[c++2b] Add option -std=c++2b to enable support for potential C++2b features.

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D92547

clang/include/clang/Basic/LangOptions.def

@@ -92,6 +92,7 @@ LANGOPT(CPlusPlus11       , 1, 0, "C++11")
 LANGOPT(CPlusPlus14       , 1, 0, "C++14")
 LANGOPT(CPlusPlus17       , 1, 0, "C++17")
 LANGOPT(CPlusPlus20       , 1, 0, "C++20")
+LANGOPT(CPlusPlus2b       , 1, 0, "C++2b")
 LANGOPT(ObjC              , 1, 0, "Objective-C")
 BENIGN_LANGOPT(ObjCDefaultSynthProperties , 1, 0,
                "Objective-C auto-synthesized properties")

clang/include/clang/Basic/LangStandard.h

@@ -49,11 +49,12 @@ enum LangFeatures {
   CPlusPlus14 = (1 << 7),
   CPlusPlus17 = (1 << 8),
   CPlusPlus20 = (1 << 9),
-  Digraphs = (1 << 10),
-  GNUMode = (1 << 11),
-  HexFloat = (1 << 12),
-  ImplicitInt = (1 << 13),
-  OpenCL = (1 << 14)
+  CPlusPlus2b = (1 << 10),
+  Digraphs = (1 << 11),
+  GNUMode = (1 << 12),
+  HexFloat = (1 << 13),
+  ImplicitInt = (1 << 14),
+  OpenCL = (1 << 15)
 };
 
 /// LangStandard - Information about the properties of a particular language
@@ -111,6 +112,9 @@ public:
   /// isCPlusPlus20 - Language is a C++20 variant (or later).
   bool isCPlusPlus20() const { return Flags & CPlusPlus20; }
 
+  /// isCPlusPlus2b - Language is a post-C++20 variant (or later).
+  bool isCPlusPlus2b() const { return Flags & CPlusPlus2b; }
+
   /// hasDigraphs - Language supports digraphs.
   bool hasDigraphs() const { return Flags & Digraphs; }
 

clang/include/clang/Basic/LangStandards.def

@@ -152,6 +152,16 @@ LANGSTANDARD(gnucxx20, "gnu++20",
              CPlusPlus20 | Digraphs | HexFloat | GNUMode)
 LANGSTANDARD_ALIAS_DEPR(gnucxx20, "gnu++2a")
 
+LANGSTANDARD(cxx2b, "c++2b",
+             CXX, "Working draft for ISO C++ 2023 DIS",
+             LineComment | CPlusPlus | CPlusPlus11 | CPlusPlus14 | CPlusPlus17 |
+             CPlusPlus20 | CPlusPlus2b | Digraphs | HexFloat)
+
+LANGSTANDARD(gnucxx2b, "gnu++2b",
+             CXX, "Working draft for ISO C++ 2023 DIS with GNU extensions",
+             LineComment | CPlusPlus | CPlusPlus11 | CPlusPlus14 | CPlusPlus17 |
+             CPlusPlus20 | CPlusPlus2b | Digraphs | HexFloat | GNUMode)
+
 // OpenCL
 LANGSTANDARD(opencl10, "cl1.0",
              OpenCL, "OpenCL 1.0",

clang/lib/Frontend/CompilerInvocation.cpp

@@ -2388,6 +2388,7 @@ void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
   Opts.CPlusPlus14 = Std.isCPlusPlus14();
   Opts.CPlusPlus17 = Std.isCPlusPlus17();
   Opts.CPlusPlus20 = Std.isCPlusPlus20();
+  Opts.CPlusPlus2b = Std.isCPlusPlus2b();
   Opts.Digraphs = Std.hasDigraphs();
   Opts.GNUMode = Std.isGNUMode();
   Opts.GNUInline = !Opts.C99 && !Opts.CPlusPlus;

clang/lib/Frontend/InitPreprocessor.cpp

@@ -376,8 +376,11 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
       Builder.defineMacro("__STDC_VERSION__", "199409L");
   } else {
     //   -- __cplusplus
+    // FIXME: Use correct value for C++23.
+    if (LangOpts.CPlusPlus2b)
+      Builder.defineMacro("__cplusplus", "202101L");
     //      [C++20] The integer literal 202002L.
-    if (LangOpts.CPlusPlus20)
+    else if (LangOpts.CPlusPlus20)
       Builder.defineMacro("__cplusplus", "202002L");
     //      [C++17] The integer literal 201703L.
     else if (LangOpts.CPlusPlus17)

clang/test/Driver/std.cpp

@@ -11,7 +11,8 @@
 // RUN: not %clang -std=gnu++1z %s -fsyntax-only 2>&1 | FileCheck -check-prefix=GNUXX1Z %s
 // RUN: not %clang -std=c++2a %s -fsyntax-only 2>&1 | FileCheck -check-prefix=CXX2A %s
 // RUN: not %clang -std=gnu++2a %s -fsyntax-only 2>&1 | FileCheck -check-prefix=GNUXX2A %s
-
+// RUN: not %clang -std=c++2b %s -fsyntax-only 2>&1 | FileCheck -check-prefix=CXX2B %s
+// RUN: not %clang -std=gnu++2b %s -fsyntax-only 2>&1 | FileCheck -check-prefix=GNUXX2B %s
 
 void f(int n) {
   typeof(n)();
@@ -48,3 +49,8 @@ void f(int n) {
 // GNUXX2A-NOT: undeclared identifier 'typeof'
 // GNUXX2A-NOT: undeclared identifier 'decltype'
 
+// CXX2B: undeclared identifier 'typeof'
+// CXX2B-NOT: undeclared identifier 'decltype'
+
+// GNUXX2B-NOT: undeclared identifier 'typeof'
+// GNUXX2B-NOT: undeclared identifier 'decltype'

clang/test/Driver/unknown-std.cpp

@@ -17,6 +17,8 @@
 // CHECK-NEXT: note: use 'gnu++17' for 'ISO C++ 2017 with amendments and GNU extensions' standard
 // CHECK-NEXT: note: use 'c++20' for 'ISO C++ 2020 DIS' standard
 // CHECK-NEXT: note: use 'gnu++20' for 'ISO C++ 2020 DIS with GNU extensions' standard
+// CHECK-NEXT: note: use 'c++2b' for 'Working draft for ISO C++ 2023 DIS' standard
+// CHECK-NEXT: note: use 'gnu++2b' for 'Working draft for ISO C++ 2023 DIS with GNU extensions' standard
 // CUDA-NEXT: note: use 'cuda' for 'NVIDIA CUDA(tm)' standard
 
 // Make sure that no other output is present.

clang/test/Preprocessor/init.c

@@ -9,6 +9,15 @@
 // BLOCKS:#define __block __attribute__((__blocks__(byref)))
 //
 //
+// RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=c++2b -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix CXX2B %s
+//
+// CXX2B:#define __GNUG__ 4
+// CXX2B:#define __GXX_EXPERIMENTAL_CXX0X__ 1
+// CXX2B:#define __GXX_RTTI 1
+// CXX2B:#define __GXX_WEAK__ 1
+// CXX2B:#define __cplusplus 202101L
+// CXX2B:#define __private_extern__ extern
+//
 // RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=c++20 -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix CXX2A %s
 // RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=c++2a -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix CXX2A %s
 //
@@ -122,6 +131,13 @@
 // RUN: %clang_cc1 -ffreestanding -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix FREESTANDING %s
 // FREESTANDING:#define __STDC_HOSTED__ 0
 //
+// RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=gnu++2b -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix GXX2B %s
+//
+// GXX2B:#define __GNUG__ 4
+// GXX2B:#define __GXX_WEAK__ 1
+// GXX2B:#define __cplusplus 202101L
+// GXX2B:#define __private_extern__ extern
+//
 // RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=gnu++20 -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix GXX2A %s
 // RUN: %clang_cc1 -x c++ -fgnuc-version=4.2.1 -std=gnu++2a -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix GXX2A %s
 //