[OpenMP] Add support for CPU offloading in new driver

[jhuber6]

Summary

This patch adds support for linking CPU offloading applications in the
linker wrapper. We generate the necessary linking job using the host
linker's path and library arguments. This may not be true for more
complex offloading schemes, but this is sufficient for now.

[jhuber6]

Fixing LTO.

[jdoerfert]

We should be able to test this with unit tests, no?

[jhuber6]

Add test for the arguments passed to the linker wrapper when doing host
offloading. It will be more difficult to do a unit test for the internal
operation of the linker wrapper because it is reactive to the data contained in
the object file.

[jdoerfert]

LG

clang/lib/Driver/ToolChains/Clang.cpp

if (D.isUsingLTO(/* IsOffload */ true)) {
     // Pass in target features for each toolchain.
     for (auto &I :
          llvm::make_range(OpenMPTCRange.first, OpenMPTCRange.second)) {
       const ToolChain *TC = I.second;
       const ArgList &TCArgs = C.getArgsForToolChain(TC, "", Action::OFK_OpenMP);
       ArgStringList FeatureArgs;
       TC->addClangTargetOptions(TCArgs, FeatureArgs, Action::OFK_OpenMP);
       auto FeatureIt = llvm::find(FeatureArgs, "-target-feature");
-      CmdArgs.push_back(Args.MakeArgString(
-          "-target-feature=" + TC->getTripleString() + "=" + *(FeatureIt + 1)));
+      if (FeatureIt != FeatureArgs.end())
+        CmdArgs.push_back(
+            Args.MakeArgString("-target-feature=" + TC->getTripleString() +
+                               "=" + *(FeatureIt + 1)));
     }
 
     // Pass in the bitcode library to be linked during LTO.
     for (auto &I :
          llvm::make_range(OpenMPTCRange.first, OpenMPTCRange.second)) {
       const ToolChain *TC = I.second;
+      if (!(TC->getTriple().isNVPTX() || TC->getTriple().isAMDGPU()))
+        continue;
+
       const Driver &TCDriver = TC->getDriver();
       const ArgList &TCArgs = C.getArgsForToolChain(TC, "", Action::OFK_OpenMP);
       StringRef Arch = TCArgs.getLastArgValue(options::OPT_march_EQ);
 
       ArgStringList BitcodeLibrary;
       addOpenMPDeviceRTL(TCDriver, TCArgs, BitcodeLibrary, Arch,
                          TC->getTriple());
 

clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp

Expected<std::string> link(ArrayRef<std::string> InputFiles, Triple TheTriple,
 
   if (sys::ExecuteAndWait(*LLDPath, CmdArgs))
     return createStringError(inconvertibleErrorCode(), "'lld' failed");
 
   return static_cast<std::string>(TempFile);
 }
 } // namespace amdgcn
 
+namespace generic {
+
+const char *getLDMOption(const llvm::Triple &T) {
+  switch (T.getArch()) {
+  case llvm::Triple::x86:
+    if (T.isOSIAMCU())
+      return "elf_iamcu";
+    return "elf_i386";
+  case llvm::Triple::aarch64:
+    return "aarch64linux";
+  case llvm::Triple::aarch64_be:
+    return "aarch64linuxb";
+  case llvm::Triple::ppc64:
+    return "elf64ppc";
+  case llvm::Triple::ppc64le:
+    return "elf64lppc";
+  case llvm::Triple::x86_64:
+    if (T.isX32())
+      return "elf32_x86_64";
+    return "elf_x86_64";
+  case llvm::Triple::ve:
+    return "elf64ve";
+  default:
+    return nullptr;
+  }
+}
+
+Expected<std::string> link(ArrayRef<std::string> InputFiles, Triple TheTriple,
+                           StringRef Arch) {
+  // Create a new file to write the linked device image to.
+  SmallString<128> TempFile;
+  if (Error Err = createOutputFile(sys::path::filename(ExecutableName) + "-" +
+                                       TheTriple.getArchName() + "-" + Arch,
+                                   "out", TempFile))
+    return std::move(Err);
+
+  // Use the host linker to perform generic offloading. Use the same libraries
+  // and paths as the host application does.
+  SmallVector<StringRef, 16> CmdArgs;
+  CmdArgs.push_back(LinkerUserPath);
+  CmdArgs.push_back("-m");
+  CmdArgs.push_back(getLDMOption(TheTriple));
+  CmdArgs.push_back("-shared");
+  for (auto AI = HostLinkerArgs.begin(), AE = HostLinkerArgs.end(); AI != AE;
+       ++AI) {
+    StringRef Arg = *AI;
+    if (Arg.startswith("-L"))
+      CmdArgs.push_back(Arg);
+    else if (Arg.startswith("-l"))
+      CmdArgs.push_back(Arg);
+    else if (Arg.startswith("--as-needed"))
+      CmdArgs.push_back(Arg);
+    else if (Arg.startswith("--no-as-needed"))
+      CmdArgs.push_back(Arg);
+    else if (Arg.startswith("-rpath")) {
+      CmdArgs.push_back(Arg);
+      CmdArgs.push_back(*(AI + 1));
+    } else if (Arg.startswith("-dynamic-linker")) {
+      CmdArgs.push_back(Arg);
+      CmdArgs.push_back(*(AI + 1));
+    }
+  }
+  CmdArgs.push_back("-Bsymbolic");
+  CmdArgs.push_back("-o");
+  CmdArgs.push_back(TempFile);
+
+  // Add extracted input files.
+  for (StringRef Input : InputFiles)
+    CmdArgs.push_back(Input);
+
+  if (sys::ExecuteAndWait(LinkerUserPath, CmdArgs))
+    return createStringError(inconvertibleErrorCode(), "'linker' failed");
+
+  return static_cast<std::string>(TempFile);
+}
+} // namespace generic
+
 Expected<std::string> linkDevice(ArrayRef<std::string> InputFiles,
                                  Triple TheTriple, StringRef Arch) {
   switch (TheTriple.getArch()) {
   case Triple::nvptx:
   case Triple::nvptx64:
     return nvptx::link(InputFiles, TheTriple, Arch);
   case Triple::amdgcn:
     return amdgcn::link(InputFiles, TheTriple, Arch);
   case Triple::x86:
   case Triple::x86_64:
-    // TODO: x86 linking support.
+  case Triple::aarch64:
+  case Triple::aarch64_be:
+  case Triple::ppc64:
+  case Triple::ppc64le:
+    return generic::link(InputFiles, TheTriple, Arch);
   default:
     return createStringError(inconvertibleErrorCode(),
                              TheTriple.getArchName() +
                                  " linking is not supported");
   }
 }
 
 void diagnosticHandler(const DiagnosticInfo &DI) {