The idea is to later use these macros to mark the
if (dump_enabled_p ())
parts of the compiler as cold, in the hope of helping non-PGO builds
of gcc.
I haven't measured it yet, though.
gcc/ChangeLog:
* system.h (GCC_LIKELY, GCC_UNLIKELY): New macros, adapted from
libgfortran.h.
---
gcc/system.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/gcc/system.h b/gcc/system.h
index 88dffcc..195acb8 100644
--- a/gcc/system.h
+++ b/gcc/system.h
@@ -720,6 +720,18 @@ extern int vsnprintf (char *, size_t, const char *,
va_list);
#define __builtin_expect(a, b) (a)
#endif
+/* The following macros can be used to annotate conditions which are likely or
+ unlikely to be true. Avoid using them when a condition is only slightly
+ more likely/less unlikely than average to avoid the performance penalties of
+ branch misprediction. In addition, as __builtin_expect overrides the
compiler
+ heuristic, do not use in conditions where one of the branches ends with a
+ call to a function with __attribute__((noreturn)): the compiler internal
+ heuristic will mark this branch as much less likely as GCC_UNLIKELY() would
+ do. */
+
+#define GCC_LIKELY(X) __builtin_expect(!!(X), 1)
+#define GCC_UNLIKELY(X) __builtin_expect(!!(X), 0)
+
/* Some of the headers included by <memory> can use "abort" within a
namespace, e.g. "_VSTD::abort();", which fails after we use the
preprocessor to redefine "abort" as "fancy_abort" below.
--
1.8.5.3
