test-mergesort: use DEFINE_LIST_SORT

Build a typed sort function for the mergesort performance test tool
using DEFINE_LIST_SORT instead of calling llist_mergesort().  This gets
rid of the next pointer accessor functions and improves the performance
at the cost of a slightly higher object text size.

Before:
0071.12: llist_mergesort() unsorted    0.24(0.22+0.01)
0071.14: llist_mergesort() sorted      0.12(0.10+0.01)
0071.16: llist_mergesort() reversed    0.12(0.10+0.01)

__TEXT	__DATA	__OBJC	others	dec	hex
6407	276	0	24701	31384	7a98	t/helper/test-mergesort.o

With this patch:
0071.12: DEFINE_LIST_SORT unsorted     0.22(0.21+0.01)
0071.14: DEFINE_LIST_SORT sorted       0.11(0.10+0.01)
0071.16: DEFINE_LIST_SORT reversed     0.11(0.10+0.01)

__TEXT	__DATA	__OBJC	others	dec	hex
6615	276	0	25832	32723	7fd3	t/helper/test-mergesort.o

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

t/helper/test-mergesort.c

@@ -13,19 +13,10 @@ struct line {
 	struct line *next;
 };
 
-static void *get_next(const void *a)
-{
-	return ((const struct line *)a)->next;
-}
-
-static void set_next(void *a, void *b)
-{
-	((struct line *)a)->next = b;
-}
+DEFINE_LIST_SORT(static, sort_lines, struct line, next);
 
-static int compare_strings(const void *a, const void *b)
+static int compare_strings(const struct line *x, const struct line *y)
 {
-	const struct line *x = a, *y = b;
 	return strcmp(x->text, y->text);
 }
 
@@ -47,7 +38,7 @@ static int sort_stdin(void)
 		p = line;
 	}
 
-	lines = llist_mergesort(lines, get_next, set_next, compare_strings);
+	sort_lines(&lines, compare_strings);
 
 	while (lines) {
 		puts(lines->text);

t/perf/p0071-sort.sh

@@ -40,11 +40,11 @@ done
 
 for file in unsorted sorted reversed
 do
-	test_perf "llist_mergesort() $file" "
+	test_perf "DEFINE_LIST_SORT $file" "
 		test-tool mergesort sort <$file >actual
 	"
 
-	test_expect_success "llist_mergesort() $file sorts like sort(1)" "
+	test_expect_success "DEFINE_LIST_SORT $file sorts like sort(1)" "
 		test_cmp_bin sorted actual
 	"
 done