[Clang][C++2b] P2242R3: Non-literal variables [...] in constexpr

Allow goto, labelled statements as well as `static`, `thread_local`, and
non-literal variables in `constexpr` functions.

As specified. for all of the above (except labelled statements) constant
evaluation of the construct still fails.

For `constexpr` bodies, the proposal is implemented with diagnostics as
a language extension in older language modes. For determination of
whether a lambda body satisfies the requirements for a constexpr
function, the proposal is implemented only in C++2b mode to retain the
semantics of older modes for programs conforming to them.

Reviewed By: aaron.ballman, hubert.reinterpretcast, erichkeane

Differential Revision: https://reviews.llvm.org/D111400

1 files changed, 5 insertions, 4 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 6b7c743..9d7a429 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -561,10 +561,11 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
     Builder.defineMacro("__cpp_unicode_literals", "200710L");
     Builder.defineMacro("__cpp_user_defined_literals", "200809L");
     Builder.defineMacro("__cpp_lambdas", "200907L");
-    Builder.defineMacro("__cpp_constexpr",
-                        LangOpts.CPlusPlus20 ? "201907L" :
-                        LangOpts.CPlusPlus17 ? "201603L" :
-                        LangOpts.CPlusPlus14 ? "201304L" : "200704");
+    Builder.defineMacro("__cpp_constexpr", LangOpts.CPlusPlus2b   ? "202110L"
+                                           : LangOpts.CPlusPlus20 ? "201907L"
+                                           : LangOpts.CPlusPlus17 ? "201603L"
+                                           : LangOpts.CPlusPlus14 ? "201304L"
+                                                                  : "200704");
     Builder.defineMacro("__cpp_constexpr_in_decltype", "201711L");
     Builder.defineMacro("__cpp_range_based_for",
                         LangOpts.CPlusPlus17 ? "201603L" : "200907");