linux-kernel - [PATCH] min/max: remove sparse warnings when they're nested

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Date:	Thu, 18 Aug 2016 13:29:33 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Johannes Berg <johannes.berg@...el.com>
Subject: [PATCH] min/max: remove sparse warnings when they're nested

From: Johannes Berg <johannes.berg@...el.com>

Currently, when min/max are nested within themselves, sparse
will warn:

    warning: symbol '_min1' shadows an earlier one
    originally declared here
    warning: symbol '_min1' shadows an earlier one
    originally declared here
    warning: symbol '_min2' shadows an earlier one
    originally declared here

This also immediately happens when min3() or max3() are used.

Since sparse implements __COUNTER__, we can use __UNIQUE_ID()
to generate unique variable names, avoiding this.

Signed-off-by: Johannes Berg <johannes.berg@...el.com>
---
So I'm on a bit of a quest to quell useless sparse warnings.
Maybe this is over the top... it does seem to work though :)
---
 include/linux/kernel.h | 48 ++++++++++++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d96a6118d26a..853c4bf027ea 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -736,17 +736,25 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
  * strict type-checking.. See the
  * "unnecessary" pointer comparison.
  */
-#define min(x, y) ({				\
-	typeof(x) _min1 = (x);			\
-	typeof(y) _min2 = (y);			\
-	(void) (&_min1 == &_min2);		\
-	_min1 < _min2 ? _min1 : _min2; })
-
-#define max(x, y) ({				\
-	typeof(x) _max1 = (x);			\
-	typeof(y) _max2 = (y);			\
-	(void) (&_max1 == &_max2);		\
-	_max1 > _max2 ? _max1 : _max2; })
+#define __min(t1, t2, min1, min2, x, y) ({		\
+	t1 min1 = (x);					\
+	t2 min2 = (y);					\
+	(void) (&min1 == &min2);			\
+	min1 < min2 ? min1 : min2; })
+#define min(x, y)					\
+	__min(typeof(x), typeof(y),			\
+	      __UNIQUE_ID(min1_), __UNIQUE_ID(min2_),	\
+	      x, y)
+
+#define __max(t1, t2, max1, max2, x, y) ({		\
+	t1 max1 = (x);					\
+	t2 max2 = (y);					\
+	(void) (&max1 == &max2);			\
+	max1 > max2 ? max1 : max2; })
+#define max(x, y)					\
+	__max(typeof(x), typeof(y),			\
+	      __UNIQUE_ID(max1_), __UNIQUE_ID(max2_),	\
+	      x, y)
 
 #define min3(x, y, z) min((typeof(x))min(x, y), z)
 #define max3(x, y, z) max((typeof(x))max(x, y), z)
@@ -778,15 +786,15 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
  *
  * Or not use min/max/clamp at all, of course.
  */
-#define min_t(type, x, y) ({			\
-	type __min1 = (x);			\
-	type __min2 = (y);			\
-	__min1 < __min2 ? __min1: __min2; })
-
-#define max_t(type, x, y) ({			\
-	type __max1 = (x);			\
-	type __max2 = (y);			\
-	__max1 > __max2 ? __max1: __max2; })
+#define min_t(type, x, y)				\
+	__min(type, type,				\
+	      __UNIQUE_ID(min1_), __UNIQUE_ID(min2_),	\
+	      x, y)
+
+#define max_t(type, x, y)				\
+	__max(type, type,				\
+	      __UNIQUE_ID(min1_), __UNIQUE_ID(min2_),	\
+	      x, y)
 
 /**
  * clamp_t - return a value clamped to a given range using a given type
-- 
2.8.1