Realloc: Make behavior of realloc(ptr, 0) configurable.

test/unit/zero_realloc_free.c

@@ -0,0 +1,33 @@
+#include "test/jemalloc_test.h"
+
+static uint64_t
+deallocated() {
+	if (!config_stats) {
+		return 0;
+	}
+	uint64_t deallocated;
+	size_t sz = sizeof(deallocated);
+	assert_d_eq(mallctl("thread.deallocated", (void *)&deallocated, &sz,
+	    NULL, 0), 0, "Unexpected mallctl failure");
+	return deallocated;
+}
+
+TEST_BEGIN(test_realloc_free) {
+	void *ptr = mallocx(42, 0);
+	assert_ptr_not_null(ptr, "Unexpected mallocx error");
+	uint64_t deallocated_before = deallocated();
+	ptr = realloc(ptr, 0);
+	uint64_t deallocated_after = deallocated();
+	assert_ptr_null(ptr, "Realloc didn't free");
+	if (config_stats) {
+		assert_u64_gt(deallocated_after, deallocated_before,
+		    "Realloc didn't free");
+	}
+}
+TEST_END
+
+int
+main(void) {
+	return test(
+	    test_realloc_free);
+}