[flang][OpenMP] Remove experimental warning (#144915)

RFC:
https://discourse.llvm.org/t/rfc-removing-the-openmp-experimental-warning-for-llvm-21/86455

Fixes: #110008

Author: tblah

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -143,8 +143,8 @@ def warn_drv_unsupported_option_for_processor : Warning<
 def warn_drv_unsupported_openmp_library : Warning<
   "the library '%0=%1' is not supported, OpenMP will not be enabled">,
   InGroup<OptionIgnored>;
-def warn_openmp_experimental : Warning<
-  "OpenMP support in flang is still experimental">,
+def warn_openmp_incomplete : Warning<
+  "OpenMP support for version %0 in flang is still incomplete">,
   InGroup<ExperimentalOption>;
 
 def err_drv_invalid_thread_model_for_target : Error<

clang/lib/Driver/ToolChains/Flang.cpp

@@ -906,9 +906,6 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
 
       if (Args.hasArg(options::OPT_fopenmp_force_usm))
         CmdArgs.push_back("-fopenmp-force-usm");
-      // TODO: OpenMP support isn't "done" yet, so for now we warn that it
-      // is experimental.
-      D.Diag(diag::warn_openmp_experimental);
 
       // FIXME: Clang supports a whole bunch more flags here.
       break;

flang/lib/Frontend/CompilerInvocation.cpp

@@ -1138,8 +1138,9 @@ static bool parseOpenMPArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
   unsigned numErrorsBefore = diags.getNumErrors();
   llvm::Triple t(res.getTargetOpts().triple);
 
-  // By default OpenMP is set to 3.1 version
-  res.getLangOpts().OpenMPVersion = 31;
+  constexpr unsigned newestFullySupported = 31;
+  // By default OpenMP is set to the most recent fully supported version
+  res.getLangOpts().OpenMPVersion = newestFullySupported;
   res.getFrontendOpts().features.Enable(
       Fortran::common::LanguageFeature::OpenMP);
   if (auto *arg =
@@ -1164,6 +1165,9 @@ static bool parseOpenMPArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
     if (!value.getAsInteger(/*radix=*/10, version)) {
       if (llvm::is_contained(ompVersions, version)) {
         res.getLangOpts().OpenMPVersion = version;
+
+        if (version > newestFullySupported)
+          diags.Report(clang::diag::warn_openmp_incomplete) << version;
       } else if (llvm::is_contained(oldVersions, version)) {
         const unsigned diagID =
             diags.getCustomDiagID(clang::DiagnosticsEngine::Warning,

flang/test/Driver/fopenmp.f90

@@ -74,6 +74,6 @@
 ! CHECK-LD-ANYMD: "{{.*}}ld{{(.exe)?}}"
 ! CHECK-LD-ANYMD: "-l{{(omp|gomp|iomp5md)}}"
 !
-! RUN: %flang -fopenmp -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-EXPERIMENTAL
+! RUN: %flang -fopenmp -fopenmp-version=40 -c %s -S -o - 2>&1 | FileCheck %s --check-prefix=CHECK-INCOMPLETE
 !
-! CHECK-EXPERIMENTAL: flang{{.*}}: warning: OpenMP support in flang is still experimental
+! CHECK-INCOMPLETE: warning: OpenMP support for version 40 in flang is still incomplete