[clang][Basic] Add helper APIs to get language version codes from LangOptions

clang/include/clang/Basic/LangOptions.h

@@ -184,6 +184,28 @@ class LangOptionsBase {
     HLSL_202y = 2029,
   };
 
+  /// C language version codes as defined by the standard.
+  enum CLangStd : uint32_t {
+    // FIXME: Use correct value for C2y.
+    C_2y = 202400,
+    C_23 = 202311,
+    C_17 = 201710,
+    C_11 = 201112,
+    C_99 = 199901,
+  };
+
+  /// C++ language version codes as defined by the standard.
+  enum CPlusPlusLangStd : uint32_t {
+    // FIXME: Use correct value for C++26.
+    CPP_26 = 202400,
+    CPP_23 = 202302,
+    CPP_20 = 202002,
+    CPP_17 = 201703,
+    CPP_14 = 201402,
+    CPP_11 = 201103,
+    CPP_03 = 199711,
+  };
+
   /// Clang versions with different platform ABI conformance.
   enum class ClangABI {
 #define ABI_VER_MAJOR_MINOR(Major, Minor) Ver##Major##_##Minor,
@@ -756,6 +778,15 @@ class LangOptions : public LangOptionsBase {
   bool isTargetDevice() const {
     return OpenMPIsTargetDevice || CUDAIsDevice || SYCLIsDevice;
   }
+
+  /// Returns the most applicable C standard-compliant language version code.
+  /// If none could be determined, returns \ref std::nullopt.
+  std::optional<CLangStd> getCLangStd() const;
+
+  /// Returns the most applicable C++ standard-compliant language
+  /// version code.
+  /// If none could be determined, returns \ref std::nullopt.
+  std::optional<CPlusPlusLangStd> getCPlusPlusLangStd() const;
 };
 
 /// Floating point control options

clang/lib/Basic/LangOptions.cpp

@@ -243,3 +243,49 @@ LLVM_DUMP_METHOD void FPOptionsOverride::dump() {
 #include "clang/Basic/FPOptions.def"
   llvm::errs() << "\n";
 }
+
+std::optional<clang::LangOptionsBase::CPlusPlusLangStd>
+LangOptions::getCPlusPlusLangStd() const {
+  if (!CPlusPlus)
+    return std::nullopt;
+
+  if (CPlusPlus26)
+    return clang::LangOptionsBase::CPP_26;
+
+  if (CPlusPlus23)
+    return clang::LangOptionsBase::CPP_23;
+
+  if (CPlusPlus20)
+    return clang::LangOptionsBase::CPP_20;
+
+  if (CPlusPlus17)
+    return clang::LangOptionsBase::CPP_17;
+
+  if (CPlusPlus14)
+    return clang::LangOptionsBase::CPP_14;
+
+  if (CPlusPlus11)
+    return clang::LangOptionsBase::CPP_11;
+
+  return clang::LangOptionsBase::CPP_03;
+}
+
+std::optional<clang::LangOptionsBase::CLangStd>
+LangOptions::getCLangStd() const {
+  if (C2y)
+    return clang::LangOptionsBase::C_2y;
+
+  if (C23)
+    return clang::LangOptionsBase::C_23;
+
+  if (C17)
+    return clang::LangOptionsBase::C_17;
+
+  if (C11)
+    return clang::LangOptionsBase::C_11;
+
+  if (C99)
+    return clang::LangOptionsBase::C_99;
+
+  return std::nullopt;
+}

clang/lib/Frontend/InitPreprocessor.cpp

@@ -459,43 +459,14 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
   //      value is, are implementation-defined.
   // (Removed in C++20.)
   if (!LangOpts.CPlusPlus) {
-    if (LangOpts.C2y)
-      Builder.defineMacro("__STDC_VERSION__", "202400L");
-    else if (LangOpts.C23)
-      Builder.defineMacro("__STDC_VERSION__", "202311L");
-    else if (LangOpts.C17)
-      Builder.defineMacro("__STDC_VERSION__", "201710L");
-    else if (LangOpts.C11)
-      Builder.defineMacro("__STDC_VERSION__", "201112L");
-    else if (LangOpts.C99)
-      Builder.defineMacro("__STDC_VERSION__", "199901L");
+    if (auto LangStd = LangOpts.getCLangStd())
+      Builder.defineMacro("__STDC_VERSION__", Twine(*LangStd) + "L");
     else if (!LangOpts.GNUMode && LangOpts.Digraphs)
       Builder.defineMacro("__STDC_VERSION__", "199409L");
   } else {
     //   -- __cplusplus
-    if (LangOpts.CPlusPlus26)
-      // FIXME: Use correct value for C++26.
-      Builder.defineMacro("__cplusplus", "202400L");
-    else if (LangOpts.CPlusPlus23)
-      Builder.defineMacro("__cplusplus", "202302L");
-    //      [C++20] The integer literal 202002L.
-    else if (LangOpts.CPlusPlus20)
-      Builder.defineMacro("__cplusplus", "202002L");
-    //      [C++17] The integer literal 201703L.
-    else if (LangOpts.CPlusPlus17)
-      Builder.defineMacro("__cplusplus", "201703L");
-    //      [C++14] The name __cplusplus is defined to the value 201402L when
-    //      compiling a C++ translation unit.
-    else if (LangOpts.CPlusPlus14)
-      Builder.defineMacro("__cplusplus", "201402L");
-    //      [C++11] The name __cplusplus is defined to the value 201103L when
-    //      compiling a C++ translation unit.
-    else if (LangOpts.CPlusPlus11)
-      Builder.defineMacro("__cplusplus", "201103L");
-    //      [C++03] The name __cplusplus is defined to the value 199711L when
-    //      compiling a C++ translation unit.
-    else
-      Builder.defineMacro("__cplusplus", "199711L");
+    Builder.defineMacro("__cplusplus",
+                        Twine(*LangOpts.getCPlusPlusLangStd()) + "L");
 
     //   -- __STDCPP_DEFAULT_NEW_ALIGNMENT__
     //      [C++17] An integer literal of type std::size_t whose value is the

clang/unittests/Basic/CMakeLists.txt

@@ -6,6 +6,7 @@ add_distinct_clang_unittest(BasicTests
   DiagnosticTest.cpp
   FileEntryTest.cpp
   FileManagerTest.cpp
+  LangOptionsTest.cpp
   LineOffsetMappingTest.cpp
   OffloadArchTest.cpp
   SanitizersTest.cpp

clang/unittests/Basic/LangOptionsTest.cpp

@@ -0,0 +1,62 @@
+//===- unittests/Basic/LangOptionsTest.cpp --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/LangOptions.h"
+#include "clang/Testing/CommandLineArgs.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace clang;
+
+namespace {
+TEST(LangOptsTest, CStdLang) {
+  LangOptions opts;
+  EXPECT_FALSE(opts.getCLangStd());
+  opts.C99 = 1;
+  EXPECT_EQ(opts.getCLangStd(), clang::LangOptionsBase::CLangStd::C_99);
+  opts.C11 = 1;
+  EXPECT_EQ(opts.getCLangStd(), clang::LangOptionsBase::CLangStd::C_11);
+  opts.C17 = 1;
+  EXPECT_EQ(opts.getCLangStd(), clang::LangOptionsBase::CLangStd::C_17);
+  opts.C23 = 1;
+  EXPECT_EQ(opts.getCLangStd(), clang::LangOptionsBase::CLangStd::C_23);
+  opts.C2y = 1;
+  EXPECT_EQ(opts.getCLangStd(), clang::LangOptionsBase::CLangStd::C_2y);
+
+  EXPECT_FALSE(opts.getCPlusPlusLangStd());
+}
+
+TEST(LangOptsTest, CppStdLang) {
+  LangOptions opts;
+  EXPECT_FALSE(opts.getCPlusPlusLangStd());
+  opts.CPlusPlus = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_03);
+  opts.CPlusPlus11 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_11);
+  opts.CPlusPlus14 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_14);
+  opts.CPlusPlus17 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_17);
+  opts.CPlusPlus20 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_20);
+  opts.CPlusPlus23 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_23);
+  opts.CPlusPlus26 = 1;
+  EXPECT_EQ(opts.getCPlusPlusLangStd(),
+            clang::LangOptionsBase::CPlusPlusLangStd::CPP_26);
+
+  EXPECT_FALSE(opts.getCLangStd());
+}
+} // namespace