[AMDGPU] Support -mcpu=native for OpenCL

When -mcpu=native is specified, try detecting GPU
on the system by using amdgpu-arch tool. If it
fails to detect GPU, emit an error about GPU
not detected. If multiple GPUs are detected,
use the first GPU and emit a warning.

Reviewed by: Matt Arsenault, Fangrui Song

Differential Revision: https://reviews.llvm.org/D154531

Author: yxsamliu

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -82,6 +82,9 @@ def err_drv_hipspv_no_hip_path : Error<
 def err_drv_undetermined_gpu_arch : Error<
   "cannot determine %0 architecture: %1; consider passing it via "
   "'%2'">;
+def warn_drv_multi_gpu_arch : Warning<
+  "multiple %0 architectures are detected: %1; only the first one is used for "
+  "'%2'">, InGroup<MultiGPU>;
 def err_drv_cuda_version_unsupported : Error<
   "GPU arch %0 is supported by CUDA versions between %1 and %2 (inclusive), "
   "but installation at %3 is %4; use '--cuda-path' to specify a different CUDA "

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1336,6 +1336,9 @@ def HIPOnly : DiagGroup<"hip-only">;
 // Warning about mixed HIP and OpenMP compilation / target offloading.
 def HIPOpenMPOffloading: DiagGroup<"hip-omp-target-directives">;
 
+// Warning about multiple GPUs are detected.
+def MultiGPU: DiagGroup<"multi-gpu">;
+
 // Warnings which cause linking of the runtime libraries like
 // libc and the CRT to be skipped.
 def AVRRtlibLinkingQuirks : DiagGroup<"avr-rtlib-linking-quirks">;

clang/lib/Driver/ToolChains/AMDGPU.cpp

@@ -635,6 +635,27 @@ AMDGPUToolChain::TranslateArgs(const DerivedArgList &Args, StringRef BoundArch,
   for (Arg *A : Args)
     DAL->append(A);
 
+  // Replace -mcpu=native with detected GPU.
+  Arg *LastMCPUArg = DAL->getLastArg(options::OPT_mcpu_EQ);
+  if (LastMCPUArg && StringRef(LastMCPUArg->getValue()) == "native") {
+    DAL->eraseArg(options::OPT_mcpu_EQ);
+    auto GPUsOrErr = getSystemGPUArchs(Args);
+    if (!GPUsOrErr) {
+      getDriver().Diag(diag::err_drv_undetermined_gpu_arch)
+          << llvm::Triple::getArchTypeName(getArch())
+          << llvm::toString(GPUsOrErr.takeError()) << "-mcpu";
+    } else {
+      auto &GPUs = *GPUsOrErr;
+      if (GPUs.size() > 1) {
+        getDriver().Diag(diag::warn_drv_multi_gpu_arch)
+            << llvm::Triple::getArchTypeName(getArch())
+            << llvm::join(GPUs, ", ") << "-mcpu";
+      }
+      DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_mcpu_EQ),
+                        Args.MakeArgString(GPUs.front()));
+    }
+  }
+
   checkTargetID(*DAL);
 
   if (!Args.getLastArgValue(options::OPT_x).equals("cl"))