs,
+                                 const ArgList &Args,
+                                 const char *LinkingOutput) const {
+  const auto &TC =
+      static_cast<const toolchains::NVPTXToolChain &>(getToolChain());
+  assert(TC.getTriple().isNVPTX() && "Wrong platform");
+
+  ArgStringList CmdArgs;
+  if (Output.isFilename()) {
+    CmdArgs.push_back("-o");
+    CmdArgs.push_back(Output.getFilename());
+  } else {
+    assert(Output.isNothing() && "Invalid output.");
+  }
+
+  if (mustEmitDebugInfo(Args) == EmitSameDebugInfoAsHost)
+    CmdArgs.push_back("-g");
+
+  if (Args.hasArg(options::OPT_v))
+    CmdArgs.push_back("-v");
+
+  StringRef GPUArch = Args.getLastArgValue(options::OPT_march_EQ);
+  assert(!GPUArch.empty() && "At least one GPU Arch required for nvlink.");
+
+  CmdArgs.push_back("-arch");
+  CmdArgs.push_back(Args.MakeArgString(GPUArch));
+
+  // Add paths specified in LIBRARY_PATH environment variable as -L options.
+  addDirectoryList(Args, CmdArgs, "-L", "LIBRARY_PATH");
+
+  // Add paths for the default clang library path.
+  SmallString<256> DefaultLibPath =
+      llvm::sys::path::parent_path(TC.getDriver().Dir);
+  llvm::sys::path::append(DefaultLibPath, CLANG_INSTALL_LIBDIR_BASENAME);
+  CmdArgs.push_back(Args.MakeArgString(Twine("-L") + DefaultLibPath));
+
+  for (const auto &II : Inputs) {
+    if (II.getType() == types::TY_LLVM_IR || II.getType() == types::TY_LTO_IR ||
+        II.getType() == types::TY_LTO_BC || II.getType() == types::TY_LLVM_BC) {
+      C.getDriver().Diag(diag::err_drv_no_linker_llvm_support)
+          << getToolChain().getTripleString();
+      continue;
+    }
+
+    // Currently, we only pass the input files to the linker, we do not pass
+    // any libraries that may be valid only for the host.
+    if (!II.isFilename())
+      continue;
+
+    // The 'nvlink' application performs RDC-mode linking when given a '.o'
+    // file and device linking when given a '.cubin' file. We always want to
+    // perform device linking, so just rename any '.o' files.
+    auto InputFile = getToolChain().getInputFilename(II);
+    if (llvm::sys::path::extension(InputFile) != ".cubin") {
+      // If there are no actions above this one then this is direct input and we
+      // can copy it. Otherwise the input is internal so a `.cubin` file should
+      // exist.
+      if (II.getAction() && II.getAction()->getInputs().size() == 0) {
+        const char *CubinF =
+            Args.MakeArgString(getToolChain().getDriver().GetTemporaryPath(
+                llvm::sys::path::stem(InputFile), "cubin"));
+        if (std::error_code EC =
+                llvm::sys::fs::copy_file(InputFile, C.addTempFile(CubinF)))
+          continue;
+
+        CmdArgs.push_back(CubinF);
+      } else {
+        SmallString<256> Filename(InputFile);
+        llvm::sys::path::replace_extension(Filename, "cubin");
+        CmdArgs.push_back(Args.MakeArgString(Filename));
+      }
+    } else {
+      CmdArgs.push_back(Args.MakeArgString(InputFile));
+    }
+  }
+
+  C.addCommand(std::make_unique<Command>(
+      JA, *this,
+      ResponseFileSupport{ResponseFileSupport::RF_Full, llvm::sys::WEM_UTF8,
+                          "--options-file"},
+      Args.MakeArgString(getToolChain().GetProgramPath("nvlink")), CmdArgs,
+      Inputs, Output));
+}
+
 void NVPTX::getNVPTXTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                    const llvm::opt::ArgList &Args,
                                    std::vector<StringRef> &Features) {
   if (Args.hasArg(options::OPT_cuda_feature_EQ)) {
     StringRef PtxFeature =
         Args.getLastArgValue(options::OPT_cuda_feature_EQ, "+ptx42");
     Features.push_back(Args.MakeArgString(PtxFeature));
     return;
case CudaVersion::CUDA_##CUDA_VER:                                           \
     CASE_CUDA_VERSION(90, 60);
 #undef CASE_CUDA_VERSION
   default:
     PtxFeature = "+ptx42";
   }
   Features.push_back(PtxFeature);
 }
 
-/// CUDA toolchain.  Our assembler is ptxas, and our "linker" is fatbinary,
-/// which isn't properly a linker but nonetheless performs the step of stitching
-/// together object files from the assembler into a single blob.
-
-CudaToolChain::CudaToolChain(const Driver &D, const llvm::Triple &Triple,
-                             const ToolChain &HostTC, const ArgList &Args)
-    : ToolChain(D, Triple, Args), HostTC(HostTC),
-      CudaInstallation(D, HostTC.getTriple(), Args) {
+/// NVPTX toolchain. Our assembler is ptxas, and our linker is nvlink. This
+/// operates as a stand-alone version of the NVPTX tools without the host
+/// toolchain.
+NVPTXToolChain::NVPTXToolChain(const Driver &D, const llvm::Triple &Triple,
+                               const llvm::Triple &HostTriple,
+                               const ArgList &Args)
+    : ToolChain(D, Triple, Args), CudaInstallation(D, HostTriple, Args) {
   if (CudaInstallation.isValid()) {
     CudaInstallation.WarnIfUnsupportedVersion();
     getProgramPaths().push_back(std::string(CudaInstallation.getBinPath()));
   }
   // Lookup binaries into the driver directory, this is used to
   // discover the clang-offload-bundler executable.
   getProgramPaths().push_back(getDriver().Dir);
 }
 
-std::string CudaToolChain::getInputFilename(const InputInfo &Input) const {
-  // Only object files are changed, for example assembly files keep their .s
-  // extensions. If the user requested device-only compilation don't change it.
-  if (Input.getType() != types::TY_Object || getDriver().offloadDeviceOnly())
-    return ToolChain::getInputFilename(Input);
+/// We only need the host triple to locate the CUDA binary utilities, use the
+/// system's default triple if not provided.
+NVPTXToolChain::NVPTXToolChain(const Driver &D, const llvm::Triple &Triple,
+                               const ArgList &Args)
+    : NVPTXToolChain(D, Triple,
+                     llvm::Triple(llvm::sys::getDefaultTargetTriple()), Args) {}
 
-  // Replace extension for object files with cubin because nvlink relies on
-  // these particular file names.
-  SmallString<256> Filename(ToolChain::getInputFilename(Input));
-  llvm::sys::path::replace_extension(Filename, "cubin");
-  return std::string(Filename.str());
+llvm::opt::DerivedArgList *
+NVPTXToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
+                              StringRef BoundArch,
+                              Action::OffloadKind DeviceOffloadKind) const {
+  DerivedArgList *DAL =
+      ToolChain::TranslateArgs(Args, BoundArch, DeviceOffloadKind);
+  if (!DAL)
+    DAL = new DerivedArgList(Args.getBaseArgs());
+
+  const OptTable &Opts = getDriver().getOpts();
+
+  for (Arg *A : Args)
+    if (!llvm::is_contained(*DAL, A))
+      DAL->append(A);
+
+  if (!DAL->hasArg(options::OPT_march_EQ))
+    DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_march_EQ),
+                      CudaArchToString(CudaArch::CudaDefault));
+
+  return DAL;
+}
+
+bool NVPTXToolChain::supportsDebugInfoOption(const llvm::opt::Arg *A) const {
+  const Option &O = A->getOption();
+  return (O.matches(options::OPT_gN_Group) &&
+          !O.matches(options::OPT_gmodules)) ||
+         O.matches(options::OPT_g_Flag) ||
+         O.matches(options::OPT_ggdbN_Group) || O.matches(options::OPT_ggdb) ||
+         O.matches(options::OPT_gdwarf) || O.matches(options::OPT_gdwarf_2) ||
+         O.matches(options::OPT_gdwarf_3) || O.matches(options::OPT_gdwarf_4) ||
+         O.matches(options::OPT_gdwarf_5) ||
+         O.matches(options::OPT_gcolumn_info);
+}
+
+void NVPTXToolChain::adjustDebugInfoKind(
+    codegenoptions::DebugInfoKind &DebugInfoKind, const ArgList &Args) const {
+  switch (mustEmitDebugInfo(Args)) {
+  case DisableDebugInfo:
+    DebugInfoKind = codegenoptions::NoDebugInfo;
+    break;
+  case DebugDirectivesOnly:
+    DebugInfoKind = codegenoptions::DebugDirectivesOnly;
+    break;
+  case EmitSameDebugInfoAsHost:
+    // Use same debug info level as the host.
+    break;
+  }
 }
 
+/// CUDA toolchain.  Our assembler is ptxas, and our "linker" is fatbinary,
+/// which isn't properly a linker but nonetheless performs the step of stitching
+/// together object files from the assembler into a single blob.
+
+CudaToolChain::CudaToolChain(const Driver &D, const llvm::Triple &Triple,
+                             const ToolChain &HostTC, const ArgList &Args)
+    : NVPTXToolChain(D, Triple, HostTC.getTriple(), Args), HostTC(HostTC) {}
+
 void CudaToolChain::addClangTargetOptions(
-    const llvm::opt::ArgList &DriverArgs,
-    llvm::opt::ArgStringList &CC1Args,
+    const llvm::opt::ArgList &DriverArgs, llvm::opt::ArgStringList &CC1Args,
     Action::OffloadKind DeviceOffloadingKind) const {
   HostTC.addClangTargetOptions(DriverArgs, CC1Args, DeviceOffloadingKind);
 
   StringRef GpuArch = DriverArgs.getLastArgValue(options::OPT_march_EQ);
   assert(!GpuArch.empty() && "Must have an explicit GPU arch.");
   assert((DeviceOffloadingKind == Action::OFK_OpenMP ||
           DeviceOffloadingKind == Action::OFK_Cuda) &&
          "Only OpenMP or CUDA offloading kinds are supported for NVIDIA GPUs.");
if (FPType && FPType == &llvm::APFloat::IEEEsingle() &&
                            options::OPT_fno_gpu_flush_denormals_to_zero, false))
       return llvm::DenormalMode::getPreserveSign();
   }
 
   assert(JA.getOffloadingDeviceKind() != Action::OFK_Host);
   return llvm::DenormalMode::getIEEE();
 }
 
-bool CudaToolChain::supportsDebugInfoOption(const llvm::opt::Arg *A) const {
-  const Option &O = A->getOption();
-  return (O.matches(options::OPT_gN_Group) &&
-          !O.matches(options::OPT_gmodules)) ||
-         O.matches(options::OPT_g_Flag) ||
-         O.matches(options::OPT_ggdbN_Group) || O.matches(options::OPT_ggdb) ||
-         O.matches(options::OPT_gdwarf) || O.matches(options::OPT_gdwarf_2) ||
-         O.matches(options::OPT_gdwarf_3) || O.matches(options::OPT_gdwarf_4) ||
-         O.matches(options::OPT_gdwarf_5) ||
-         O.matches(options::OPT_gcolumn_info);
-}
-
-void CudaToolChain::adjustDebugInfoKind(
-    codegenoptions::DebugInfoKind &DebugInfoKind, const ArgList &Args) const {
-  switch (mustEmitDebugInfo(Args)) {
-  case DisableDebugInfo:
-    DebugInfoKind = codegenoptions::NoDebugInfo;
-    break;
-  case DebugDirectivesOnly:
-    DebugInfoKind = codegenoptions::DebugDirectivesOnly;
-    break;
-  case EmitSameDebugInfoAsHost:
-    // Use same debug info level as the host.
-    break;
-  }
-}
-
 void CudaToolChain::AddCudaIncludeArgs(const ArgList &DriverArgs,
                                        ArgStringList &CC1Args) const {
   // Check our CUDA version if we're going to include the CUDA headers.
   if (!DriverArgs.hasArg(options::OPT_nogpuinc) &&
       !DriverArgs.hasArg(options::OPT_no_cuda_version_check)) {
     StringRef Arch = DriverArgs.getLastArgValue(options::OPT_march_EQ);
     assert(!Arch.empty() && "Must have an explicit GPU arch.");
     CudaInstallation.CheckCudaVersionSupportsArch(StringToCudaArch(Arch));
   }
   CudaInstallation.AddCudaIncludeArgs(DriverArgs, CC1Args);
 }
 
+std::string CudaToolChain::getInputFilename(const InputInfo &Input) const {
+  // Only object files are changed, for example assembly files keep their .s
+  // extensions. If the user requested device-only compilation don't change it.
+  if (Input.getType() != types::TY_Object || getDriver().offloadDeviceOnly())
+    return ToolChain::getInputFilename(Input);
+
+  // Replace extension for object files with cubin because nvlink relies on
+  // these particular file names.
+  SmallString<256> Filename(ToolChain::getInputFilename(Input));
+  llvm::sys::path::replace_extension(Filename, "cubin");
+  return std::string(Filename.str());
+}
+
 llvm::opt::DerivedArgList *
 CudaToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
                              StringRef BoundArch,
                              Action::OffloadKind DeviceOffloadKind) const {
   DerivedArgList *DAL =
       HostTC.TranslateArgs(Args, BoundArch, DeviceOffloadKind);
   if (!DAL)
     DAL = new DerivedArgList(Args.getBaseArgs());
CudaToolChain::getSystemGPUArchs(const ArgList &Args) const {
 
   if (GPUArchs.empty())
     return llvm::createStringError(std::error_code(),
                                    "No NVIDIA GPU detected in the system");
 
   return std::move(GPUArchs);
 }
 
+Tool *NVPTXToolChain::buildAssembler() const {
+  return new tools::NVPTX::Assembler(*this);
+}
+
+Tool *NVPTXToolChain::buildLinker() const {
+  return new tools::NVPTX::Linker(*this);
+}
+
 Tool *CudaToolChain::buildAssembler() const {
   return new tools::NVPTX::Assembler(*this);
 }
 
 Tool *CudaToolChain::buildLinker() const {
-  return new tools::NVPTX::Linker(*this);
+  return new tools::NVPTX::FatBinary(*this);
 }
 
 void CudaToolChain::addClangWarningOptions(ArgStringList &CC1Args) const {
   HostTC.addClangWarningOptions(CC1Args);
 }
 
 ToolChain::CXXStdlibType
 CudaToolChain::GetCXXStdlibType(const ArgList &Args) const {

clang/test/Driver/cuda-cross-compiling.c

+// Tests the driver when targeting the NVPTX architecture directly without a
+// host toolchain to perform CUDA mappings.
+
+// REQUIRES: nvptx-registered-target
+
+//
+// Test the generated phases when targeting NVPTX.
+//
+// RUN: %clang -target nvptx64-nvidia-cuda -ccc-print-phases %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=PHASES %s
+
+//      PHASES: 0: input, "[[INPUT:.+]]", c
+// PHASES-NEXT: 1: preprocessor, {0}, cpp-output
+// PHASES-NEXT: 2: compiler, {1}, ir
+// PHASES-NEXT: 3: backend, {2}, assembler
+// PHASES-NEXT: 4: assembler, {3}, object
+// PHASES-NEXT: 5: linker, {4}, image
+
+//
+// Test the generated bindings when targeting NVPTX.
+//
+// RUN: %clang -target nvptx64-nvidia-cuda -ccc-print-bindings %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=BINDINGS %s
+
+//      BINDINGS: "nvptx64-nvidia-cuda" - "clang", inputs: ["[[INPUT:.+]]"], output: "[[PTX:.+]].s"
+// BINDINGS-NEXT: "nvptx64-nvidia-cuda" - "NVPTX::Assembler", inputs: ["[[PTX]].s"], output: "[[CUBIN:.+]].o"
+// BINDINGS-NEXT: "nvptx64-nvidia-cuda" - "NVPTX::Linker", inputs: ["[[CUBIN]].o"], output: "a.out"
+
+//
+// Test the generated arguments to the CUDA binary utils when targeting NVPTX. 
+// Ensure that the '.o' files are converted to '.cubin' if produced internally.
+//
+// RUN: %clang -target nvptx64-nvidia-cuda -march=sm_61 -### %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=ARGS %s
+
+//      ARGS: -cc1" "-triple" "nvptx64-nvidia-cuda" "-S" {{.*}} "-target-cpu" "sm_61" "-target-feature" "+ptx{{[0-9]+}}" {{.*}} "-o" "[[PTX:.+]].s"
+// ARGS-NEXT: ptxas" "-m64" "-O0" "--gpu-name" "sm_61" "--output-file" "[[CUBIN:.+]].cubin" "[[PTX]].s" "-c"
+// ARGS-NEXT: nvlink" "-o" "a.out" "-arch" "sm_61" {{.*}} "[[CUBIN]].cubin"
+
+//
+// Test the generated arguments to the CUDA binary utils when targeting NVPTX. 
+// Ensure that we emit '.o' files if compiled with '-c'
+//
+// RUN: %clang -target nvptx64-nvidia-cuda -march=sm_61 -c -### %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=OBJECT %s
+
+//      OBJECT: -cc1" "-triple" "nvptx64-nvidia-cuda" "-S" {{.*}} "-target-cpu" "sm_61" "-target-feature" "+ptx{{[0-9]+}}" {{.*}} "-o" "[[PTX:.+]].s"
+// OBJECT-NEXT: ptxas" "-m64" "-O0" "--gpu-name" "sm_61" "--output-file" "[[OBJ:.+]].o" "[[PTX]].s" "-c"
+
+//
+// Test the generated arguments to the CUDA binary utils when targeting NVPTX. 
+// Ensure that we copy input '.o' files to '.cubin' files when linking.
+//
+// RUN: touch %t.o
+// RUN: %clang -target nvptx64-nvidia-cuda -march=sm_61 -### %t.o 2>&1 \
+// RUN:   | FileCheck -check-prefix=LINK %s
+
+// LINK: nvlink" "-o" "a.out" "-arch" "sm_61" {{.*}} "{{.*}}.cubin"
+
+//
+// Test the generated arguments default to a value with no architecture. 
+//
+// RUN: %clang -target nvptx64-nvidia-cuda -### %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=DEFAULT %s
+
+//      DEFAULT: -cc1" "-triple" "nvptx64-nvidia-cuda" "-S" {{.*}} "-target-cpu" "sm_35" "-target-feature" "+ptx{{[0-9]+}}" {{.*}} "-o" "[[PTX:.+]].s"
+// DEFAULT-NEXT: ptxas" "-m64" "-O0" "--gpu-name" "sm_35" "--output-file" "[[CUBIN:.+]].cubin" "[[PTX]].s" "-c"
+// DEFAULT-NEXT: nvlink" "-o" "a.out" "-arch" "sm_35" {{.*}} "[[CUBIN]].cubin"