From 732b31de5d9244bd1cc98192e09ee1881e9f55e9 Mon Sep 17 00:00:00 2001
From: "Pedro F. Giffuni" <pfg@FreeBSD.org>
Date: Thu, 14 May 2015 15:49:48 +0000
Subject: [PATCH] Add new __unreachable() builtin

This is one of the few post gcc4.2 builtins that has been implemented by
clang:

__builtin_unreachable is used to indicate that a specific point in the
program cannot be reached, even if the compiler might otherwise think it
can. This is useful to improve optimization and eliminates certain
warnings.

Hinted by:	NetBSD
Differential Revision:	https://reviews.freebsd.org/D2536
---
 sys/sys/cdefs.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index a7286ab7aa08..73734cb11067 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -388,6 +388,12 @@
 #define	__alloc_size(x)
 #endif
 
+#if __has_builtin(__builtin_unreachable) || __GNUC_PREREQ__(4, 6)
+#define	__unreachable()	__builtin_unreachable()
+#else
+#define	__unreachable()	do {} while (/*CONSTCOND*/0)
+#endif
+
 #if __has_attribute(alloc_align) || __GNUC_PREREQ__(4, 9)
 #define	__alloc_align(x)	__attribute__((__alloc_align__(x)))
 #else