[PATCH 2/4] maple_tree: use mt_pivot_count() to replace mt_slot_count() - 1

[Wei Yang <richard.weiyang@gmail.com>]

We have (mt_slot_count() - 1 == mt_pivot_count()), except for
maple_dense node. Since mas_mab_cp() doesn't apply to maple_dense node,
it is fine to use mt_pivot_count() here.

By doing so we can save instruction to decrease 1 from mt_slot_count().
Below is the comparison of generated code.

Current:

.L1595:
  lib/maple_tree.c:3165: 		mas_mab_cp(mas, split + skip, mt_slot_count(mas->node) - 1,
	movl	%ebx, (%esp)	# prephitmp_234,
	movzbl	mt_slots(%edx), %ecx	# mt_slots[_90], mt_slots[_90]
	movl	%esi, 4(%esp)	# _26,
	movzbl	-23(%ebp), %eax	# %sfp,
	movzbl	-21(%ebp), %edx	# %sfp, split
	decb	%cl	# tmp258
	movzbl	%cl, %ecx	# tmp258, tmp260
	addb	%al, %dl	#, split
	movl	-16(%ebp), %eax	# %sfp,
	movzbl	%dl, %edx	# tmp261, tmp262
	call	mas_mab_cp	#

After applying this patch:

.L1595:
  lib/maple_tree.c:3165: 		mas_mab_cp(mas, split + skip, mt_pivot_count(mas->node),
	movl	%ebx, (%esp)	# prephitmp_231,
	movzbl	mt_pivots(%edx), %ecx	# mt_pivots[_87], mt_pivots[_87]
	movl	%esi, 4(%esp)	# _26,
	movzbl	-23(%ebp), %eax	# %sfp,
	movzbl	-21(%ebp), %edx	# %sfp, split
	addb	%al, %dl	#, split
	movl	-16(%ebp), %eax	# %sfp,
	movzbl	%dl, %edx	# tmp256, tmp257
	call	mas_mab_cp	#

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 lib/maple_tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 51f49b29b8b0..8ff075645f21 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3167,7 +3167,7 @@ static inline void mast_fill_bnode(struct maple_subtree_state *mast,
 		cp = false;
 
 	if (cp)
-		mas_mab_cp(mas, split + skip, mt_slot_count(mas->node) - 1,
+		mas_mab_cp(mas, split + skip, mt_pivot_count(mas->node),
 			   mast->bn, mast->bn->b_end);
 
 	mast->bn->b_end--;
-- 
2.34.1