[PATCH 1/2] Add OVERRIDE and FINAL macros to coretypes.h

[David Malcolm <dmalcolm@redhat.com>]

C++11 adds the ability to add "override" after an implementation of a
virtual function in a subclass, to:
(A) document that this is an override of a virtual function
(B) allow the compiler to issue a warning if it isn't (e.g. a mismatch
of the type signature).

Similarly, it allows us to add a "final" to indicate that no subclass
may subsequently override the vfunc.

We use virtual functions in a few places (e.g. in the jit), so it would
be good to get this extra checking.

This patch adds OVERRIDE and FINAL as macros to coretypes.h
allowing us to get this extra checking when compiling with a compiler
that implements C++11 or later (e.g. gcc 6 by default),
but without requiring C++11.

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu.

OK for trunk?

Does "final" imply "override"?  Is "final override" a tautology?

gcc/ChangeLog:
	* coretypes.h (OVERRIDE): New macro.
	(FINAL): New macro.
---
 gcc/coretypes.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/coretypes.h b/gcc/coretypes.h
index 2932d73..b3a91a6 100644
--- a/gcc/coretypes.h
+++ b/gcc/coretypes.h
@@ -361,6 +361,31 @@ typedef void (*gt_pointer_operator) (void *, void *);
 typedef unsigned char uchar;
 #endif
 
+/* C++11 adds the ability to add "override" after an implementation of a
+   virtual function in a subclass, to:
+     (A) document that this is an override of a virtual function
+     (B) allow the compiler to issue a warning if it isn't (e.g. a mismatch
+         of the type signature).
+
+   Similarly, it allows us to add a "final" to indicate that no subclass
+   may subsequently override the vfunc.
+
+   Provide OVERRIDE and FINAL as macros, allowing us to get these benefits
+   when compiling with C++11 support, but without requiring C++11.
+
+   For gcc, use "-std=c++11" to enable C++11 support; gcc 6 onwards enables
+   this by default (actually GNU++14).  */
+
+#if __cplusplus >= 201103
+/* C++11 claims to be available: use it: */
+#define OVERRIDE override
+#define FINAL final
+#else
+/* No C++11 support; leave the macros empty: */
+#define OVERRIDE
+#define FINAL
+#endif
+
 /* Most host source files will require the following headers.  */
 #if !defined (GENERATOR_FILE) && !defined (USED_FOR_TARGET)
 #include "machmode.h"
-- 
1.8.5.3