[ASan][libc++] Optimize __annotate_delete for the default allocator

This commit optimizes the ASan helper functions `__annotate_delete()`, in `std::basic_string`, `std::vector` and `std::deque`, by adding `if` statements to prevent unpoisoning of memory for the default allocator. Unpoisoning is not required by the default allocator, and since it is widely used, this optimization should yield a meaningful performance improvement.

The optimization was suggested by @EricWF.

Author: Advenam Tacet

libcxx/include/deque

@@ -1011,6 +1011,9 @@ private:
 
   _LIBCPP_HIDE_FROM_ABI void __annotate_delete() const _NOEXCEPT {
 #ifndef _LIBCPP_HAS_NO_ASAN
+    // The default allocator does not require unpoisoning before returning memory.
+    if _LIBCPP_CONSTEXPR (is_same<allocator_type, allocator<_Tp>>::value)
+      return;
     if (empty()) {
       for (size_t __i = 0; __i < __map_.size(); ++__i) {
         __annotate_whole_block(__i, __asan_unposion);

libcxx/include/string

@@ -1912,8 +1912,10 @@ private:
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __annotate_delete() const _NOEXCEPT {
 #if !defined(_LIBCPP_HAS_NO_ASAN) && defined(_LIBCPP_INSTRUMENTED_WITH_ASAN)
-    if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
-      __annotate_contiguous_container(data() + size() + 1, data() + capacity() + 1);
+    // The default allocator does not require unpoisoning before returning memory.
+    if _LIBCPP_CONSTEXPR (!is_same<allocator_type, allocator<__default_allocator_type>>::value)
+      if (!__libcpp_is_constant_evaluated() && (__asan_short_string_is_annotated() || __is_long()))
+        __annotate_contiguous_container(data() + size() + 1, data() + capacity() + 1);
 #endif
   }
 

libcxx/include/vector

@@ -853,7 +853,9 @@ private:
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __annotate_delete() const _NOEXCEPT {
 #ifndef _LIBCPP_HAS_NO_ASAN
-    __annotate_contiguous_container(data(), data() + capacity(), data() + size(), data() + capacity());
+    // The default allocator does not require unpoisoning before returning memory.
+    if _LIBCPP_CONSTEXPR (!is_same<allocator_type, __default_allocator_type>::value)
+      __annotate_contiguous_container(data(), data() + capacity(), data() + size(), data() + capacity());
 #endif
   }