[HIP] Use nul instead of /dev/null when running on windows

[yaxunl]

Summary

When clang is running on windows, /dev/null is not available. Use nul as empty input file instead.

[rjmccall]

lib/Driver/ToolChains/HIP.cpp

210

How hard would it be to just implement the TODO and get away from a reliance on a null file?

[yaxunl]

lib/Driver/ToolChains/HIP.cpp

210

I tried to make clang-offloader-bundler work without host target but it is not easy. Since it is shared with other languages e.g. OpenMP, it has a fundamental assumption that there is one host target. To make it work without host target may result in format changes that affecting HIP runtime, which is something I would like to avoid for now.

[rjmccall]

lib/Driver/ToolChains/HIP.cpp

210

Okay, if this is the only reasonable way you can find to do it, it's fine.

lib/Driver/ToolChains/HIP.cpp

 #include "llvm/Support/Path.h"
 
 using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace clang::driver::tools;
 using namespace clang;
 using namespace llvm::opt;
 
+#if _WIN32 || _WIN64
+#define NULL_FILE "nul"
+#else
+#define NULL_FILE "/dev/null"
+#endif
+
 namespace {
 
 static void addBCLib(Compilation &C, const ArgList &Args,
                      ArgStringList &CmdArgs, ArgStringList LibraryPaths,
                      StringRef BCName) {
   StringRef FullName;
   for (std::string LibraryPath : LibraryPaths) {
     SmallString<128> Path(LibraryPath);
void AMDGCN::constructHIPFatbinCommand(Compilation &C, const JobAction &JA,
   // Construct clang-offload-bundler command to bundle object files for
   // for different GPU archs.
   ArgStringList BundlerArgs;
   BundlerArgs.push_back(Args.MakeArgString("-type=o"));
 
   // ToDo: Remove the dummy host binary entry which is required by
   // clang-offload-bundler.
   std::string BundlerTargetArg = "-targets=host-x86_64-unknown-linux";
-  std::string BundlerInputArg = "-inputs=/dev/null";
+  std::string BundlerInputArg = "-inputs=" NULL_FILE;
 
   for (const auto &II : Inputs) {
     const auto* A = II.getAction();
     BundlerTargetArg = BundlerTargetArg + ",hip-amdgcn-amd-amdhsa-" +
                        StringRef(A->getOffloadingArch()).str();
     BundlerInputArg = BundlerInputArg + "," + II.getFilename();
   }
   BundlerArgs.push_back(Args.MakeArgString(BundlerTargetArg));