[flang][cuda] Enable cuda with -x cuda option (llvm#84944)

Flang driver was already able to enable the CUDA language feature base
on the file extension but there was no command line option. This PR adds
one.

Author: clementval

flang/lib/Frontend/CompilerInvocation.cpp

@@ -581,6 +581,8 @@ static bool parseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
                 // pre-processed inputs.
                 .Case("f95", Language::Fortran)
                 .Case("f95-cpp-input", Language::Fortran)
+                // CUDA Fortran
+                .Case("cuda", Language::Fortran)
                 .Default(Language::Unknown);
 
     // Flang's intermediate representations.
@@ -877,6 +879,13 @@ static bool parseDialectArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
   if (args.hasArg(clang::driver::options::OPT_flarge_sizes))
     res.getDefaultKinds().set_sizeIntegerKind(8);
 
+  // -x cuda
+  auto language = args.getLastArgValue(clang::driver::options::OPT_x);
+  if (language.equals("cuda")) {
+    res.getFrontendOpts().features.Enable(
+        Fortran::common::LanguageFeature::CUDA);
+  }
+
   // -fopenmp and -fopenacc
   if (args.hasArg(clang::driver::options::OPT_fopenacc)) {
     res.getFrontendOpts().features.Enable(

flang/lib/Frontend/FrontendAction.cpp

@@ -86,9 +86,14 @@ bool FrontendAction::beginSourceFile(CompilerInstance &ci,
     invoc.collectMacroDefinitions();
   }
 
-  // Enable CUDA Fortran if source file is *.cuf/*.CUF.
-  invoc.getFortranOpts().features.Enable(Fortran::common::LanguageFeature::CUDA,
-                                         getCurrentInput().getIsCUDAFortran());
+  if (!invoc.getFortranOpts().features.IsEnabled(
+          Fortran::common::LanguageFeature::CUDA)) {
+    // Enable CUDA Fortran if source file is *.cuf/*.CUF and not already
+    // enabled.
+    invoc.getFortranOpts().features.Enable(
+        Fortran::common::LanguageFeature::CUDA,
+        getCurrentInput().getIsCUDAFortran());
+  }
 
   // Decide between fixed and free form (if the user didn't express any
   // preference, use the file extension to decide)

flang/test/Driver/cuda-option.f90

@@ -0,0 +1,15 @@
+! Test -fcuda option
+! RUN: %flang -fc1 -cpp -x cuda -fdebug-unparse %s -o - | FileCheck %s
+! RUN: not %flang -fc1 -cpp %s -o - 2>&1 | FileCheck %s --check-prefix=ERROR
+program main
+#if _CUDA
+  integer :: var = _CUDA
+#endif
+  integer, device :: dvar
+end program
+
+! CHECK-LABEL: PROGRAM main
+! CHECK: INTEGER :: var = 1
+! CHECK: INTEGER, DEVICE :: dvar
+
+! ERROR: cuda-option.f90:8:19: error: expected end of statement