[clang] [flang] [FLANG] allow -fopenmp= (PR #86816)

[Mats Petersson via cfe-commits]

================
@@ -764,6 +762,32 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
   // Add other compile options
   addOtherOptions(Args, CmdArgs);
 
+  // Forward flags for OpenMP. We don't do this if the current action is an
+  // device offloading action other than OpenMP.
+  if (Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
+                   options::OPT_fno_openmp, false) &&
+      (JA.isDeviceOffloading(Action::OFK_None) ||
+       JA.isDeviceOffloading(Action::OFK_OpenMP))) {
+    switch (D.getOpenMPRuntime(Args)) {
+    case Driver::OMPRT_OMP:
+    case Driver::OMPRT_IOMP5:
+      // Clang can generate useful OpenMP code for these two runtime libraries.
+      CmdArgs.push_back("-fopenmp");
+      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_version_EQ);
+
+      // FIXME: Clang supports a whole bunch more flags here.
----------------
Leporacanthicus wrote:

Roughly this bunch.

```      // If no option regarding the use of TLS in OpenMP codegeneration is
      // given, decide a default based on the target. Otherwise rely on the
      // options and pass the right information to the frontend.
      if (!Args.hasFlag(options::OPT_fopenmp_use_tls,
                        options::OPT_fnoopenmp_use_tls, /*Default=*/true))
        CmdArgs.push_back("-fnoopenmp-use-tls");
      Args.AddLastArg(CmdArgs, options::OPT_fopenmp_simd,
                      options::OPT_fno_openmp_simd);
      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_enable_irbuilder);
      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_version_EQ);
      if (!Args.hasFlag(options::OPT_fopenmp_extensions,
                        options::OPT_fno_openmp_extensions, /*Default=*/true))
        CmdArgs.push_back("-fno-openmp-extensions");
      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_cuda_number_of_sm_EQ);
      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_cuda_blocks_per_sm_EQ);
      Args.AddAllArgs(CmdArgs,
                      options::OPT_fopenmp_cuda_teams_reduction_recs_num_EQ);
      if (Args.hasFlag(options::OPT_fopenmp_optimistic_collapse,
                       options::OPT_fno_openmp_optimistic_collapse,
                       /*Default=*/false))
        CmdArgs.push_back("-fopenmp-optimistic-collapse");

      // When in OpenMP offloading mode with NVPTX target, forward
      // cuda-mode flag
      if (Args.hasFlag(options::OPT_fopenmp_cuda_mode,
                       options::OPT_fno_openmp_cuda_mode, /*Default=*/false))
        CmdArgs.push_back("-fopenmp-cuda-mode");

      // When in OpenMP offloading mode, enable debugging on the device.
      Args.AddAllArgs(CmdArgs, options::OPT_fopenmp_target_debug_EQ);
      if (Args.hasFlag(options::OPT_fopenmp_target_debug,
                       options::OPT_fno_openmp_target_debug, /*Default=*/false))
        CmdArgs.push_back("-fopenmp-target-debug");

      // When in OpenMP offloading mode, forward assumptions information about
      // thread and team counts in the device.
      if (Args.hasFlag(options::OPT_fopenmp_assume_teams_oversubscription,
                       options::OPT_fno_openmp_assume_teams_oversubscription,
                       /*Default=*/false))
        CmdArgs.push_back("-fopenmp-assume-teams-oversubscription");
      if (Args.hasFlag(options::OPT_fopenmp_assume_threads_oversubscription,
                       options::OPT_fno_openmp_assume_threads_oversubscription,
                       /*Default=*/false))
        CmdArgs.push_back("-fopenmp-assume-threads-oversubscription");
      if (Args.hasArg(options::OPT_fopenmp_assume_no_thread_state))
        CmdArgs.push_back("-fopenmp-assume-no-thread-state");
      if (Args.hasArg(options::OPT_fopenmp_assume_no_nested_parallelism))
        CmdArgs.push_back("-fopenmp-assume-no-nested-parallelism");
      if (Args.hasArg(options::OPT_fopenmp_offload_mandatory))
        CmdArgs.push_back("-fopenmp-offload-mandatory");
      if (Args.hasArg(options::OPT_fopenmp_force_usm))
        CmdArgs.push_back("-fopenmp-force-usm");
```



https://github.com/llvm/llvm-project/pull/86816