[Xen-devel] [PATCH v4 14/17] rbtree: place easiest case first in rb_erase()

[Praveen Kumar <kpraveen.lkml@xxxxxxxxx>]

From: Michel Lespinasse <walken@xxxxxxxxxx>

In rb_erase, move the easy case (node to erase has no more than
1 child) first. I feel the code reads easier that way.

Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[Linux commit 60670b8034d6e2ba860af79c9379b7788d09db73]

Ported to Xen.

Signed-off-by: Praveen Kumar <kpraveen.lkml@xxxxxxxxx>
---
 xen/common/rbtree.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index d438d50761..891f04e919 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -367,17 +367,28 @@ static void __rb_erase_color(struct rb_node *node, struct 
rb_node *parent,
 
 void rb_erase(struct rb_node *node, struct rb_root *root)
 {
-       struct rb_node *child, *parent;
+       struct rb_node *child = node->rb_right, *tmp = node->rb_left;
+       struct rb_node *parent;
        int color;
 
-       if (!node->rb_left)
-               child = node->rb_right;
-       else if (!node->rb_right)
-               child = node->rb_left;
-       else {
+       if (!tmp) {
+       case1:
+               /* Case 1: node to erase has no more than 1 child (easy!) */
+
+               parent = rb_parent(node);
+               color = rb_color(node);
+
+               if (child)
+                       rb_set_parent(child, parent);
+               __rb_change_child(node, child, parent, root);
+       } else if (!child) {
+               /* Still case 1, but this time the child is node->rb_left */
+               child = tmp;
+               goto case1;
+       } else {
                struct rb_node *old = node, *left;
 
-               node = node->rb_right;
+               node = child;
                while ((left = node->rb_left) != NULL)
                        node = left;
 
@@ -402,18 +413,8 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
                node->rb_left = old->rb_left;
 
                rb_set_parent(old->rb_left, node);
-
-               goto color;
        }
 
-       parent = rb_parent(node);
-       color = rb_color(node);
-
-       if (child)
-               rb_set_parent(child, parent);
-       __rb_change_child(node, child, parent, root);
-
-color:
        if (color == RB_BLACK)
                __rb_erase_color(child, parent, root);
 }
-- 
2.12.0


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