maple_tree: mtree_range_walk() clean up

mtree_range_walk() needed to be updated to avoid checking if there was a
pivot value.  On closer examination, the code could avoid setting min or
max in certain scenarios.  The commit removes the extra check for
pivot[offset] before setting max and only sets max when necessary.  It
also only sets min if it is necessary by checking offset 0 prior to the
loop (as it has always done).

The commit also drops a dead node check since the end of the node will
return the array size when the last slot is occupied (by a potential reuse
in a dead node).  The data will be discarded later if the node is marked
dead.

Benchmarking these changes results in an increase in performance of 5.45%
using the BENCH_WALK in the maple tree test code.

Link: https://lkml.kernel.org/r/20231101171629.3612299-13-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -2806,32 +2806,29 @@ static inline void *mtree_range_walk(struct ma_state *mas)
 	min = mas->min;
 	max = mas->max;
 	do {
-		offset = 0;
 		last = next;
 		node = mte_to_node(next);
 		type = mte_node_type(next);
 		pivots = ma_pivots(node, type);
 		end = ma_data_end(node, type, pivots, max);
-		if (unlikely(ma_dead_node(node)))
-			goto dead_node;
-
-		if (pivots[offset] >= mas->index) {
-			prev_max = max;
 		prev_min = min;
-			max = pivots[offset];
+		prev_max = max;
+		if (pivots[0] >= mas->index) {
+			offset = 0;
+			max = pivots[0];
 			goto next;
 		}
 
-		do {
+		offset = 1;
+		while (offset < end) {
+			if (pivots[offset] >= mas->index) {
+				max = pivots[offset];
+				break;
+			}
 			offset++;
-		} while ((offset < end) && (pivots[offset] < mas->index));
+		}
 
-		prev_min = min;
 		min = pivots[offset - 1] + 1;
-		prev_max = max;
-		if (likely(offset < end && pivots[offset]))
-			max = pivots[offset];
-
 next:
 		slots = ma_slots(node, type);
 		next = mt_slot(mas->tree, slots, offset);