linux-kernel - [PATCH] Optimization of function rb

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Date:	Sat, 24 Jan 2009 13:32:34 +0100
From:	"Wolfram Strepp" <wstrepp@....de>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, dwmw2@...radead.org,
	akpm@...ux-foundation.org
Subject: [PATCH] Optimization of function rb_erase() in lib/rbtree.c

In the patch below, 4 redundant if-conditions in function __rb_erase_color() in lib/rbtree.c are removed.  
Here an explanation for it. In pseudo-source-code, the
structure of the code is as follows: 
 

if ((!A || B) && (!C || D)) {
	.
	.
	.
} else {
	if (!C || D) {//if this is true, it implies: (A == true) && (B == false)
		if (A) {//hence this always evaluates to 'true'...
			.
		}
		.
		//at this point, C always becomes true, because of:
		__rb_rotate_right/left();
		//and:
		other = parent->rb_right/left;
	}
	.
	.
	if (C) {//...and this too !
		.
	}
}

Signed-off-by: Wolfram Strepp <wstrepp@....de>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

================================================
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -163,17 +163,14 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 			{
 				if (!other->rb_right || rb_is_black(other->rb_right))
 				{
-					struct rb_node *o_left;
-					if ((o_left = other->rb_left))
-						rb_set_black(o_left);
+					rb_set_black(other->rb_left);
 					rb_set_red(other);
 					__rb_rotate_right(other, root);
 					other = parent->rb_right;
 				}
 				rb_set_color(other, rb_color(parent));
 				rb_set_black(parent);
-				if (other->rb_right)
-					rb_set_black(other->rb_right);
+				rb_set_black(other->rb_right);
 				__rb_rotate_left(parent, root);
 				node = root->rb_node;
 				break;
@@ -200,17 +197,14 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 			{
 				if (!other->rb_left || rb_is_black(other->rb_left))
 				{
-					register struct rb_node *o_right;
-					if ((o_right = other->rb_right))
-						rb_set_black(o_right);
+					rb_set_black(other->rb_right);
 					rb_set_red(other);
 					__rb_rotate_left(other, root);
 					other = parent->rb_left;
 				}
 				rb_set_color(other, rb_color(parent));
 				rb_set_black(parent);
-				if (other->rb_left)
-					rb_set_black(other->rb_left);
+				rb_set_black(other->rb_left);
 				__rb_rotate_right(parent, root);
 				node = root->rb_node;
 				break;


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