[PATCH 0/4] Optimize red-black tree insert/extract

[PATCH 0/4] Optimize red-black tree insert/extract

[Sebastian Huber]

Code coverage analysis of the red-black tree insert/extract operations defined
in <sys/tree.h> showed that the macros contain dead code.  This patch set
simplifies some expressions and add specialized rotations.

Sebastian Huber (4):
  sys/tree.h: Simplify loop condition
  sys/tree.h: Simplify chain of conditions
  sys/tree.h: Add parent rotations
  sys/tree.h: Red child with black sibling rotations

 newlib/libc/include/sys/tree.h | 66 +++++++++++++++++++++++++++++-----
 1 file changed, 58 insertions(+), 8 deletions(-)

-- 
2.26.2

[PATCH 1/4] sys/tree.h: Simplify loop condition

[Sebastian Huber]

We have

  #define RB_ISRED(elm, field) \
    ((elm) != NULL && RB_COLOR(elm, field) == RB_RED)

So, the RB_ISRED() contains an implicit check for NULL.  In
RB_GENERATE_REMOVE_COLOR() the "elm" pointer cannot be NULL in the while
condition.  Use RB_COLOR(elm) == RB_BLACK instead.
---
 newlib/libc/include/sys/tree.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/newlib/libc/include/sys/tree.h b/newlib/libc/include/sys/tree.h
index 2af77a499..15831c7dd 100644
--- a/newlib/libc/include/sys/tree.h
+++ b/newlib/libc/include/sys/tree.h
@@ -540,7 +540,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 			elm = RB_ROOT(head);				\
 			break;						\
 		}							\
-	} while (!RB_ISRED(elm, field) && parent != NULL);		\
+	} while (RB_COLOR(elm, field) == RB_BLACK && parent != NULL);	\
 	RB_COLOR(elm, field) = RB_BLACK;				\
 }
 
-- 
2.26.2

[PATCH 2/4] sys/tree.h: Simplify chain of conditions

[Sebastian Huber]

In RB_GENERATE_REMOVE_COLOR() simplify a chain of conditions of the following
pattern

if (x) {
  ...
} else if (!x) {
  ...
}

to

if (x) {
  ...
} else {
  ...
}
---
 newlib/libc/include/sys/tree.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/newlib/libc/include/sys/tree.h b/newlib/libc/include/sys/tree.h
index 15831c7dd..180809e9b 100644
--- a/newlib/libc/include/sys/tree.h
+++ b/newlib/libc/include/sys/tree.h
@@ -528,7 +528,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 				RB_ROTATE_LEFT(head, tmp, oright, field); \
 				RB_COLOR(oright, field) = RB_BLACK;	\
 				tmp = oright;				\
-			} else if (!RB_ISRED(RB_LEFT(tmp, field), field)) { \
+			} else {					\
 				RB_COLOR(tmp, field) = RB_RED;		\
 				elm = parent;				\
 				parent = RB_PARENT(elm, field);		\
-- 
2.26.2

[PATCH 3/4] sys/tree.h: Add parent rotations

[Sebastian Huber]

Add specialized rotations RB_PARENT_ROTATE_LEFT() and RB_PARENT_ROTATE_RIGHT()
which may be used if the parent node exists and the direction of the child is
known.  The specialized rotations are derived from RB_ROTATE_LEFT() and
RB_ROTATE_RIGHT() where the RB_SWAP_CHILD() was replaced by a simple
assignment.
---
 newlib/libc/include/sys/tree.h | 36 ++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/newlib/libc/include/sys/tree.h b/newlib/libc/include/sys/tree.h
index 180809e9b..5fc052817 100644
--- a/newlib/libc/include/sys/tree.h
+++ b/newlib/libc/include/sys/tree.h
@@ -381,6 +381,30 @@ struct {								\
 	RB_AUGMENT(elm);						\
 } while (/*CONSTCOND*/ 0)
 
+#define RB_PARENT_ROTATE_LEFT(parent, left, tmp, field) do {		\
+	(tmp) = RB_RIGHT(left, field);					\
+	if ((RB_RIGHT(left, field) = RB_LEFT(tmp, field)) != NULL) {	\
+		RB_SET_PARENT(RB_RIGHT(left, field), left, field);	\
+	}								\
+	RB_SET_PARENT(tmp, parent, field);				\
+	RB_LEFT(parent, field) = (tmp);					\
+	RB_LEFT(tmp, field) = (left);					\
+	RB_SET_PARENT(left, tmp, field);				\
+	RB_AUGMENT(left);						\
+} while (/*CONSTCOND*/ 0)
+
+#define RB_PARENT_ROTATE_RIGHT(parent, elm, tmp, field) do {		\
+	(tmp) = RB_LEFT(elm, field);					\
+	if ((RB_LEFT(elm, field) = RB_RIGHT(tmp, field)) != NULL) {	\
+		RB_SET_PARENT(RB_LEFT(elm, field), elm, field);		\
+	}								\
+	RB_SET_PARENT(tmp, parent, field);				\
+	RB_RIGHT(parent, field) = (tmp);				\
+	RB_RIGHT(tmp, field) = (elm);					\
+	RB_SET_PARENT(elm, tmp, field);					\
+	RB_AUGMENT(elm);						\
+} while (/*CONSTCOND*/ 0)
+
 /* Generates prototypes and inline functions */
 #define	RB_PROTOTYPE(name, type, field, cmp)				\
 	RB_PROTOTYPE_INTERNAL(name, type, field, cmp,)
@@ -454,7 +478,8 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm)		\
 				continue;				\
 			}						\
 			if (RB_RIGHT(parent, field) == elm) {		\
-				RB_ROTATE_LEFT(head, parent, tmp, field);\
+				RB_PARENT_ROTATE_LEFT(gparent, parent,	\
+				    tmp, field);			\
 				tmp = parent;				\
 				parent = elm;				\
 				elm = tmp;				\
@@ -470,7 +495,8 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm)		\
 				continue;				\
 			}						\
 			if (RB_LEFT(parent, field) == elm) {		\
-				RB_ROTATE_RIGHT(head, parent, tmp, field);\
+				RB_PARENT_ROTATE_RIGHT(gparent, parent,	\
+				    tmp, field);			\
 				tmp = parent;				\
 				parent = elm;				\
 				elm = tmp;				\
@@ -500,7 +526,8 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 				RB_COLOR(RB_RIGHT(tmp, field), field) = RB_BLACK; \
 			else if (RB_ISRED(RB_LEFT(tmp, field), field)) { \
 				struct type *oleft;			\
-				RB_ROTATE_RIGHT(head, tmp, oleft, field); \
+				RB_PARENT_ROTATE_RIGHT(parent, tmp,	\
+				    oleft, field);			\
 				RB_COLOR(oleft, field) = RB_BLACK;	\
 				tmp = oleft;				\
 			} else {					\
@@ -525,7 +552,8 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 				RB_COLOR(RB_LEFT(tmp, field), field) = RB_BLACK; \
 			else if (RB_ISRED(RB_RIGHT(tmp, field), field)) { \
 				struct type *oright;			\
-				RB_ROTATE_LEFT(head, tmp, oright, field); \
+				RB_PARENT_ROTATE_LEFT(parent, tmp,	\
+				    oright, field);			\
 				RB_COLOR(oright, field) = RB_BLACK;	\
 				tmp = oright;				\
 			} else {					\
-- 
2.26.2

[PATCH 4/4] sys/tree.h: Red child with black sibling rotations

[Sebastian Huber]

Add specialized rotations RB_RED_ROTATE_LEFT() and RB_RED_ROTATE_RIGHT() which
may be used if we rotate a red child which has a black sibling.  Such a red
node must have at least two child nodes so that the following red-black tree
invariant is fulfilled:

  Every path from a given node to any of its descendant NULL nodes goes through
  the same number of black nodes.

      PARENT
     /      \
  BLACK     RED
           /   \
        BLACK BLACK
---
 newlib/libc/include/sys/tree.h | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/newlib/libc/include/sys/tree.h b/newlib/libc/include/sys/tree.h
index 5fc052817..ae5e620c9 100644
--- a/newlib/libc/include/sys/tree.h
+++ b/newlib/libc/include/sys/tree.h
@@ -405,6 +405,28 @@ struct {								\
 	RB_AUGMENT(elm);						\
 } while (/*CONSTCOND*/ 0)
 
+#define RB_RED_ROTATE_LEFT(head, elm, tmp, field) do {			\
+	(tmp) = RB_RIGHT(elm, field);					\
+	RB_RIGHT(elm, field) = RB_LEFT(tmp, field);			\
+	RB_SET_PARENT(RB_RIGHT(elm, field), elm, field);		\
+	RB_SET_PARENT(tmp, RB_PARENT(elm, field), field);		\
+	RB_SWAP_CHILD(head, elm, tmp, field);				\
+	RB_LEFT(tmp, field) = (elm);					\
+	RB_SET_PARENT(elm, tmp, field);					\
+	RB_AUGMENT(elm);						\
+} while (/*CONSTCOND*/ 0)
+
+#define RB_RED_ROTATE_RIGHT(head, elm, tmp, field) do {			\
+	(tmp) = RB_LEFT(elm, field);					\
+	RB_LEFT(elm, field) = RB_RIGHT(tmp, field);			\
+	RB_SET_PARENT(RB_LEFT(elm, field), elm, field);			\
+	RB_SET_PARENT(tmp, RB_PARENT(elm, field), field);		\
+	RB_SWAP_CHILD(head, elm, tmp, field);				\
+	RB_RIGHT(tmp, field) = (elm);					\
+	RB_SET_PARENT(elm, tmp, field);					\
+	RB_AUGMENT(elm);						\
+} while (/*CONSTCOND*/ 0)
+
 /* Generates prototypes and inline functions */
 #define	RB_PROTOTYPE(name, type, field, cmp)				\
 	RB_PROTOTYPE_INTERNAL(name, type, field, cmp,)
@@ -519,7 +541,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 			tmp = RB_RIGHT(parent, field);			\
 			if (RB_COLOR(tmp, field) == RB_RED) {		\
 				RB_SET_BLACKRED(tmp, parent, field);	\
-				RB_ROTATE_LEFT(head, parent, tmp, field);\
+				RB_RED_ROTATE_LEFT(head, parent, tmp, field); \
 				tmp = RB_RIGHT(parent, field);		\
 			}						\
 			if (RB_ISRED(RB_RIGHT(tmp, field), field))	\
@@ -545,7 +567,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type *parent)		\
 			tmp = RB_LEFT(parent, field);			\
 			if (RB_COLOR(tmp, field) == RB_RED) {		\
 				RB_SET_BLACKRED(tmp, parent, field);	\
-				RB_ROTATE_RIGHT(head, parent, tmp, field);\
+				RB_RED_ROTATE_RIGHT(head, parent, tmp, field); \
 				tmp = RB_LEFT(parent, field);		\
 			}						\
 			if (RB_ISRED(RB_LEFT(tmp, field), field))	\
-- 
2.26.2

Re: Fw: [PATCH 3/4] sys/tree.h: Add parent rotations

[C Howland]

>
>
>
> ------------------------------
> *From:* Newlib <newlib-bounces+craig.howland=caci.com@sourceware.org> on
> behalf of Sebastian Huber <sebastian.huber@embedded-brains.de>
> *Sent:* Tuesday, October 5, 2021 10:16 AM
> *To:* newlib@sourceware.org <newlib@sourceware.org>
> *Cc:* devel@rtems.org <devel@rtems.org>
> *Subject:* [PATCH 3/4] sys/tree.h: Add parent rotations
>
>
>
> Add specialized rotations RB_PARENT_ROTATE_LEFT() and
> RB_PARENT_ROTATE_RIGHT()
> which may be used if the parent node exists and the direction of the child
> is
> known.  The specialized rotations are derived from RB_ROTATE_LEFT() and
> RB_ROTATE_RIGHT() where the RB_SWAP_CHILD() was replaced by a simple
> assignment.
>

It would seem appropriate for both this patch and #4 to include your
descriptions from the emails about the specialized nature of these new
macros in the source.  (Otherwise, how can the conditions on their use be
known?)
Craig

---
>  newlib/libc/include/sys/tree.h | 36 ++++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/newlib/libc/include/sys/tree.h
> b/newlib/libc/include/sys/tree.h
> index 180809e9b..5fc052817 100644
> --- a/newlib/libc/include/sys/tree.h
> +++ b/newlib/libc/include/sys/tree.h
> @@ -381,6 +381,30 @@ struct
> {                                                           \
>         RB_AUGMENT(elm);                                                \
>  } while (/*CONSTCOND*/ 0)
>
> +#define RB_PARENT_ROTATE_LEFT(parent, left, tmp, field) do {           \
> ...
> 2.26.2
>
>