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Subject[PATCH 12/13] rbtree: optimize tree rotations in __rb_erase_color()
Date
In __rb_erase_color(), we often already have pointers to the nodes
being rotated and/or know what their colors must be, so we can
generate more efficient code than the generic __rb_rotate_left()
and __rb_rotate_right() functions.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
lib/rbtree.c | 154 ++++++++++++++++++++++++---------------------------------
1 files changed, 65 insertions(+), 89 deletions(-)
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 597c1b9..c956248 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -36,10 +36,6 @@ static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
{
rb->rb_parent_color = (rb->rb_parent_color & 3) | (unsigned long)p;
}
-static inline void rb_set_color(struct rb_node *rb, int color)
-{
- rb->rb_parent_color = (rb->rb_parent_color & ~1) | color;
-}

static inline void rb_set_parent_color(struct rb_node *rb,
struct rb_node *p, int color)
@@ -52,52 +48,6 @@ static inline struct rb_node *rb_red_parent(struct rb_node *red)
return (struct rb_node *)red->rb_parent_color;
}

-static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)
-{
- struct rb_node *right = node->rb_right;
- struct rb_node *parent = rb_parent(node);
-
- if ((node->rb_right = right->rb_left))
- rb_set_parent(right->rb_left, node);
- right->rb_left = node;
-
- rb_set_parent(right, parent);
-
- if (parent)
- {
- if (node == parent->rb_left)
- parent->rb_left = right;
- else
- parent->rb_right = right;
- }
- else
- root->rb_node = right;
- rb_set_parent(node, right);
-}
-
-static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
-{
- struct rb_node *left = node->rb_left;
- struct rb_node *parent = rb_parent(node);
-
- if ((node->rb_left = left->rb_right))
- rb_set_parent(left->rb_right, node);
- left->rb_right = node;
-
- rb_set_parent(left, parent);
-
- if (parent)
- {
- if (node == parent->rb_right)
- parent->rb_right = left;
- else
- parent->rb_left = left;
- }
- else
- root->rb_node = left;
- rb_set_parent(node, left);
-}
-
/*
* Helper function for rotations:
* - old's parent and color get assigned to new
@@ -207,7 +157,7 @@ EXPORT_SYMBOL(rb_insert_color);
static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
struct rb_root *root)
{
- struct rb_node *other;
+ struct rb_node *sibling, *tmp1, *tmp2;

while (true) {
/*
@@ -225,58 +175,84 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
} else if (!parent) {
break;
} else if (parent->rb_left == node) {
- other = parent->rb_right;
- if (rb_is_red(other))
- {
- rb_set_black(other);
- rb_set_red(parent);
- __rb_rotate_left(parent, root);
- other = parent->rb_right;
+ sibling = parent->rb_right;
+ if (rb_is_red(sibling)) {
+ /* Case 1 - left rotate at parent */
+ parent->rb_right = tmp1 = sibling->rb_left;
+ sibling->rb_left = parent;
+ rb_set_parent_color(tmp1, parent, RB_BLACK);
+ __rb_rotate_set_parents(parent, sibling, root,
+ RB_RED);
+ sibling = tmp1;
}
- if (!other->rb_right || rb_is_black(other->rb_right)) {
- if (!other->rb_left ||
- rb_is_black(other->rb_left)) {
- rb_set_red(other);
+ tmp1 = sibling->rb_right;
+ if (!tmp1 || rb_is_black(tmp1)) {
+ tmp2 = sibling->rb_left;
+ if (!tmp2 || rb_is_black(tmp2)) {
+ /* Case 2 - sibling color flip */
+ rb_set_red(sibling);
node = parent;
parent = rb_parent(node);
continue;
}
- rb_set_black(other->rb_left);
- rb_set_red(other);
- __rb_rotate_right(other, root);
- other = parent->rb_right;
+ /* Case 3 - right rotate at sibling */
+ sibling->rb_left = tmp1 = tmp2->rb_right;
+ tmp2->rb_right = sibling;
+ parent->rb_right = tmp2;
+ if (tmp1)
+ rb_set_parent_color(tmp1, sibling,
+ RB_BLACK);
+ tmp1 = sibling;
+ sibling = tmp2;
}
- rb_set_color(other, rb_color(parent));
- rb_set_black(parent);
- rb_set_black(other->rb_right);
- __rb_rotate_left(parent, root);
+ /* Case 4 - left rotate at parent + color flips */
+ parent->rb_right = tmp2 = sibling->rb_left;
+ sibling->rb_left = parent;
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ if (tmp2)
+ rb_set_parent(tmp2, parent);
+ __rb_rotate_set_parents(parent, sibling, root,
+ RB_BLACK);
break;
} else {
- other = parent->rb_left;
- if (rb_is_red(other))
- {
- rb_set_black(other);
- rb_set_red(parent);
- __rb_rotate_right(parent, root);
- other = parent->rb_left;
+ sibling = parent->rb_left;
+ if (rb_is_red(sibling)) {
+ /* Case 1 - right rotate at parent */
+ parent->rb_left = tmp1 = sibling->rb_right;
+ sibling->rb_right = parent;
+ rb_set_parent_color(tmp1, parent, RB_BLACK);
+ __rb_rotate_set_parents(parent, sibling, root,
+ RB_RED);
+ sibling = tmp1;
}
- if (!other->rb_left || rb_is_black(other->rb_left)) {
- if (!other->rb_right ||
- rb_is_black(other->rb_right)) {
- rb_set_red(other);
+ tmp1 = sibling->rb_left;
+ if (!tmp1 || rb_is_black(tmp1)) {
+ tmp2 = sibling->rb_right;
+ if (!tmp2 || rb_is_black(tmp2)) {
+ /* Case 2 - sibling color flip */
+ rb_set_red(sibling);
node = parent;
parent = rb_parent(node);
continue;
}
- rb_set_black(other->rb_right);
- rb_set_red(other);
- __rb_rotate_left(other, root);
- other = parent->rb_left;
+ /* Case 3 - right rotate at sibling */
+ sibling->rb_right = tmp1 = tmp2->rb_left;
+ tmp2->rb_left = sibling;
+ parent->rb_left = tmp2;
+ if (tmp1)
+ rb_set_parent_color(tmp1, sibling,
+ RB_BLACK);
+ tmp1 = sibling;
+ sibling = tmp2;
}
- rb_set_color(other, rb_color(parent));
- rb_set_black(parent);
- rb_set_black(other->rb_left);
- __rb_rotate_right(parent, root);
+ /* Case 4 - left rotate at parent + color flips */
+ parent->rb_left = tmp2 = sibling->rb_right;
+ sibling->rb_right = parent;
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ if (tmp2)
+ rb_set_parent(tmp2, parent);
+ __rb_rotate_set_parents(parent, sibling, root,
+ RB_BLACK);
break;
}
}
--
1.7.7.3


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