Re: clang and _Noreturn

[Paul Eggert]

Bruno Haible wrote:

> 1) If _Noreturn does not apply to function pointers, only to functions, we
>    should better avoid it. It's an ill-defined standard's feature.

Hmm, well, we cannot avoid _Noreturn in general, since the standard requires it 
for functions defined by the standard. Admittedly this incompatibility between 
_Noreturn and __attribute__ ((__noreturn__)) is a pain.

> So, at least for obstack.c, I propose to be consistent: use only
> __attribute__ ((__noreturn__)).

Although this will work for GCC and Clang, I suppose it might cause other 
compilers to generate slightly-less-efficient code, because they won't know that 
print_and_abort does not return. To avoid that problem, how about this further 
patch? If we run into this problem elsewhere we can move the Noreturn macro to a 
more-public location.

2017-04-23  Paul Eggert  <address@hidden>

        obstack: tweak noreturn for non-GCC
        * lib/obstack.c (Noreturn): New macro.
        (print_and_abort): Use it.

diff --git a/lib/obstack.c b/lib/obstack.c
index 49a846c..9399d4e 100644
--- a/lib/obstack.c
+++ b/lib/obstack.c
@@ -326,7 +326,18 @@ int obstack_exit_failure = EXIT_FAILURE;
 #   include <libio/iolibio.h>
 #  endif

-static __attribute_noreturn__ void
+/* Attribute for defining a function that does not return and whose
+   address can be assigned to an __attribute_noreturn__ function
+   pointer.  __attribute_noreturn__ is required for compilers that
+   grok __attribute__ ((__noreturn__)) and _Noreturn might help
+   compilers that do not.  */
+#if 2 < __GNUC__ + (8 <= __GNUC_MINOR__) || 0x5110 <= __SUNPRO_C
+# define Noreturn __attribute_noreturn__
+#else
+# define Noreturn _Noreturn
+#endif
+
+static Noreturn void
 print_and_abort (void)
 {
   /* Don't change any of these strings.  Yes, it would be possible to add