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* [PATCH 1/4] powerpc: Make BUG_ON & WARN_ON play nice with compile-time optimisations
@ 2006-03-23 12:32 Michael Ellerman
  2006-03-23 12:33 ` [PATCH 2/4] powerpc: Change firmware_has_feature() to a macro Michael Ellerman
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Michael Ellerman @ 2006-03-23 12:32 UTC (permalink / raw)
  To: Paul Mackerras, linuxppc-dev

Change BUG_ON and WARN_ON to give the compiler a chance to perform
compile-time optimsations. Depending on the complexity of the condition,
the compiler may not do this very well, so if it's important check the
object code.

Current GCC's (4.x) produce good code as long as the condition does not
include a function call, including a static inline.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
---

 include/asm-powerpc/bug.h |   30 ++++++++++++++++++++++++++++--
 1 files changed, 28 insertions(+), 2 deletions(-)

Index: to-merge/include/asm-powerpc/bug.h
===================================================================
--- to-merge.orig/include/asm-powerpc/bug.h
+++ to-merge/include/asm-powerpc/bug.h
@@ -30,6 +30,12 @@ struct bug_entry *find_bug(unsigned long
 
 #ifdef CONFIG_BUG
 
+/*
+ * BUG_ON() and WARN_ON() do their best to cooperate with compile-time
+ * optimisations. However depending on the complexity of the condition
+ * some compiler versions may not produce optimal results.
+ */
+
 #define BUG() do {							 \
 	__asm__ __volatile__(						 \
 		"1:	twi 31,0,0\n"					 \
@@ -40,17 +46,36 @@ struct bug_entry *find_bug(unsigned long
 } while (0)
 
 #define BUG_ON(x) do {						\
-	__asm__ __volatile__(					\
+	if (__builtin_constant_p(x)) {				\
+		if (x)						\
+			BUG();					\
+	} else {						\
+		__asm__ __volatile__(				\
 		"1:	"PPC_TLNEI"	%0,0\n"			\
 		".section __bug_table,\"a\"\n"			\
 		"\t"PPC_LONG"	1b,%1,%2,%3\n"		\
 		".previous"					\
 		: : "r" ((long)(x)), "i" (__LINE__),		\
 		    "i" (__FILE__), "i" (__FUNCTION__));	\
+	}							\
 } while (0)
 
-#define WARN_ON(x) do {						\
+#define WARN() do {						\
 	__asm__ __volatile__(					\
+		"1:	twi 31,0,0\n"				\
+		".section __bug_table,\"a\"\n"			\
+		"\t"PPC_LONG"	1b,%0,%1,%2\n"			\
+		".previous"					\
+		: : "i" (__LINE__ + BUG_WARNING_TRAP),		\
+		    "i" (__FILE__), "i" (__FUNCTION__));	\
+} while (0)
+
+#define WARN_ON(x) do {						\
+	if (__builtin_constant_p(x)) {				\
+		if (x)						\
+			WARN();					\
+	} else {						\
+		__asm__ __volatile__(				\
 		"1:	"PPC_TLNEI"	%0,0\n"			\
 		".section __bug_table,\"a\"\n"			\
 		"\t"PPC_LONG"	1b,%1,%2,%3\n"		\
@@ -58,6 +83,7 @@ struct bug_entry *find_bug(unsigned long
 		: : "r" ((long)(x)),				\
 		    "i" (__LINE__ + BUG_WARNING_TRAP),		\
 		    "i" (__FILE__), "i" (__FUNCTION__));	\
+	}							\
 } while (0)
 
 #define HAVE_ARCH_BUG

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2006-03-23 23:40 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2006-03-23 12:32 [PATCH 1/4] powerpc: Make BUG_ON & WARN_ON play nice with compile-time optimisations Michael Ellerman
2006-03-23 12:33 ` [PATCH 2/4] powerpc: Change firmware_has_feature() to a macro Michael Ellerman
2006-03-23 12:33 ` [PATCH 3/4] powerpc: Rename and export ppc64_firmware_features Michael Ellerman
2006-03-23 13:17   ` Stephen Rothwell
2006-03-23 23:40     ` [PATCH] " Michael Ellerman
2006-03-23 12:33 ` [PATCH 4/4] powerpc: Cope with duplicate node & property names in /proc/device-tree Michael Ellerman

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