diff --git a/libcxx/test/support/constexpr_char_traits.h b/libcxx/test/support/constexpr_char_traits.h
--- a/libcxx/test/support/constexpr_char_traits.h
+++ b/libcxx/test/support/constexpr_char_traits.h
@@ -15,10 +15,10 @@
 
 #include "test_macros.h"
 
-template <class _CharT>
+template <class CharT>
 struct constexpr_char_traits
 {
-    typedef _CharT    char_type;
+    typedef CharT     char_type;
     typedef int       int_type;
     typedef std::streamoff off_type;
     typedef std::streampos pos_type;
@@ -26,116 +26,116 @@
     // The comparison_category is omitted so the class will have weak_ordering
     // in C++20. This is intentional.
 
-    static TEST_CONSTEXPR_CXX14 void assign(char_type& __c1, const char_type& __c2) TEST_NOEXCEPT
-        {__c1 = __c2;}
+    static TEST_CONSTEXPR_CXX14 void assign(char_type& c1, const char_type& c2) TEST_NOEXCEPT
+        {c1 = c2;}
 
-    static TEST_CONSTEXPR bool eq(char_type __c1, char_type __c2) TEST_NOEXCEPT
-        {return __c1 == __c2;}
+    static TEST_CONSTEXPR bool eq(char_type c1, char_type c2) TEST_NOEXCEPT
+        {return c1 == c2;}
 
-    static TEST_CONSTEXPR  bool lt(char_type __c1, char_type __c2) TEST_NOEXCEPT
-        {return __c1 < __c2;}
+    static TEST_CONSTEXPR  bool lt(char_type c1, char_type c2) TEST_NOEXCEPT
+        {return c1 < c2;}
 
-    static TEST_CONSTEXPR_CXX14 int              compare(const char_type* __s1, const char_type* __s2, size_t __n);
-    static TEST_CONSTEXPR_CXX14 size_t           length(const char_type* __s);
-    static TEST_CONSTEXPR_CXX14 const char_type* find(const char_type* __s, size_t __n, const char_type& __a);
-    static TEST_CONSTEXPR_CXX14 char_type*       move(char_type* __s1, const char_type* __s2, size_t __n);
-    static TEST_CONSTEXPR_CXX14 char_type*       copy(char_type* __s1, const char_type* __s2, size_t __n);
-    static TEST_CONSTEXPR_CXX14 char_type*       assign(char_type* __s, size_t __n, char_type __a);
+    static TEST_CONSTEXPR_CXX14 int              compare(const char_type* s1, const char_type* s2, size_t n);
+    static TEST_CONSTEXPR_CXX14 size_t           length(const char_type* s);
+    static TEST_CONSTEXPR_CXX14 const char_type* find(const char_type* s, size_t n, const char_type& a);
+    static TEST_CONSTEXPR_CXX14 char_type*       move(char_type* s1, const char_type* s2, size_t n);
+    static TEST_CONSTEXPR_CXX14 char_type*       copy(char_type* s1, const char_type* s2, size_t n);
+    static TEST_CONSTEXPR_CXX14 char_type*       assign(char_type* s, size_t n, char_type a);
 
-    static TEST_CONSTEXPR int_type  not_eof(int_type __c) TEST_NOEXCEPT
-        {return eq_int_type(__c, eof()) ? ~eof() : __c;}
+    static TEST_CONSTEXPR int_type  not_eof(int_type c) TEST_NOEXCEPT
+        {return eq_int_type(c, eof()) ? ~eof() : c;}
 
-    static TEST_CONSTEXPR char_type to_char_type(int_type __c) TEST_NOEXCEPT
-        {return char_type(__c);}
+    static TEST_CONSTEXPR char_type to_char_type(int_type c) TEST_NOEXCEPT
+        {return char_type(c);}
 
-    static TEST_CONSTEXPR int_type  to_int_type(char_type __c) TEST_NOEXCEPT
-        {return int_type(__c);}
+    static TEST_CONSTEXPR int_type  to_int_type(char_type c) TEST_NOEXCEPT
+        {return int_type(c);}
 
-    static TEST_CONSTEXPR bool      eq_int_type(int_type __c1, int_type __c2) TEST_NOEXCEPT
-        {return __c1 == __c2;}
+    static TEST_CONSTEXPR bool      eq_int_type(int_type c1, int_type c2) TEST_NOEXCEPT
+        {return c1 == c2;}
 
     static TEST_CONSTEXPR int_type  eof() TEST_NOEXCEPT
         {return int_type(EOF);}
 };
 
 
-template <class _CharT>
+template <class CharT>
 TEST_CONSTEXPR_CXX14 int
-constexpr_char_traits<_CharT>::compare(const char_type* __s1, const char_type* __s2, size_t __n)
+constexpr_char_traits<CharT>::compare(const char_type* s1, const char_type* s2, size_t n)
 {
-    for (; __n; --__n, ++__s1, ++__s2)
+    for (; n; --n, ++s1, ++s2)
     {
-        if (lt(*__s1, *__s2))
+        if (lt(*s1, *s2))
             return -1;
-        if (lt(*__s2, *__s1))
+        if (lt(*s2, *s1))
             return 1;
     }
     return 0;
 }
 
-template <class _CharT>
+template <class CharT>
 TEST_CONSTEXPR_CXX14 size_t
-constexpr_char_traits<_CharT>::length(const char_type* __s)
+constexpr_char_traits<CharT>::length(const char_type* s)
 {
-    size_t __len = 0;
-    for (; !eq(*__s, char_type(0)); ++__s)
-        ++__len;
-    return __len;
+    size_t len = 0;
+    for (; !eq(*s, char_type(0)); ++s)
+        ++len;
+    return len;
 }
 
-template <class _CharT>
-TEST_CONSTEXPR_CXX14 const _CharT*
-constexpr_char_traits<_CharT>::find(const char_type* __s, size_t __n, const char_type& __a)
+template <class CharT>
+TEST_CONSTEXPR_CXX14 const CharT*
+constexpr_char_traits<CharT>::find(const char_type* s, size_t n, const char_type& a)
 {
-    for (; __n; --__n)
+    for (; n; --n)
     {
-        if (eq(*__s, __a))
-            return __s;
-        ++__s;
+        if (eq(*s, a))
+            return s;
+        ++s;
     }
     return 0;
 }
 
-template <class _CharT>
-TEST_CONSTEXPR_CXX14 _CharT*
-constexpr_char_traits<_CharT>::move(char_type* __s1, const char_type* __s2, size_t __n)
+template <class CharT>
+TEST_CONSTEXPR_CXX14 CharT*
+constexpr_char_traits<CharT>::move(char_type* s1, const char_type* s2, size_t n)
 {
-    char_type* __r = __s1;
-    if (__s1 < __s2)
+    char_type* r = s1;
+    if (s1 < s2)
     {
-        for (; __n; --__n, ++__s1, ++__s2)
-            assign(*__s1, *__s2);
+        for (; n; --n, ++s1, ++s2)
+            assign(*s1, *s2);
     }
-    else if (__s2 < __s1)
+    else if (s2 < s1)
     {
-        __s1 += __n;
-        __s2 += __n;
-        for (; __n; --__n)
-            assign(*--__s1, *--__s2);
+        s1 += n;
+        s2 += n;
+        for (; n; --n)
+            assign(*--s1, *--s2);
     }
-    return __r;
+    return r;
 }
 
-template <class _CharT>
-TEST_CONSTEXPR_CXX14 _CharT*
-constexpr_char_traits<_CharT>::copy(char_type* __s1, const char_type* __s2, size_t __n)
+template <class CharT>
+TEST_CONSTEXPR_CXX14 CharT*
+constexpr_char_traits<CharT>::copy(char_type* s1, const char_type* s2, size_t n)
 {
     if (!TEST_IS_CONSTANT_EVALUATED) // fails in constexpr because we might be comparing unrelated pointers
-        assert(__s2 < __s1 || __s2 >= __s1+__n);
-    char_type* __r = __s1;
-    for (; __n; --__n, ++__s1, ++__s2)
-        assign(*__s1, *__s2);
-    return __r;
+        assert(s2 < s1 || s2 >= s1+n);
+    char_type* r = s1;
+    for (; n; --n, ++s1, ++s2)
+        assign(*s1, *s2);
+    return r;
 }
 
-template <class _CharT>
-TEST_CONSTEXPR_CXX14 _CharT*
-constexpr_char_traits<_CharT>::assign(char_type* __s, size_t __n, char_type __a)
+template <class CharT>
+TEST_CONSTEXPR_CXX14 CharT*
+constexpr_char_traits<CharT>::assign(char_type* s, size_t n, char_type a)
 {
-    char_type* __r = __s;
-    for (; __n; --__n, ++__s)
-        assign(*__s, __a);
-    return __r;
+    char_type* r = s;
+    for (; n; --n, ++s)
+        assign(*s, a);
+    return r;
 }
 
 #endif // _CONSTEXPR_CHAR_TRAITS