lib/rbtree.c: optimize rb_erase()

Tfour 4 redundant if-conditions in function __rb_erase_color() in
lib/rbtree.c are removed.

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@gmx.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <andrea@qumranet.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/rbtree.c b/lib/rbtree.c
index 9956b99..f653659 100644 (file)
--- 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;