[clang] [llvm] [Clang][C++23] Core language changes from P1467R9 extended floating-point types and standard names. (PR #78503)

[A. Jiang via cfe-commits]

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@@ -470,8 +470,16 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
     if (LangOpts.CPlusPlus26)
       // FIXME: Use correct value for C++26.
       Builder.defineMacro("__cplusplus", "202400L");
-    else if (LangOpts.CPlusPlus23)
+    else if (LangOpts.CPlusPlus23) {
       Builder.defineMacro("__cplusplus", "202302L");
+      // [C++23] 15.11p2 [cpp.predefined]
+      if (TI.hasFloat16Type()) {
+        Builder.defineMacro("__STDCPP_FLOAT16_T__", "1");
+      }
+      if (TI.hasFullBFloat16Type()) {
+        Builder.defineMacro("__STDCPP_BFLOAT16_T__", "1");
+      }
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frederick-vs-ja wrote:

They will get defined in C++26 mode. `LangOpts.CPlusPlus23` means "C++23 and later", not simply "C++23".

Although I think it will make a bit more sense to define these macros in all modes.

https://github.com/llvm/llvm-project/pull/78503