From 3d5a6d38e65ad9e214901da901310a05f7a37a29 Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Wed, 14 Apr 2021 18:50:50 +0200
Subject: [PATCH] Avoid calling size() in empty() member functions

Might slightly improve the speed of applications built in Debug mode.

Having `empty()` call `size()` is somewhat disappointing for users who follow the guideline to replace their `size()` calls by the corresponding `empty()` calls. For example by Clang-Tidy:
https://clang.llvm.org/extra/clang-tidy/checks/readability-container-size-empty.html
---
 stl/inc/vector  | 2 +-
 stl/inc/xstring | 2 +-
 stl/inc/xtree   | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/stl/inc/vector b/stl/inc/vector
index 9a943420d43..52fef59fc25 100644
--- a/stl/inc/vector
+++ b/stl/inc/vector
@@ -2798,7 +2798,7 @@ public:
     }
 
     _NODISCARD _CONSTEXPR20_CONTAINER bool empty() const noexcept {
-        return size() == 0;
+        return this->_Mysize == 0;
     }
 
     _NODISCARD _CONSTEXPR20_CONTAINER allocator_type get_allocator() const noexcept {
diff --git a/stl/inc/xstring b/stl/inc/xstring
index 9e63cab02b2..36cef22456a 100644
--- a/stl/inc/xstring
+++ b/stl/inc/xstring
@@ -4016,7 +4016,7 @@ public:
 #endif // _HAS_CXX20
 
     _NODISCARD _CONSTEXPR20_CONTAINER bool empty() const noexcept {
-        return size() == 0;
+        return _Mypair._Myval2._Mysize == 0;
     }
 
     _CONSTEXPR20_CONTAINER size_type copy(
diff --git a/stl/inc/xtree b/stl/inc/xtree
index 3d9e6786ee0..12b8d6c7e79 100644
--- a/stl/inc/xtree
+++ b/stl/inc/xtree
@@ -1216,7 +1216,7 @@ public:
     }
 
     _NODISCARD bool empty() const noexcept {
-        return size() == 0;
+        return _Get_scary()->_Mysize == 0;
     }
 
     _NODISCARD allocator_type get_allocator() const noexcept {