[OpenMP] Improve search for libomptarget-nvptx

When looking for the bclib Clang considered the default library
path first while it preferred directories in LIBRARY_PATH when
constructing the invocation of nvlink. The latter actually makes
more sense because during development it allows using a non-default
runtime library. So change the search for the bclib to start
looking in directories given by LIBRARY_PATH.
Additionally add a new option --libomptarget-nvptx-path= which
will be searched first. This will be handy for testing purposes.

Differential Revision: https://reviews.llvm.org/D51686

llvm-svn: 343230

clang/include/clang/Driver/Options.td

@@ -596,6 +596,8 @@ def hip_device_lib_EQ : Joined<["--"], "hip-device-lib=">, Group<Link_Group>,
   HelpText<"HIP device library">;
 def fhip_dump_offload_linker_script : Flag<["-"], "fhip-dump-offload-linker-script">,
   Group<f_Group>, Flags<[NoArgumentUnused, HelpHidden]>;
+def libomptarget_nvptx_path_EQ : Joined<["--"], "libomptarget-nvptx-path=">, Group<i_Group>,
+  HelpText<"Path to libomptarget-nvptx libraries">;
 def dA : Flag<["-"], "dA">, Group<d_Group>;
 def dD : Flag<["-"], "dD">, Group<d_Group>, Flags<[CC1Option]>,
   HelpText<"Print macro definitions in -E mode in addition to normal output">;

clang/lib/Driver/ToolChains/Cuda.cpp

@@ -511,6 +511,11 @@ void NVPTX::OpenMPLinker::ConstructJob(Compilation &C, const JobAction &JA,
   CmdArgs.push_back("-arch");
   CmdArgs.push_back(Args.MakeArgString(GPUArch));
 
+  // Assume that the directory specified with --libomptarget_nvptx_path
+  // contains the static library libomptarget-nvptx.a.
+  if (const Arg *A = Args.getLastArg(options::OPT_libomptarget_nvptx_path_EQ))
+    CmdArgs.push_back(Args.MakeArgString(Twine("-L") + A->getValue()));
+
   // Add paths specified in LIBRARY_PATH environment variable as -L options.
   addDirectoryList(Args, CmdArgs, "-L", "LIBRARY_PATH");
 
@@ -647,12 +652,9 @@ void CudaToolChain::addClangTargetOptions(
 
   if (DeviceOffloadingKind == Action::OFK_OpenMP) {
     SmallVector<StringRef, 8> LibraryPaths;
-    // Add path to lib and/or lib64 folders.
-    SmallString<256> DefaultLibPath =
-      llvm::sys::path::parent_path(getDriver().Dir);
-    llvm::sys::path::append(DefaultLibPath,
-        Twine("lib") + CLANG_LIBDIR_SUFFIX);
-    LibraryPaths.emplace_back(DefaultLibPath.c_str());
+
+    if (const Arg *A = DriverArgs.getLastArg(options::OPT_libomptarget_nvptx_path_EQ))
+      LibraryPaths.push_back(A->getValue());
 
     // Add user defined library paths from LIBRARY_PATH.
     llvm::Optional<std::string> LibPath =
@@ -665,6 +667,12 @@ void CudaToolChain::addClangTargetOptions(
         LibraryPaths.emplace_back(Path.trim());
     }
 
+    // Add path to lib / lib64 folder.
+    SmallString<256> DefaultLibPath =
+        llvm::sys::path::parent_path(getDriver().Dir);
+    llvm::sys::path::append(DefaultLibPath, Twine("lib") + CLANG_LIBDIR_SUFFIX);
+    LibraryPaths.emplace_back(DefaultLibPath.c_str());
+
     std::string LibOmpTargetName =
       "libomptarget-nvptx-" + GpuArch.str() + ".bc";
     bool FoundBCLibrary = false;

clang/test/Driver/openmp-offload-gpu.c

@@ -30,6 +30,22 @@
 
 /// ###########################################################################
 
+/// Check that -lomptarget-nvptx is passed to nvlink.
+// RUN:   %clang -### -no-canonical-prefixes -fopenmp=libomp \
+// RUN:          -fopenmp-targets=nvptx64-nvidia-cuda %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHK-NVLINK %s
+/// Check that the value of --libomptarget-nvptx-path is forwarded to nvlink.
+// RUN:   %clang -### -no-canonical-prefixes -fopenmp=libomp \
+// RUN:          --libomptarget-nvptx-path=/path/to/libomptarget/ \
+// RUN:          -fopenmp-targets=nvptx64-nvidia-cuda %s 2>&1 \
+// RUN:   | FileCheck -check-prefixes=CHK-NVLINK,CHK-LIBOMPTARGET-NVPTX-PATH %s
+
+// CHK-NVLINK: nvlink
+// CHK-LIBOMPTARGET-NVPTX-PATH-SAME: "-L/path/to/libomptarget/"
+// CHK-NVLINK-SAME: "-lomptarget-nvptx"
+
+/// ###########################################################################
+
 /// Check cubin file generation and usage by nvlink
 // RUN:   %clang -### -no-canonical-prefixes -target powerpc64le-unknown-linux-gnu -fopenmp=libomp \
 // RUN:          -fopenmp-targets=nvptx64-nvidia-cuda -save-temps %s 2>&1 \
@@ -151,6 +167,11 @@
 // RUN:   -Xopenmp-target -march=sm_20 --cuda-path=%S/Inputs/CUDA_80/usr/local/cuda \
 // RUN:   -fopenmp-relocatable-target -save-temps -no-canonical-prefixes %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHK-BCLIB %s
+/// The user can override default detection using --libomptarget-nvptx-path=.
+// RUN:   %clang -### -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda --libomptarget-nvptx-path=%S/Inputs/libomptarget \
+// RUN:   -Xopenmp-target -march=sm_20 --cuda-path=%S/Inputs/CUDA_80/usr/local/cuda \
+// RUN:   -fopenmp-relocatable-target -save-temps -no-canonical-prefixes %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHK-BCLIB %s
 
 // CHK-BCLIB: clang{{.*}}-triple{{.*}}nvptx64-nvidia-cuda{{.*}}-mlink-builtin-bitcode{{.*}}libomptarget-nvptx-sm_20.bc
 // CHK-BCLIB-NOT: {{error:|warning:}}