Avoid calling size() in empty() member functions (#1836)

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 {

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(

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 {