[c++2a] Add option -std=c++2a to enable support for potential/transitional C++2a features

- as usual C++2a implies all the C++'s that came before it.

Thank you Aaron for the feedback here: https://reviews.llvm.org/D35454 

llvm-svn: 308118

2 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 00f6b9b46f0..b2c14554a4b 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1683,6 +1683,7 @@ void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
   Opts.CPlusPlus11 = Std.isCPlusPlus11();
   Opts.CPlusPlus14 = Std.isCPlusPlus14();
   Opts.CPlusPlus1z = Std.isCPlusPlus1z();
+  Opts.CPlusPlus2a = Std.isCPlusPlus2a();
   Opts.Digraphs = Std.hasDigraphs();
   Opts.GNUMode = Std.isGNUMode();
   Opts.GNUInline = !Opts.C99 && !Opts.CPlusPlus;
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 71420df0002..64128dfdf53 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -374,10 +374,13 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
     else if (!LangOpts.GNUMode && LangOpts.Digraphs)
       Builder.defineMacro("__STDC_VERSION__", "199409L");
   } else {
+    // FIXME: Use correct value for C++20.
+    if (LangOpts.CPlusPlus2a)
+      Builder.defineMacro("__cplusplus", "201707L");
     // C++17 [cpp.predefined]p1:
     //   The name __cplusplus is defined to the value 201703L when compiling a
     //   C++ translation unit.
-    if (LangOpts.CPlusPlus1z)
+    else if (LangOpts.CPlusPlus1z)
       Builder.defineMacro("__cplusplus", "201703L");
     // C++1y [cpp.predefined]p1:
     //   The name __cplusplus is defined to the value 201402L when compiling a