Add support for -std=c++2a.

	* c-common.h (cxx_dialect): Add cxx2a as a dialect.
	* opt.c: Add options for -std=c++2a and -std=gnu++2a.
	* c-opts.c (set_std_cxx2a): New.
	(c_common_handle_option): Set options when -std=c++2a is enabled.
	(c_common_post_options): Adjust comments.
	(set_std_cxx14, set_std_cxx17): Likewise.

	* doc/cpp.texi (__cplusplus): Document value for -std=c++2a
	or -std=gnu+2a.
	* doc/invoke.texi: Document -std=c++2a and -std=gnu++2a.

	* lib/target-supports.exp (check_effective_target_c++17): Return
	1 also if check_effective_target_c++2a.
	(check_effective_target_c++17_down): New.
	(check_effective_target_c++2a_only): New.
	(check_effective_target_c++2a): New.
	* g++.dg/cpp2a/cplusplus.C: New.

	* include/cpplib.h (c_lang): Add CXX2A and GNUCXX2A.
	* init.c (lang_defaults): Add rows for CXX2A and GNUCXX2A.
	(cpp_init_builtins): Set __cplusplus to 201709L for C++2a.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r252850

10 files changed, 113 insertions, 6 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6535022..1b5176a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2017-09-15  Andrew Sutton  <andrew.n.sutton@gmail.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	Add support for -std=c++2a.
+	* doc/cpp.texi (__cplusplus): Document value for -std=c++2a
+	or -std=gnu+2a.
+	* doc/invoke.texi: Document -std=c++2a and -std=gnu++2a.
+
 2017-09-15  Steve Ellcey  <sellcey@cavium.com>
 
 	PR target/82066
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index a3f990d..8003fb5 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,14 @@
+2017-09-15  Andrew Sutton  <andrew.n.sutton@gmail.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	Add support for -std=c++2a.
+	* c-common.h (cxx_dialect): Add cxx2a as a dialect.
+	* opt.c: Add options for -std=c++2a and -std=gnu++2a.
+	* c-opts.c (set_std_cxx2a): New.
+	(c_common_handle_option): Set options when -std=c++2a is enabled.
+	(c_common_post_options): Adjust comments.
+	(set_std_cxx14, set_std_cxx17): Likewise.
+
 2017-09-15  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* c-pragma.c (handle_pragma_scalar_storage_order): Expand on error
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index d57829b..da6a0be 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -703,7 +703,9 @@ enum cxx_dialect {
   /* C++14 */
   cxx14,
   /* C++17 */
-  cxx17
+  cxx17,
+  /* C++2a (C++20?) */
+  cxx2a
 };
 
 /* The C++ dialect being used. C++98 is the default.  */
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index cdbcd6c..3662aa3 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -111,6 +111,7 @@ static void set_std_cxx98 (int);
 static void set_std_cxx11 (int);
 static void set_std_cxx14 (int);
 static void set_std_cxx17 (int);
+static void set_std_cxx2a (int);
 static void set_std_c89 (int, int);
 static void set_std_c99 (int);
 static void set_std_c11 (int);
@@ -637,6 +638,12 @@ c_common_handle_option (size_t scode, const char *arg, int value,
 	set_std_cxx17 (code == OPT_std_c__17 /* ISO */);
       break;
 
+    case OPT_std_c__2a:
+    case OPT_std_gnu__2a:
+      if (!preprocessing_asm_p)
+	set_std_cxx2a (code == OPT_std_c__2a /* ISO */);
+      break;
+
     case OPT_std_c90:
     case OPT_std_iso9899_199409:
       if (!preprocessing_asm_p)
@@ -938,7 +945,7 @@ c_common_post_options (const char **pfilename)
 	warn_narrowing = 1;
 
       /* Unless -f{,no-}ext-numeric-literals has been used explicitly,
-	 for -std=c++{11,14,17} default to -fno-ext-numeric-literals.  */
+	 for -std=c++{11,14,17,2a} default to -fno-ext-numeric-literals.  */
       if (flag_iso && !global_options_set.x_flag_ext_numeric_literals)
 	cpp_opts->ext_numeric_literals = 0;
     }
@@ -1589,7 +1596,7 @@ set_std_cxx14 (int iso)
   flag_no_gnu_keywords = iso;
   flag_no_nonansi_builtin = iso;
   flag_iso = iso;
-  /* C++11 includes the C99 standard library.  */
+  /* C++14 includes the C99 standard library.  */
   flag_isoc94 = 1;
   flag_isoc99 = 1;
   cxx_dialect = cxx14;
@@ -1604,7 +1611,7 @@ set_std_cxx17 (int iso)
   flag_no_gnu_keywords = iso;
   flag_no_nonansi_builtin = iso;
   flag_iso = iso;
-  /* C++11 includes the C99 standard library.  */
+  /* C++17 includes the C11 standard library.  */
   flag_isoc94 = 1;
   flag_isoc99 = 1;
   flag_isoc11 = 1;
@@ -1612,6 +1619,22 @@ set_std_cxx17 (int iso)
   lang_hooks.name = "GNU C++17";
 }
 
+/* Set the C++ 202a draft standard (without GNU extensions if ISO).  */
+static void
+set_std_cxx2a (int iso)
+{
+  cpp_set_lang (parse_in, iso ? CLK_CXX2A: CLK_GNUCXX2A);
+  flag_no_gnu_keywords = iso;
+  flag_no_nonansi_builtin = iso;
+  flag_iso = iso;
+  /* C++17 includes the C11 standard library.  */
+  flag_isoc94 = 1;
+  flag_isoc99 = 1;
+  flag_isoc11 = 1;
+  cxx_dialect = cxx2a;
+  lang_hooks.name = "GNU C++17"; /* Pretend C++17 until standardization.  */
+}
+
 /* Args to -d specify what to dump.  Silently ignore
    unrecognized options; they may be aimed at toplev.c.  */
 static void
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index ed5938f..3c2c107 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1932,6 +1932,10 @@ std=c++17
 C++ ObjC++
 Conform to the ISO 2017 C++ standard.
 
+std=c++2a
+C++ ObjC++
+Conform to the ISO 2020(?) C++ draft standard (experimental and incomplete support).
+
 std=c11
 C ObjC
 Conform to the ISO 2011 C standard.
@@ -1990,6 +1994,10 @@ std=gnu++17
 C++ ObjC++
 Conform to the ISO 2017 C++ standard with GNU extensions.
 
+std=gnu++2a
+C++ ObjC++
+Conform to the ISO 2020(?) C++ draft standard with GNU extensions (experimental and incomplete support).
+
 std=gnu11
 C ObjC
 Conform to the ISO 2011 C standard with GNU extensions.
diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index 8e9cba3..52f2606 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -1877,7 +1877,10 @@ selected, the value of the macro is
 @code{199711L} for the 1998 C++ standard,
 @code{201103L} for the 2011 C++ standard,
 @code{201402L} for the 2014 C++ standard,
-@code{201703L} for the 2017 C++ standard.
+@code{201703L} for the 2017 C++ standard,
+or an unspecified value strictly larger than @code{201703L} for the
+experimental languages enabled by @option{-std=c++2a} and
+@option{-std=gnu++2a}.
 
 @item __OBJC__
 This macro is defined, with value 1, when the Objective-C compiler is in
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 60650c8..204c9b7 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1880,6 +1880,16 @@ The name @samp{c++1z} is deprecated.
 @itemx gnu++1z
 GNU dialect of @option{-std=c++17}.
 The name @samp{gnu++1z} is deprecated.
+
+@item c++2a
+The next revision of the ISO C++ standard, tentatively planned for
+2020.  Support is highly experimental, and will almost certainly
+change in incompatible ways in future releases.
+
+@item gnu++2a
+GNU dialect of @option{-std=c++2a}.  Support is highly experimental,
+and will almost certainly change in incompatible ways in future
+releases.
 @end table
 
 @item -fgnu89-inline
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index b9bb9c6..1a94535 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,14 @@
+2017-09-15  Andrew Sutton  <andrew.n.sutton@gmail.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	Add support for -std=c++2a.
+	* lib/target-supports.exp (check_effective_target_c++17): Return
+	1 also if check_effective_target_c++2a.
+	(check_effective_target_c++17_down): New.
+	(check_effective_target_c++2a_only): New.
+	(check_effective_target_c++2a): New.
+	* g++.dg/cpp2a/cplusplus.C: New.
+
 2017-09-15  Joseph Myers  <joseph@codesourcery.com>
 
 	PR c/82071
diff --git a/gcc/testsuite/g++.dg/cpp2a/cplusplus.C b/gcc/testsuite/g++.dg/cpp2a/cplusplus.C
new file mode 100644
index 0000000..614fc52
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/cplusplus.C
@@ -0,0 +1,4 @@
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+static_assert(__cplusplus > 201703L);
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index d229485..6ea7122 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -7863,8 +7863,35 @@ proc check_effective_target_c++17_only { } {
     }
     return 0
 }
+
 proc check_effective_target_c++17 { } {
-    return [check_effective_target_c++17_only]
+    if [check_effective_target_c++17_only] {
+	return 1
+    }
+    return [check_effective_target_c++2a]
+}
+proc check_effective_target_c++17_down { } {
+    if ![check_effective_target_c++] {
+	return 0
+    }
+    return [expr ![check_effective_target_c++2a] ]
+}
+
+proc check_effective_target_c++2a_only { } {
+    global cxx_default
+    if ![check_effective_target_c++] {
+	return 0
+    }
+    if [check-flags { { } { } { -std=c++2a -std=gnu++2a } }] {
+	return 1
+    }
+    if { $cxx_default == "c++20" && [check-flags { { } { } { } { -std=* } }] } {
+	return 1
+    }
+    return 0
+}
+proc check_effective_target_c++2a { } {
+    return [check_effective_target_c++2a_only]
 }
 
 # Check for C++ Concepts TS support, i.e. -fconcepts flag.