[openmp] Accept directory for libomptarget-bc-path

The commandline flag to specify a particular openmp devicertl library
currently errors like:
```
fatal error: cannot open file
      './runtimes/runtimes-bins/openmp/libomptarget':
      Is a directory
```
CommonArgs successfully appends the directory to the commandline args then
mlink-builtin-bitcode rejects it.

This patch is a point fix to that. If --libomptarget-amdgcn-bc-path=directory
then append the expected name for the current architecture and go on as before.
This is useful for test runners that don't hardcode the architecture.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D109057

Author: JonChesterfield

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1709,22 +1709,26 @@ void tools::addOpenMPDeviceRTL(const Driver &D,
                         : options::OPT_libomptarget_nvptx_bc_path_EQ;
 
   StringRef ArchPrefix = Triple.isAMDGCN() ? "amdgcn" : "nvptx";
+  std::string LibOmpTargetName = "libomptarget-" + BitcodeSuffix.str() + ".bc";
+
   // First check whether user specifies bc library
   if (const Arg *A = DriverArgs.getLastArg(LibomptargetBCPathOpt)) {
-    std::string LibOmpTargetName(A->getValue());
-    if (llvm::sys::fs::exists(LibOmpTargetName)) {
+    SmallString<128> LibOmpTargetFile(A->getValue());
+    if (llvm::sys::fs::exists(LibOmpTargetFile) &&
+        llvm::sys::fs::is_directory(LibOmpTargetFile)) {
+      llvm::sys::path::append(LibOmpTargetFile, LibOmpTargetName);
+    }
+
+    if (llvm::sys::fs::exists(LibOmpTargetFile)) {
       CC1Args.push_back("-mlink-builtin-bitcode");
-      CC1Args.push_back(DriverArgs.MakeArgString(LibOmpTargetName));
+      CC1Args.push_back(DriverArgs.MakeArgString(LibOmpTargetFile));
     } else {
       D.Diag(diag::err_drv_omp_offload_target_bcruntime_not_found)
-          << LibOmpTargetName;
+          << LibOmpTargetFile;
     }
   } else {
     bool FoundBCLibrary = false;
 
-    std::string LibOmpTargetName =
-        "libomptarget-" + BitcodeSuffix.str() + ".bc";
-
     for (StringRef LibraryPath : LibraryPaths) {
       SmallString<128> LibOmpTargetFile(LibraryPath);
       llvm::sys::path::append(LibOmpTargetFile, LibOmpTargetName);

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

@@ -165,11 +165,17 @@
 // RUN:   -Xopenmp-target -march=sm_35 --cuda-path=%S/Inputs/CUDA_102/usr/local/cuda \
 // RUN:   -fopenmp-relocatable-target -save-temps -no-canonical-prefixes %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHK-BCLIB-USER %s
+/// The user can also pass the path to the directory containing the bitcode lib
+// RUN:   %clang -### -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda \
+// RUN:   --libomptarget-nvptx-bc-path=%S/Inputs/libomptarget \
+// RUN:   -Xopenmp-target -march=sm_35 --cuda-path=%S/Inputs/CUDA_102/usr/local/cuda \
+// RUN:   -fopenmp-relocatable-target -save-temps -no-canonical-prefixes %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHK-BCLIB-USER-DIR %s
 
 // CHK-BCLIB: clang{{.*}}-triple{{.*}}nvptx64-nvidia-cuda{{.*}}-mlink-builtin-bitcode{{.*}}libomptarget-nvptx-sm_35.bc
 // CHK-BCLIB-NEW: clang{{.*}}-triple{{.*}}nvptx64-nvidia-cuda{{.*}}-mlink-builtin-bitcode{{.*}}libomptarget-new-nvptx-sm_35.bc
 // CHK-BCLIB-USER: clang{{.*}}-triple{{.*}}nvptx64-nvidia-cuda{{.*}}-mlink-builtin-bitcode{{.*}}libomptarget-nvptx-test.bc
-
+// CHK-BCLIB-USER-DIR: clang{{.*}}-triple{{.*}}nvptx64-nvidia-cuda{{.*}}-mlink-builtin-bitcode{{.*}}libomptarget{{.}}libomptarget-nvptx-sm_35.bc
 // CHK-BCLIB-NOT: {{error:|warning:}}
 
 /// ###########################################################################