[flang][OpenMP] Verify that N in -fopenmp-version=N is valid (llvm#145725)

For historical versions that are unsupported, emit a warning and assume
the currently default version.
For values of N that are not integers or that don't correspond to any
OpenMP version (old or newer), emit an error.

Author: kparzysz

flang/lib/Frontend/CompilerInvocation.cpp

@@ -26,6 +26,7 @@
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/OptionUtils.h"
 #include "clang/Driver/Options.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Frontend/Debug/Options.h"
@@ -44,6 +45,7 @@
 #include <cstdlib>
 #include <memory>
 #include <optional>
+#include <sstream>
 
 using namespace Fortran::frontend;
 
@@ -1140,11 +1142,43 @@ static bool parseOpenMPArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
   res.getLangOpts().OpenMPVersion = 31;
   res.getFrontendOpts().features.Enable(
       Fortran::common::LanguageFeature::OpenMP);
-  if (int Version = getLastArgIntValue(
-          args, clang::driver::options::OPT_fopenmp_version_EQ,
-          res.getLangOpts().OpenMPVersion, diags)) {
-    res.getLangOpts().OpenMPVersion = Version;
+  if (auto *arg =
+          args.getLastArg(clang::driver::options::OPT_fopenmp_version_EQ)) {
+    llvm::ArrayRef<unsigned> ompVersions = llvm::omp::getOpenMPVersions();
+    unsigned oldVersions[] = {11, 20, 25, 30};
+    unsigned version = 0;
+
+    auto reportBadVersion = [&](llvm::StringRef value) {
+      const unsigned diagID =
+          diags.getCustomDiagID(clang::DiagnosticsEngine::Error,
+                                "'%0' is not a valid OpenMP version in '%1', "
+                                "valid versions are %2");
+      std::string buffer;
+      llvm::raw_string_ostream versions(buffer);
+      llvm::interleaveComma(ompVersions, versions);
+
+      diags.Report(diagID) << value << arg->getAsString(args) << versions.str();
+    };
+
+    llvm::StringRef value = arg->getValue();
+    if (!value.getAsInteger(/*radix=*/10, version)) {
+      if (llvm::is_contained(ompVersions, version)) {
+        res.getLangOpts().OpenMPVersion = version;
+      } else if (llvm::is_contained(oldVersions, version)) {
+        const unsigned diagID =
+            diags.getCustomDiagID(clang::DiagnosticsEngine::Warning,
+                                  "OpenMP version %0 is no longer supported, "
+                                  "assuming version %1");
+        std::string assumed = std::to_string(res.getLangOpts().OpenMPVersion);
+        diags.Report(diagID) << value << assumed;
+      } else {
+        reportBadVersion(value);
+      }
+    } else {
+      reportBadVersion(value);
+    }
   }
+
   if (args.hasArg(clang::driver::options::OPT_fopenmp_force_usm)) {
     res.getLangOpts().OpenMPForceUSM = 1;
   }

flang/test/Driver/fopenmp-version.F90

@@ -0,0 +1,25 @@
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=31 %s | FileCheck --check-prefix=V31 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=40 %s | FileCheck --check-prefix=V40 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=45 %s | FileCheck --check-prefix=V45 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=50 %s | FileCheck --check-prefix=V50 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=51 %s | FileCheck --check-prefix=V51 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=52 %s | FileCheck --check-prefix=V52 %s
+!RUN: %flang -dM -E -o - -fopenmp -fopenmp-version=60 %s | FileCheck --check-prefix=V60 %s
+
+!V31: #define _OPENMP 201107
+!V40: #define _OPENMP 201307
+!V45: #define _OPENMP 201511
+!V50: #define _OPENMP 201811
+!V51: #define _OPENMP 202011
+!V52: #define _OPENMP 202111
+!V60: #define _OPENMP 202411
+
+
+!RUN: %flang -c -fopenmp -fopenmp-version=25 %s 2>&1 | FileCheck --check-prefix=WARN-ASSUMED %s
+
+!WARN-ASSUMED: warning: OpenMP version 25 is no longer supported, assuming version 31
+
+
+!RUN: not %flang -c -fopenmp -fopenmp-version=29 %s 2>&1 | FileCheck --check-prefix=ERR-BAD %s
+
+!ERR-BAD: error: '29' is not a valid OpenMP version in '-fopenmp-version=29', valid versions are 31, 40, 45, 50, 51, 52, 60