linux-kernel - [PATCH v1] lib/rbtree: Use '+' instead of '|' for setting color.

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Date:   Tue,  4 Apr 2023 17:13:51 -0500
From:   Noah Goldstein <goldstein.w.n@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     goldstein.w.n@...il.com, walken@...gle.com,
        akpm@...ux-foundation.org
Subject: [PATCH v1] lib/rbtree: Use '+' instead of '|' for setting color.

This has a slight benefit for x86 and has no effect on other targets.

The benefit to x86 is it change the codegen for setting a node to
block from `mov %r0, %r1; or $RB_BLACK, %r1` to `lea RB_BLACK(%r0),
%r1` which saves an instructions.

In all other cases it just replace ALU with ALU (or -> and) which
perform the same on all machines I am aware of.

Total instructions in rbtree.o:
    Before  - 802
    After   - 782

so it saves about 20 `mov` instructions.

Signed-off-by: Noah Goldstein <goldstein.w.n@...il.com>
---
 include/linux/rbtree_augmented.h | 4 ++--
 lib/rbtree.c                     | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
index d1c53e9d8c75..7ee7ed5de722 100644
--- a/include/linux/rbtree_augmented.h
+++ b/include/linux/rbtree_augmented.h
@@ -156,13 +156,13 @@ RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,					      \
 
 static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
 {
-	rb->__rb_parent_color = rb_color(rb) | (unsigned long)p;
+	rb->__rb_parent_color = rb_color(rb) + (unsigned long)p;
 }
 
 static inline void rb_set_parent_color(struct rb_node *rb,
 				       struct rb_node *p, int color)
 {
-	rb->__rb_parent_color = (unsigned long)p | color;
+	rb->__rb_parent_color = (unsigned long)p + color;
 }
 
 static inline void
diff --git a/lib/rbtree.c b/lib/rbtree.c
index c4ac5c2421f2..5114eda6309c 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -58,7 +58,7 @@
 
 static inline void rb_set_black(struct rb_node *rb)
 {
-	rb->__rb_parent_color |= RB_BLACK;
+	rb->__rb_parent_color += RB_BLACK;
 }
 
 static inline struct rb_node *rb_red_parent(struct rb_node *red)
-- 
2.34.1