[PATCH 3/3] debug.h: hint a compiler: TRACE is not executed in common usage

[Konstantin Kharlamov]

Below are results of running "the big keybench" benchmark of Xonotic
under "perf".  They're negligible, still, it might make more difference
for slower machines or distinct workloads.

branch-misses:
vanilla-wine  | patched-wine  | improvement
------------------------------|------------
1,757,439,276 | 1,749,075,739 |  -8,363,537
1,750,670,918 | 1,746,169,971 |  -4,500,947
1,746,488,762 | 1,748,569,739 |   2,080,977
1,753,328,811 | 1,739,515,555 | -13,813,256

Command line example for testing:
export WINEPREFIX=~/.wineTESTING; perf stat -B -e cache-misses,branch-misses,faults ~/Projects/wine/test-build/loader/wine ./xonotic-x86.exe -benchmark demos/the-big-keybench

Signed-off-by: Konstantin Kharlamov <Hi-Angel at yandex.ru>
---
 include/windef.h     | 9 +++++++++
 include/wine/debug.h | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/windef.h b/include/windef.h
index f9a570d9cd..6d1c348d47 100644
--- a/include/windef.h
+++ b/include/windef.h
@@ -35,6 +35,15 @@
 extern "C" {
 #endif
 
+/* Branch hints for performance critical code */
+#ifdef __GNUC__
+#define __likely(expr) (__builtin_expect(expr, 1))
+#define __unlikely(expr) (__builtin_expect(expr, 0))
+#else
+#define __likely(expr) (expr)
+#define __unlikely(expr) (expr)
+#endif
+
 /* Calling conventions definitions */
 
 #if (defined(__x86_64__) || defined(__powerpc64__) || defined(__aarch64__)) && !defined(_WIN64)
diff --git a/include/wine/debug.h b/include/wine/debug.h
index e9ec81c623..e13376d6db 100644
--- a/include/wine/debug.h
+++ b/include/wine/debug.h
@@ -58,7 +58,7 @@ struct __wine_debug_channel
 };
 
 #ifndef WINE_NO_TRACE_MSGS
-# define __WINE_GET_DEBUGGING_TRACE(dbch) ((dbch)->flags & (1 << __WINE_DBCL_TRACE))
+# define __WINE_GET_DEBUGGING_TRACE(dbch) __unlikely((dbch)->flags & (1 << __WINE_DBCL_TRACE))
 # define WINE_TRACE                 __WINE_DPRINTF(_TRACE,__wine_dbch___default)
 # define WINE_TRACE_(ch)            __WINE_DPRINTF(_TRACE,&__wine_dbch_##ch)
 #else
-- 
2.20.1