[flang][Driver] support -fno-openmp (#107087)

Closes #83148

Author: tblah

clang/include/clang/Driver/Options.td

@@ -3545,6 +3545,7 @@ def fopenmp : Flag<["-"], "fopenmp">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
   HelpText<"Parse OpenMP pragmas and generate parallel code.">;
 def fno_openmp : Flag<["-"], "fno-openmp">, Group<f_Group>,
+  Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
   Flags<[NoArgumentUnused]>;
 class OpenMPVersionHelp<string program, string default> {
   string str = !strconcat(

flang/lib/Frontend/CompilerInvocation.cpp

@@ -968,7 +968,9 @@ static bool parseDialectArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
 /// generated.
 static bool parseOpenMPArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
                             clang::DiagnosticsEngine &diags) {
-  if (!args.hasArg(clang::driver::options::OPT_fopenmp))
+  llvm::opt::Arg *arg = args.getLastArg(clang::driver::options::OPT_fopenmp,
+                                        clang::driver::options::OPT_fno_openmp);
+  if (!arg || arg->getOption().matches(clang::driver::options::OPT_fno_openmp))
     return true;
 
   unsigned numErrorsBefore = diags.getNumErrors();

flang/test/Driver/fno-openmp.f90

@@ -0,0 +1,12 @@
+! RUN: %flang_fc1 -fopenmp -fno-openmp %s -emit-hlfir -o - | FileCheck --check-prefix=CHECK-NO-OMP %s
+! RUN: %flang_fc1 -fno-openmp %s -emit-hlfir -o - | FileCheck --check-prefix=CHECK-NO-OMP %s
+! RUN: %flang_fc1 -fno-openmp -fopenmp %s -emit-hlfir -o - | FileCheck --check-prefix=CHECK-OMP %s
+! RUN: %flang_fc1 -fopenmp %s -emit-hlfir -o - | FileCheck --check-prefix=CHECK-OMP %s
+
+subroutine main
+  ! CHECK-NO-OMP-NOT: omp.parallel
+  ! CHECK-OMP: omp.parallel
+  !$omp parallel
+  print *,"test"
+  !$omp end parallel
+end subroutine

flang/test/Driver/fopenmp.f90

@@ -11,6 +11,9 @@
 ! RUN: %flang -target x86_64-windows-gnu -fopenmp=libgomp -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FC1-NO-OPENMP --check-prefix=CHECK-WARNING
 ! RUN: %flang -target x86_64-windows-gnu -fopenmp=libiomp5 -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FC1-OPENMP
 
+!RUN: %flang -fno-openmp -fopenmp -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FC1-OPENMP
+!RUN: %flang -fopenmp -fno-openmp -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FC1-NO-OPENMP
+
 ! CHECK-FC1-OPENMP: "-fc1"
 ! CHECK-FC1-OPENMP: "-fopenmp"
 !
@@ -59,8 +62,14 @@
 ! RUN: %flang -target x86_64-freebsd -fopenmp %s -o %t -### 2>&1 | FileCheck %s --check-prefix=CHECK-LD-ANY
 ! RUN: %flang -target x86_64-windows-gnu -fopenmp %s -o %t -### 2>&1 | FileCheck %s --check-prefix=CHECK-LD-ANYMD
 !
+! RUN: %flang -target x86_64-linux-gnu -fno-openmp -fopenmp %s -o %t -### 2>&1 | FileCheck %s --check-prefix=CHECK-LD-ANY
+! RUN: %flang -target x86_64-linux-gnu -fopenmp -fno-openmp %s -o %t -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-LD-ANY
+!
 ! CHECK-LD-ANY: "{{.*}}ld{{(.exe)?}}"
 ! CHECK-LD-ANY: "-l{{(omp|gomp|iomp5)}}"
 !
+! CHECK-NO-LD-ANY:     "{{.*}}ld{{(.exe)?}}"
+! CHECK-NO-LD-ANY-NOT: "-l{{(omp|gomp|iomp5)}}"
+!
 ! CHECK-LD-ANYMD: "{{.*}}ld{{(.exe)?}}"
 ! CHECK-LD-ANYMD: "-l{{(omp|gomp|iomp5md)}}"