[c++20] P1143R2: Add support for the C++20 'constinit' keyword.

This is mostly the same as the
[[clang::require_constant_initialization]] attribute, but has a couple
of additional syntactic and semantic restrictions.

In passing, I added a warning for the attribute form being added after
we have already seen the initialization of the variable (but before we
see the definition); that case previously slipped between the cracks and
the attribute was silently ignored.

llvm-svn: 370972

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 6eafe81e826..95d9f62c608 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -541,8 +541,10 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
     Builder.defineMacro("__cpp_template_template_args", "201611L");
 
   // C++20 features.
-  if (LangOpts.CPlusPlus2a)
+  if (LangOpts.CPlusPlus2a) {
     Builder.defineMacro("__cpp_conditional_explicit", "201806L");
+    Builder.defineMacro("__cpp_constinit", "201907L");
+  }
   if (LangOpts.Char8)
     Builder.defineMacro("__cpp_char8_t", "201811L");
   Builder.defineMacro("__cpp_impl_destroying_delete", "201806L");