--- /dev/null
+++ libmalloc/libmalloc-374.40.6/tests/perf_realloc.c
@@ -0,0 +1,160 @@
+#include <stdlib.h>
+#include <mach/vm_page_size.h>
+#include <../src/internal.h>
+#include <darwintest.h>
+#include <perfcheck_keys.h>
+
+#pragma mark -
+#pragma mark Helper code
+
+#define PAGE_SPREAD 8
+#define MAX_NAME_SIZE 256
+#define OUTLIER_TIME 20000
+
+// This value is a guess that will be refined over time.
+#define PERFCHECK_THRESHOLD_PCT	10.0
+
+static char name[MAX_NAME_SIZE];
+#define NUMBER_OF_SAMPLES_FOR_BATCH(s) _dt_stat_batch_size((dt_stat_t)s)
+
+// Measures the time required to realloc a block of memory of given size
+// by a specified amount.
+static void
+realloc_by_amount(const char *base_metric_name, size_t size, ssize_t amount,
+		bool amount_is_random)
+{
+	if (amount_is_random) {
+		snprintf(name, MAX_NAME_SIZE, amount >= 0 ?
+			 "%s_from_%llu_up_random" : "%s_from_%llu_down_random",
+			 base_metric_name, (uint64_t)size);
+	} else {
+		snprintf(name, MAX_NAME_SIZE, amount >= 0 ?
+				 "%s_from_%llu_up_%ld" : "%s_from_%llu_down_%ld",
+				 base_metric_name, (uint64_t)size, labs(amount));
+	}
+
+	uint64_t total_time = 0;
+	int count = 0;
+	dt_stat_time_t s = dt_stat_time_create(name);
+	dt_stat_set_variable((dt_stat_t)s, "size (bytes)", (unsigned int)size);
+	dt_stat_set_variable((dt_stat_t)s, "amount (bytes)", (int)amount);
+	dt_stat_token now = dt_stat_time_begin(s);
+
+	for (;;) {
+		void *ptr = malloc(size);
+		T_QUIET; T_ASSERT_NOTNULL(ptr, "malloc for size %llu failed", (uint64_t)size);
+
+		dt_stat_token start = dt_stat_time_begin(s);
+		ptr = realloc(ptr, size + amount);
+		dt_stat_token end = dt_stat_time_begin(s);
+		T_QUIET; T_ASSERT_NOTNULL(ptr,
+				"realloc from size %llu to size %llu failed", (uint64_t)size,
+				(uint64_t)(size + amount));
+		total_time += end - start;
+		free(ptr);
+
+		if (++count >= NUMBER_OF_SAMPLES_FOR_BATCH(s)) {
+			// Discard outliers or the test won't converge -- this should
+			// be done in libdarwintest
+			if (total_time/count < OUTLIER_TIME) {
+				dt_stat_mach_time_add_batch(s, count, total_time);
+			}
+			total_time = 0;
+			count = 0;
+			if (dt_stat_stable(s)) {
+				break;
+			}
+		}
+	}
+
+	dt_stat_finalize(s);
+}
+
+// Times a set of size adjustments from a given base.
+static void
+realloc_test_set(const char *base_name, size_t start_size)
+{
+	ssize_t adj = 1;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -adj, false);
+
+	adj = 8;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -adj, false);
+
+	adj = 16;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -adj, false);
+
+#if INCLUDE_RANDOM_SIZE_TESTS
+	adj = 1 + arc4random_uniform(vm_page_size - 1);
+	realloc_by_amount(base_name, start_size, adj, true);
+	realloc_by_amount(base_name, start_size + adj, -adj, true);
+
+	uint32_t pages = 1 + arc4random_uniform(PAGE_SPREAD);
+	adj = pages * vm_page_size;
+	realloc_by_amount(base_name, start_size, adj, true);
+	realloc_by_amount(base_name, start_size + adj, -adj, true);
+#else // INCLUDE_RANDOM_SIZE_TESTS
+	T_LOG("Skipping random size tests");
+#endif // INCLUDE_RANDOM_SIZE_TESTS
+
+	adj = vm_page_size;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -adj, false);
+
+	adj = 4 * vm_page_size;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -adj, false);
+
+	// Adjust up and then down by over half the size of the allocation --
+	// this skips the fast path in some allocators.
+	adj = 4 * vm_page_size;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -(((ssize_t)start_size) + adj)/2 - 1, false);
+
+	adj = 32;
+	realloc_by_amount(base_name, start_size, adj, false);
+	realloc_by_amount(base_name, start_size + adj, -(((ssize_t)start_size) + adj)/2 - 1, false);
+}
+
+static void
+realloc_tests(const char *base_name, boolean_t using_nano)
+{
+	// tiny or nano
+	realloc_test_set(using_nano ? base_name : "Tiny", 8);
+
+	if (!using_nano) {
+		// No point in running these tests three times.
+
+		// tiny
+		realloc_test_set("Tiny", 512);
+
+		// small
+		realloc_test_set("Small", 2048);
+
+		// large
+		realloc_test_set("Large", 128 * 1024);
+	}
+
+	T_END;
+}
+
+#pragma mark -
+#pragma mark Tests for realloc()
+
+T_DECL(realloc_perf_base, "realloc without nano",
+	   T_META_TAG_PERF, T_META_ENVVAR("MallocNanoZone=0"))
+{
+	realloc_tests("NoNano", false);
+}
+
+T_DECL(realloc_perf_nanov2, "realloc with nanoV2",
+	   T_META_TAG_PERF, T_META_ENVVAR("MallocNanoZone=V2"))
+{
+#if CONFIG_NANOZONE
+	realloc_tests("Nanov2", true);
+#else // CONFIG_NANOZONE
+	T_SKIP("Nano allocator not configured");
+#endif // CONFIG_NANOZONE
+}