From c807b9ec0672e1217136c8d0748c2f9affb77ad7 Mon Sep 17 00:00:00 2001
From: Doug Moore <dougm@FreeBSD.org>
Date: Thu, 21 May 2020 05:34:02 +0000
Subject: [PATCH] For the case when RB_REMOVE requires a nontrivial search to
 find the node to replace the one being removed, restructure to first remove
 the replacement node and correct the parent pointers around it, and then let
 the all-cases code at the end deal with the parent of the deleted node,
 making it point to the replacement node. This removes one or two conditional
 branches.

Reviewed by:	markj
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D24845
---
 sys/sys/tree.h | 52 +++++++++++++++++++++++---------------------------
 1 file changed, 24 insertions(+), 28 deletions(-)

diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index df85b0587570..0c228df5a926 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -562,48 +562,44 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent, struct type *elm)
 attr struct type *							\
 name##_RB_REMOVE(struct name *head, struct type *elm)			\
 {									\
-	struct type *child, *parent, *old = elm;			\
+	struct type *child, *parent, *parent_old, *old = elm;		\
 	int color;							\
-	if (RB_LEFT(elm, field) == NULL)				\
-		child = RB_RIGHT(elm, field);				\
-	else if (RB_RIGHT(elm, field) == NULL)				\
-		child = RB_LEFT(elm, field);				\
-	else {								\
+	parent_old = parent = RB_PARENT(elm, field);			\
+	color = RB_COLOR(elm, field);					\
+	if (RB_LEFT(elm, field) == NULL) {				\
+		elm = child = RB_RIGHT(elm, field);			\
+		if (elm != NULL)					\
+			RB_PARENT(elm, field) = parent;			\
+	} else if (RB_RIGHT(elm, field) == NULL) {			\
+		elm = child = RB_LEFT(elm, field);			\
+		RB_PARENT(elm, field) = parent;				\
+	} else {							\
 		elm = RB_RIGHT(old, field);				\
 		if ((child = RB_LEFT(elm, field)) == NULL) {		\
 			child = RB_RIGHT(elm, field);			\
 			RB_RIGHT(old, field) = child;			\
-			RB_PARENT(elm, field) = elm;			\
+			parent = elm;					\
 		} else {						\
 			do						\
 				elm = child;				\
 			while ((child = RB_LEFT(elm, field)) != NULL);	\
 			child = RB_RIGHT(elm, field);			\
+			parent = RB_PARENT(elm, field);			\
+			RB_LEFT(parent, field) = child;			\
+			if (child != NULL)				\
+				RB_PARENT(child, field) = parent;	\
 			RB_PARENT(RB_RIGHT(old, field), field) = elm;	\
 		}							\
 		RB_PARENT(RB_LEFT(old, field), field) = elm;		\
-		parent = RB_PARENT(old, field);				\
-		if (parent != NULL) {					\
-			if (RB_LEFT(parent, field) == old)		\
-				RB_LEFT(parent, field) = elm;		\
-			else						\
-				RB_RIGHT(parent, field) = elm;		\
-		} else							\
-			RB_ROOT(head) = elm;				\
+		color = RB_COLOR(elm, field);				\
+		elm->field = old->field;				\
 	}								\
-	parent = RB_PARENT(elm, field);					\
-	color = RB_COLOR(elm, field);					\
-	if (child != NULL)						\
-		RB_PARENT(child, field) = parent;			\
-	if (parent != NULL) {						\
-		if (RB_LEFT(parent, field) == elm)			\
-			RB_LEFT(parent, field) = child;			\
-		else							\
-			RB_RIGHT(parent, field) = child;		\
-	} else								\
-		RB_ROOT(head) = child;					\
-	if (elm != old)							\
-		(elm)->field = (old)->field;				\
+	if (parent_old == NULL)						\
+		RB_ROOT(head) = elm;					\
+	else if (RB_LEFT(parent_old, field) == old)			\
+		RB_LEFT(parent_old, field) = elm;			\
+	else								\
+		RB_RIGHT(parent_old, field) = elm;			\
 	if (color == RB_BLACK)						\
 		name##_RB_REMOVE_COLOR(head, parent, child);		\
 	while (parent != NULL) {					\