Use TEST_MAYBE_UNUSED, separately count allocations and deallocations

Author: frederick-vs-ja

libcxx/test/std/strings/basic.string/string.capacity/deallocate_size.pass.cpp

@@ -18,7 +18,8 @@
 
 #include "test_macros.h"
 
-static std::ptrdiff_t allocated_;
+static std::size_t allocated_;
+static std::size_t deallocated_;
 
 template <class T, class Sz>
 struct test_alloc {
@@ -41,12 +42,12 @@ struct test_alloc {
   TEST_CONSTEXPR test_alloc(const test_alloc<U, Sz>&) TEST_NOEXCEPT {}
 
   pointer allocate(size_type n, const void* = nullptr) {
-    allocated_ += static_cast<std::ptrdiff_t>(n);
+    allocated_ += static_cast<std::size_t>(n);
     return std::allocator<value_type>().allocate(static_cast<std::size_t>(n));
   }
 
   void deallocate(pointer p, size_type s) {
-    allocated_ -= static_cast<std::ptrdiff_t>(s);
+    deallocated_ += static_cast<std::size_t>(s);
     std::allocator<value_type>().deallocate(p, static_cast<std::size_t>(s));
   }
 
@@ -65,13 +66,11 @@ struct test_alloc {
 
 template <class Sz>
 void test() {
-  using Str = std::basic_string<char, std::char_traits<char>, test_alloc<char, Sz> >;
   for (int i = 1; i < 1000; ++i) {
     {
-      Str s(i, 't');
-      (void)s;
+      TEST_MAYBE_UNUSED std::basic_string<char, std::char_traits<char>, test_alloc<char, Sz> > s(i, 't');
     }
-    assert(allocated_ == 0);
+    assert(allocated_ == deallocated_);
   }
 }