git: 2120d7f57aa0 - main - rb_tree: fine-tune rebalancing code
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Date: Mon, 04 Jul 2022 17:32:55 UTC
The branch main has been updated by dougm:
URL: https://cgit.FreeBSD.org/src/commit/?id=2120d7f57aa0ee48d0be7a4309072bb332d568dd
commit 2120d7f57aa0ee48d0be7a4309072bb332d568dd
Author: Doug Moore <dougm@FreeBSD.org>
AuthorDate: 2022-07-04 17:28:35 +0000
Commit: Doug Moore <dougm@FreeBSD.org>
CommitDate: 2022-07-04 17:28:35 +0000
rb_tree: fine-tune rebalancing code
Change parts of RB_INSERT_COLOR and RB_REMOVE_COLOR to reduce the
number of operations, by, in some cases, flipping two color bits at a
time instead of flipping each individually, in separate operations,
and by using a switch statement to replace a sequence of if-elses.
Rewrite RB_SET_PARENT to generate fewer instructions. These changes
reduce the code size by over 100 bytes on some architectures.
Also, allow RB users to define a preprocessor symbol to generate
RB_REMOVE_COLOR code that matches the implementation described in the
original weak-AVL paper in one particular case, instead of the still
correct, but slightly more efficient implementation of that case
currently implemented.
Reviewed by: alc
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D35524
---
sys/sys/tree.h | 104 +++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 71 insertions(+), 33 deletions(-)
diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index 553d84e57cc8..3f48c07a70b1 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -340,6 +340,7 @@ struct { \
#define RB_RED_MASK ((__uintptr_t)3)
#define RB_FLIP_LEFT(elm, field) (RB_BITS(elm, field) ^= RB_RED_L)
#define RB_FLIP_RIGHT(elm, field) (RB_BITS(elm, field) ^= RB_RED_R)
+#define RB_FLIP_ALL(elm, field) (RB_BITS(elm, field) ^= RB_RED_MASK)
#define RB_RED_LEFT(elm, field) ((RB_BITS(elm, field) & RB_RED_L) != 0)
#define RB_RED_RIGHT(elm, field) ((RB_BITS(elm, field) & RB_RED_R) != 0)
#define RB_PARENT(elm, field) ((__typeof(RB_UP(elm, field))) \
@@ -348,8 +349,8 @@ struct { \
#define RB_EMPTY(head) (RB_ROOT(head) == NULL)
#define RB_SET_PARENT(dst, src, field) do { \
- RB_BITS(dst, field) &= RB_RED_MASK; \
- RB_BITS(dst, field) |= (__uintptr_t)src; \
+ RB_BITS(dst, field) = (__uintptr_t)src | \
+ (RB_BITS(dst, field) & RB_RED_MASK); \
} while (/*CONSTCOND*/ 0)
#define RB_SET(elm, parent, field) do { \
@@ -487,13 +488,14 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
continue; \
} \
if (!RB_RED_RIGHT(elm, field)) { \
- RB_FLIP_LEFT(elm, field); \
/* coverity[uninit_use] */ \
RB_ROTATE_LEFT(head, elm, child, field);\
- if (RB_RED_LEFT(child, field)) \
- RB_FLIP_RIGHT(elm, field); \
- else if (RB_RED_RIGHT(child, field)) \
+ if (RB_RED_RIGHT(child, field)) \
RB_FLIP_LEFT(parent, field); \
+ if (RB_RED_LEFT(child, field)) \
+ RB_FLIP_ALL(elm, field); \
+ else \
+ RB_FLIP_LEFT(elm, field); \
elm = child; \
} \
RB_ROTATE_RIGHT(head, parent, elm, field); \
@@ -509,13 +511,14 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
continue; \
} \
if (!RB_RED_LEFT(elm, field)) { \
- RB_FLIP_RIGHT(elm, field); \
/* coverity[uninit_use] */ \
RB_ROTATE_RIGHT(head, elm, child, field);\
- if (RB_RED_RIGHT(child, field)) \
- RB_FLIP_LEFT(elm, field); \
- else if (RB_RED_LEFT(child, field)) \
+ if (RB_RED_LEFT(child, field)) \
RB_FLIP_RIGHT(parent, field); \
+ if (RB_RED_RIGHT(child, field)) \
+ RB_FLIP_ALL(elm, field); \
+ else \
+ RB_FLIP_RIGHT(elm, field); \
elm = child; \
} \
RB_ROTATE_LEFT(head, parent, elm, field); \
@@ -525,6 +528,17 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
} \
}
+#ifndef RB_STRICT_HST
+/*
+ * In REMOVE_COLOR, the HST paper, in figure 3, in the single-rotate case, has
+ * 'parent' with one higher rank, and then reduces its rank if 'parent' has
+ * become a leaf. This implementation always has the parent in its new position
+ * with lower rank, to avoid the leaf check. Define RB_STRICT_HST to 1 to get
+ * the behavior that HST describes.
+ */
+#define RB_STRICT_HST 0
+#endif
+
#define RB_GENERATE_REMOVE_COLOR(name, type, field, attr) \
attr void \
name##_RB_REMOVE_COLOR(struct name *head, \
@@ -539,7 +553,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
if (parent == NULL) \
return; \
} \
- do { \
+ do { \
if (RB_LEFT(parent, field) == elm) { \
if (!RB_RED_LEFT(parent, field)) { \
RB_FLIP_LEFT(parent, field); \
@@ -551,24 +565,36 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
} \
sib = RB_RIGHT(parent, field); \
- if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
- RB_BITS(sib, field) &= ~RB_RED_MASK; \
+ switch (RB_BITS(sib, field) & RB_RED_MASK) { \
+ case RB_RED_MASK: \
+ RB_FLIP_ALL(sib, field); \
elm = parent; \
continue; \
- } \
- RB_FLIP_RIGHT(sib, field); \
- if (RB_RED_LEFT(sib, field)) \
- RB_FLIP_LEFT(parent, field); \
- else if (!RB_RED_RIGHT(sib, field)) { \
- RB_FLIP_LEFT(parent, field); \
+ case RB_RED_R: \
elm = RB_LEFT(sib, field); \
RB_ROTATE_RIGHT(head, sib, elm, field); \
- if (RB_RED_RIGHT(elm, field)) \
- RB_FLIP_LEFT(sib, field); \
if (RB_RED_LEFT(elm, field)) \
- RB_FLIP_RIGHT(parent, field); \
+ RB_FLIP_ALL(parent, field); \
+ else \
+ RB_FLIP_LEFT(parent, field); \
+ if (RB_RED_RIGHT(elm, field)) \
+ RB_FLIP_ALL(sib, field); \
+ else \
+ RB_FLIP_RIGHT(sib, field); \
RB_BITS(elm, field) |= RB_RED_MASK; \
sib = elm; \
+ break; \
+ case RB_RED_L: \
+ if (RB_STRICT_HST && elm != NULL) { \
+ RB_FLIP_RIGHT(parent, field); \
+ RB_FLIP_ALL(sib, field); \
+ break; \
+ } \
+ RB_FLIP_LEFT(parent, field); \
+ /* FALLTHROUGH */ \
+ default: \
+ RB_FLIP_RIGHT(sib, field); \
+ break; \
} \
RB_ROTATE_LEFT(head, parent, sib, field); \
} else { \
@@ -582,24 +608,36 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
} \
sib = RB_LEFT(parent, field); \
- if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
- RB_BITS(sib, field) &= ~RB_RED_MASK; \
+ switch (RB_BITS(sib, field) & RB_RED_MASK) { \
+ case RB_RED_MASK: \
+ RB_FLIP_ALL(sib, field); \
elm = parent; \
continue; \
- } \
- RB_FLIP_LEFT(sib, field); \
- if (RB_RED_RIGHT(sib, field)) \
- RB_FLIP_RIGHT(parent, field); \
- else if (!RB_RED_LEFT(sib, field)) { \
- RB_FLIP_RIGHT(parent, field); \
+ case RB_RED_L: \
elm = RB_RIGHT(sib, field); \
RB_ROTATE_LEFT(head, sib, elm, field); \
- if (RB_RED_LEFT(elm, field)) \
- RB_FLIP_RIGHT(sib, field); \
if (RB_RED_RIGHT(elm, field)) \
- RB_FLIP_LEFT(parent, field); \
+ RB_FLIP_ALL(parent, field); \
+ else \
+ RB_FLIP_RIGHT(parent, field); \
+ if (RB_RED_LEFT(elm, field)) \
+ RB_FLIP_ALL(sib, field); \
+ else \
+ RB_FLIP_LEFT(sib, field); \
RB_BITS(elm, field) |= RB_RED_MASK; \
sib = elm; \
+ break; \
+ case RB_RED_R: \
+ if (RB_STRICT_HST && elm != NULL) { \
+ RB_FLIP_LEFT(parent, field); \
+ RB_FLIP_ALL(sib, field); \
+ break; \
+ } \
+ RB_FLIP_RIGHT(parent, field); \
+ /* FALLTHROUGH */ \
+ default: \
+ RB_FLIP_LEFT(sib, field); \
+ break; \
} \
RB_ROTATE_RIGHT(head, parent, sib, field); \
} \