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[Xen-changelog] [xen-unstable] Use unlikely() in BUG_ON()/WARN_ON()

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Subject: [Xen-changelog] [xen-unstable] Use unlikely() in BUG_ON()/WARN_ON()
From: Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>
Date: Tue, 07 Apr 2009 23:01:57 -0700
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# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1238502132 -3600
# Node ID 2fa1d38097dadddb866a4a17ad68476e9e9a7081
# Parent  4b602fff137b8c9ccd23e17c3df6423341e7757d
Use unlikely() in BUG_ON()/WARN_ON()

-fno-reorder-blocks was added in c/s 1712, when x86-64 just started to
become enabled. The reason it got added is entirely unclear to me, and
it prevents the intended effect of unlikely() constructs (in
the ones added here) of moving out of line code which is expected to
never get executed, as well as using forward branches (which are
statically predicted taken by various processors' branch prediction
units) preferably to reach infrequently executed code.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
 xen/arch/x86/Rules.mk |    2 +-
 xen/include/xen/lib.h |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff -r 4b602fff137b -r 2fa1d38097da xen/arch/x86/Rules.mk
--- a/xen/arch/x86/Rules.mk     Tue Mar 31 13:21:36 2009 +0100
+++ b/xen/arch/x86/Rules.mk     Tue Mar 31 13:22:12 2009 +0100
@@ -42,7 +42,7 @@ endif
 ifeq ($(TARGET_SUBARCH),x86_64)
-CFLAGS += -mno-red-zone -fpic -fno-reorder-blocks
+CFLAGS += -mno-red-zone -fpic
 CFLAGS += -fno-asynchronous-unwind-tables
 # -fvisibility=hidden reduces -fpic cost, if it's available
 ifneq ($(call cc-option,$(CC),-fvisibility=hidden,n),n)
diff -r 4b602fff137b -r 2fa1d38097da xen/include/xen/lib.h
--- a/xen/include/xen/lib.h     Tue Mar 31 13:21:36 2009 +0100
+++ b/xen/include/xen/lib.h     Tue Mar 31 13:22:12 2009 +0100
@@ -12,8 +12,8 @@ void __bug(char *file, int line) __attri
 void __bug(char *file, int line) __attribute__((noreturn));
 void __warn(char *file, int line);
-#define BUG_ON(p)  do { if (p) BUG();  } while (0)
-#define WARN_ON(p) do { if (p) WARN(); } while (0)
+#define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
+#define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
 /* Force a compilation error if condition is true */
 #define BUILD_BUG_ON(condition) ((void)sizeof(struct { int:-!!(condition); }))

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