Mesa (master): util: Add assume() macro.

[Matt Turner]

Module: Mesa
Branch: master
Commit: 2695891088d5b910edd9ec4d3ad81f0e3469205c
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=2695891088d5b910edd9ec4d3ad81f0e3469205c

Author: Matt Turner <mattst88 at gmail.com>
Date:   Tue Sep 30 16:24:39 2014 -0700

util: Add assume() macro.

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

---

 src/util/macros.h |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/util/macros.h b/src/util/macros.h
index 40ebf02..ff37a7d 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -75,6 +75,20 @@ do {                        \
 #define unreachable(str)
 #endif
 
+/**
+ * Assume macro. Useful for expressing our assumptions to the compiler,
+ * typically for purposes of silencing warnings.
+ */
+#ifdef HAVE___BUILTIN_UNREACHABLE
+#define assume(expr) ((expr) ? ((void) 0) \
+                             : (assert(!"assumption failed"), \
+                                __builtin_unreachable()))
+#elif _MSC_VER >= 1200
+#define assume(expr) __assume(expr)
+#else
+#define assume(expr) assert(expr)
+#endif
+
 #ifdef HAVE_FUNC_ATTRIBUTE_FLATTEN
 #define FLATTEN __attribute__((__flatten__))
 #else