[OpenMP] Add support for linking AMDGPU images

This patch adds support for linking AMDGPU images using the LLD binary.
AMDGPU files are always bitcode images and will always use the LTO
backend. Additionally we now pass the default architecture found with
the `amdgpu-arch` tool to the argument list.

Depends on D117156

Differential Revision: https://reviews.llvm.org/D117246

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

@@ -501,7 +501,7 @@ Expected<std::string> assemble(StringRef InputFile, Triple TheTriple,
   // Create a new file to write the linked device image to.
   SmallString<128> TempFile;
   if (std::error_code EC = sys::fs::createTemporaryFile(
-          TheTriple.getArchName() + "-" + Arch, "cubin", TempFile))
+          "lto-" + TheTriple.getArchName() + "-" + Arch, "cubin", TempFile))
     return createFileError(TempFile, EC);
   TempFiles.push_back(static_cast<std::string>(TempFile));
 
@@ -576,6 +576,50 @@ Expected<std::string> link(ArrayRef<std::string> InputFiles,
   return static_cast<std::string>(TempFile);
 }
 } // namespace nvptx
+namespace amdgcn {
+Expected<std::string> link(ArrayRef<std::string> InputFiles,
+                           ArrayRef<std::string> LinkerArgs, Triple TheTriple,
+                           StringRef Arch) {
+  // AMDGPU uses the lld binary to link device object files.
+  ErrorOr<std::string> LLDPath =
+      sys::findProgramByName("lld", sys::path::parent_path(LinkerExecutable));
+  if (!LLDPath)
+    LLDPath = sys::findProgramByName("lld");
+  if (!LLDPath)
+    return createStringError(LLDPath.getError(),
+                             "Unable to find 'lld' in path");
+
+  // Create a new file to write the linked device image to.
+  SmallString<128> TempFile;
+  if (std::error_code EC = sys::fs::createTemporaryFile(
+          TheTriple.getArchName() + "-" + Arch + "-image", "out", TempFile))
+    return createFileError(TempFile, EC);
+  TempFiles.push_back(static_cast<std::string>(TempFile));
+
+  SmallVector<StringRef, 16> CmdArgs;
+  CmdArgs.push_back(*LLDPath);
+  CmdArgs.push_back("-flavor");
+  CmdArgs.push_back("gnu");
+  CmdArgs.push_back("--no-undefined");
+  CmdArgs.push_back("-shared");
+  CmdArgs.push_back("-o");
+  CmdArgs.push_back(TempFile);
+
+  // Copy system library paths used by the host linker.
+  for (StringRef Arg : LinkerArgs)
+    if (Arg.startswith("-L"))
+      CmdArgs.push_back(Arg);
+
+  // Add extracted input files.
+  for (StringRef Input : InputFiles)
+    CmdArgs.push_back(Input);
+
+  if (sys::ExecuteAndWait(*LLDPath, CmdArgs))
+    return createStringError(inconvertibleErrorCode(), "'lld' failed");
+
+  return static_cast<std::string>(TempFile);
+}
+} // namespace amdgcn
 
 Expected<std::string> linkDevice(ArrayRef<std::string> InputFiles,
                                  ArrayRef<std::string> LinkerArgs,
@@ -585,7 +629,7 @@ Expected<std::string> linkDevice(ArrayRef<std::string> InputFiles,
   case Triple::nvptx64:
     return nvptx::link(InputFiles, LinkerArgs, TheTriple, Arch);
   case Triple::amdgcn:
-    // TODO: AMDGCN linking support.
+    return amdgcn::link(InputFiles, LinkerArgs, TheTriple, Arch);
   case Triple::x86:
   case Triple::x86_64:
     // TODO: x86 linking support.