diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -24,16 +24,6 @@
 
 #ifdef __cplusplus
 
-#ifdef __GNUC__
-#  define _GNUC_VER (__GNUC__ * 100 + __GNUC_MINOR__)
-// The _GNUC_VER_NEW macro better represents the new GCC versioning scheme
-// introduced in GCC 5.0.
-#  define _GNUC_VER_NEW (_GNUC_VER * 10 + __GNUC_PATCHLEVEL__)
-#else
-#  define _GNUC_VER 0
-#  define _GNUC_VER_NEW 0
-#endif
-
 #define _LIBCPP_VERSION 14000
 
 #ifndef _LIBCPP_ABI_VERSION
@@ -509,22 +499,8 @@
 #define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK __attribute__((__no_sanitize__("unsigned-integer-overflow")))
 #endif
 
-#if __has_builtin(__builtin_launder)
-#define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
-#endif
-
-#if __has_builtin(__builtin_constant_p)
-#define _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
-#endif
-
 #define _LIBCPP_ALWAYS_INLINE __attribute__ ((__always_inline__))
 
-// Literal operators ""d and ""y are supported starting with LLVM Clang 8 and AppleClang 10.0.1
-#if (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER < 800) ||                 \
-    (defined(_LIBCPP_APPLE_CLANG_VER) && _LIBCPP_APPLE_CLANG_VER < 1001)
-#define _LIBCPP_HAS_NO_CXX20_CHRONO_LITERALS
-#endif
-
 #define _LIBCPP_DISABLE_EXTENSION_WARNING __extension__
 
 #elif defined(_LIBCPP_COMPILER_GCC)
@@ -547,11 +523,6 @@
 #define _LIBCPP_HAS_NO_ASAN
 #endif
 
-#if _GNUC_VER >= 700
-#define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
-#define _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
-#endif
-
 #define _LIBCPP_ALWAYS_INLINE __attribute__ ((__always_inline__))
 
 #define _LIBCPP_DISABLE_EXTENSION_WARNING __extension__
@@ -1275,7 +1246,7 @@
 #  define _LIBCPP_FALLTHROUGH() [[fallthrough]]
 #elif __has_cpp_attribute(clang::fallthrough)
 #  define _LIBCPP_FALLTHROUGH() [[clang::fallthrough]]
-#elif __has_attribute(fallthrough) || _GNUC_VER >= 700
+#elif __has_attribute(__fallthrough__)
 #  define _LIBCPP_FALLTHROUGH() __attribute__((__fallthrough__))
 #else
 #  define _LIBCPP_FALLTHROUGH() ((void)0)
@@ -1386,12 +1357,6 @@
 #  define _LIBCPP_FOPEN_CLOEXEC_MODE
 #endif
 
-#ifdef _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT_P
-#define _LIBCPP_BUILTIN_CONSTANT_P(x) __builtin_constant_p(x)
-#else
-#define _LIBCPP_BUILTIN_CONSTANT_P(x) false
-#endif
-
 // Support for _FILE_OFFSET_BITS=64 landed gradually in Android, so the full set
 // of functions used in cstdio may not be available for low API levels when
 // using 64-bit file offsets on LP32.
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -1496,11 +1496,8 @@
           typename _Base = __cxx_atomic_base_impl<_Tp> >
 #endif //_LIBCPP_ATOMIC_ONLY_USE_BUILTINS
 struct __cxx_atomic_impl : public _Base {
-
-#if _GNUC_VER >= 501
     static_assert(is_trivially_copyable<_Tp>::value,
       "std::atomic<Tp> requires that 'Tp' be a trivially copyable type");
-#endif
 
   _LIBCPP_INLINE_VISIBILITY __cxx_atomic_impl() _NOEXCEPT _LIBCPP_DEFAULT
   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR explicit __cxx_atomic_impl(_Tp value) _NOEXCEPT
diff --git a/libcxx/include/chrono b/libcxx/include/chrono
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -2907,7 +2907,7 @@
         return chrono::duration<long double, nano> (__ns);
     }
 
-#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CXX20_CHRONO_LITERALS)
+#if _LIBCPP_STD_VER > 17
     constexpr chrono::day operator ""d(unsigned long long __d) noexcept
     {
         return chrono::day(static_cast<unsigned>(__d));
diff --git a/libcxx/include/new b/libcxx/include/new
--- a/libcxx/include/new
+++ b/libcxx/include/new
@@ -337,11 +337,7 @@
 {
     static_assert (!(is_function<_Tp>::value), "can't launder functions" );
     static_assert (!(is_same<void, typename remove_cv<_Tp>::type>::value), "can't launder cv-void" );
-#ifdef _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER
     return __builtin_launder(__p);
-#else
-    return __p;
-#endif
 }
 
 #if _LIBCPP_STD_VER > 14
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2373,7 +2373,7 @@
 basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* __s, size_type __n)
 {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string::assign received nullptr");
-    return (_LIBCPP_BUILTIN_CONSTANT_P(__n) && __n < __min_cap)
+    return (__builtin_constant_p(__n) && __n < __min_cap)
                ? __assign_short(__s, __n)
                : __assign_external(__s, __n);
 }
@@ -2578,7 +2578,7 @@
 basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* __s)
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::assign received nullptr");
-    return _LIBCPP_BUILTIN_CONSTANT_P(*__s)
+    return __builtin_constant_p(*__s)
                ? (traits_type::length(__s) < __min_cap
                       ? __assign_short(__s, traits_type::length(__s))
                       : __assign_external(__s, traits_type::length(__s)))
diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -3049,135 +3049,10 @@
 
 // template <class T, class... Args> struct is_constructible;
 
-#if defined(_LIBCPP_COMPILER_GCC) && _GNUC_VER_NEW >= 10000
-# define _LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE
-#endif
-
-#if !defined(_LIBCPP_CXX03_LANG) && !__has_feature(is_constructible) && !defined(_LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE)
-
-template <class _Tp, class... _Args>
-struct __libcpp_is_constructible;
-
-template <class _To, class _From>
-struct __is_invalid_base_to_derived_cast {
-  static_assert(is_reference<_To>::value, "Wrong specialization");
-  using _RawFrom = __uncvref_t<_From>;
-  using _RawTo = __uncvref_t<_To>;
-  static const bool value = _And<
-        _IsNotSame<_RawFrom, _RawTo>,
-        is_base_of<_RawFrom, _RawTo>,
-        _Not<__libcpp_is_constructible<_RawTo, _From>>
-  >::value;
-};
-
-template <class _To, class _From>
-struct __is_invalid_lvalue_to_rvalue_cast : false_type {
-  static_assert(is_reference<_To>::value, "Wrong specialization");
-};
-
-template <class _ToRef, class _FromRef>
-struct __is_invalid_lvalue_to_rvalue_cast<_ToRef&&, _FromRef&> {
-  using _RawFrom = __uncvref_t<_FromRef>;
-  using _RawTo = __uncvref_t<_ToRef>;
-  static const bool value = _And<
-      _Not<is_function<_RawTo>>,
-      _Or<
-        _IsSame<_RawFrom, _RawTo>,
-        is_base_of<_RawTo, _RawFrom>>
-    >::value;
-};
-
-struct __is_constructible_helper
-{
-    template <class _To>
-    static void __eat(_To);
-
-    // This overload is needed to work around a Clang bug that disallows
-    // static_cast<T&&>(e) for non-reference-compatible types.
-    // Example: static_cast<int&&>(declval<double>());
-    // NOTE: The static_cast implementation below is required to support
-    //  classes with explicit conversion operators.
-    template <class _To, class _From,
-              class = decltype(__eat<_To>(declval<_From>()))>
-    static true_type __test_cast(int);
-
-    template <class _To, class _From,
-              class = decltype(static_cast<_To>(declval<_From>()))>
-    static integral_constant<bool,
-        !__is_invalid_base_to_derived_cast<_To, _From>::value &&
-        !__is_invalid_lvalue_to_rvalue_cast<_To, _From>::value
-    > __test_cast(long);
-
-    template <class, class>
-    static false_type __test_cast(...);
-
-    template <class _Tp, class ..._Args,
-        class = decltype(_Tp(declval<_Args>()...))>
-    static true_type __test_nary(int);
-    template <class _Tp, class...>
-    static false_type __test_nary(...);
-
-    template <class _Tp, class _A0, class = decltype(::new _Tp(declval<_A0>()))>
-    static is_destructible<_Tp> __test_unary(int);
-    template <class, class>
-    static false_type __test_unary(...);
-};
-
-template <class _Tp, bool = is_void<_Tp>::value>
-struct __is_default_constructible
-    : decltype(__is_constructible_helper::__test_nary<_Tp>(0))
-{};
-
-template <class _Tp>
-struct __is_default_constructible<_Tp, true> : false_type {};
-
-template <class _Tp>
-struct __is_default_constructible<_Tp[], false> : false_type {};
-
-template <class _Tp, size_t _Nx>
-struct __is_default_constructible<_Tp[_Nx], false>
-    : __is_default_constructible<typename remove_all_extents<_Tp>::type>  {};
-
-template <class _Tp, class... _Args>
-struct __libcpp_is_constructible
-{
-  static_assert(sizeof...(_Args) > 1, "Wrong specialization");
-  typedef decltype(__is_constructible_helper::__test_nary<_Tp, _Args...>(0))
-      type;
-};
-
-template <class _Tp>
-struct __libcpp_is_constructible<_Tp> : __is_default_constructible<_Tp> {};
-
-template <class _Tp, class _A0>
-struct __libcpp_is_constructible<_Tp, _A0>
-    : public decltype(__is_constructible_helper::__test_unary<_Tp, _A0>(0))
-{};
-
-template <class _Tp, class _A0>
-struct __libcpp_is_constructible<_Tp&, _A0>
-    : public decltype(__is_constructible_helper::
-    __test_cast<_Tp&, _A0>(0))
-{};
-
-template <class _Tp, class _A0>
-struct __libcpp_is_constructible<_Tp&&, _A0>
-    : public decltype(__is_constructible_helper::
-    __test_cast<_Tp&&, _A0>(0))
-{};
-
-#endif
-
-#if __has_feature(is_constructible) || defined(_LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE)
 template <class _Tp, class ..._Args>
 struct _LIBCPP_TEMPLATE_VIS is_constructible
     : public integral_constant<bool, __is_constructible(_Tp, _Args...)>
-    {};
-#else
-template <class _Tp, class... _Args>
-struct _LIBCPP_TEMPLATE_VIS is_constructible
-    : public __libcpp_is_constructible<_Tp, _Args...>::type {};
-#endif
+{ };
 
 #if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
 template <class _Tp, class ..._Args>
@@ -3250,53 +3125,12 @@
 
 // is_trivially_constructible
 
-#if __has_feature(is_trivially_constructible) || _GNUC_VER >= 501
-
 template <class _Tp, class... _Args>
 struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible
     : integral_constant<bool, __is_trivially_constructible(_Tp, _Args...)>
 {
 };
 
-#else  // !__has_feature(is_trivially_constructible)
-
-template <class _Tp, class... _Args>
-struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible
-    : false_type
-{
-};
-
-template <class _Tp>
-struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp>
-#if __has_feature(has_trivial_constructor) || defined(_LIBCPP_COMPILER_GCC)
-    : integral_constant<bool, __has_trivial_constructor(_Tp)>
-#else
-    : integral_constant<bool, is_scalar<_Tp>::value>
-#endif
-{
-};
-
-template <class _Tp>
-struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, _Tp&&>
-    : integral_constant<bool, is_scalar<_Tp>::value>
-{
-};
-
-template <class _Tp>
-struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, const _Tp&>
-    : integral_constant<bool, is_scalar<_Tp>::value>
-{
-};
-
-template <class _Tp>
-struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, _Tp&>
-    : integral_constant<bool, is_scalar<_Tp>::value>
-{
-};
-
-#endif // !__has_feature(is_trivially_constructible)
-
-
 #if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
 template <class _Tp, class... _Args>
 _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_constructible_v
@@ -3341,37 +3175,10 @@
 
 // is_trivially_assignable
 
-#if __has_feature(is_trivially_assignable) || _GNUC_VER >= 501
-
 template <class _Tp, class _Arg>
 struct is_trivially_assignable
     : integral_constant<bool, __is_trivially_assignable(_Tp, _Arg)>
-{
-};
-
-#else  // !__has_feature(is_trivially_assignable)
-
-template <class _Tp, class _Arg>
-struct is_trivially_assignable
-    : public false_type {};
-
-template <class _Tp>
-struct is_trivially_assignable<_Tp&, _Tp>
-    : integral_constant<bool, is_scalar<_Tp>::value> {};
-
-template <class _Tp>
-struct is_trivially_assignable<_Tp&, _Tp&>
-    : integral_constant<bool, is_scalar<_Tp>::value> {};
-
-template <class _Tp>
-struct is_trivially_assignable<_Tp&, const _Tp&>
-    : integral_constant<bool, is_scalar<_Tp>::value> {};
-
-template <class _Tp>
-struct is_trivially_assignable<_Tp&, _Tp&&>
-    : integral_constant<bool, is_scalar<_Tp>::value> {};
-
-#endif // !__has_feature(is_trivially_assignable)
+{ };
 
 #if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
 template <class _Tp, class _Arg>
diff --git a/libcxx/include/variant b/libcxx/include/variant
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -233,10 +233,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-// TODO: GCC 5 lies about its support for C++17 (it says it supports it but it
-//       really doesn't). That breaks variant, which uses some C++17 features.
-//       Remove this once we drop support for GCC 5.
-#if _LIBCPP_STD_VER > 14 && !(defined(_LIBCPP_COMPILER_GCC) && _GNUC_VER_NEW < 6000)
+#if _LIBCPP_STD_VER > 14
 
 // Light N-dimensional array of function pointers. Used in place of std::array to avoid
 // adding a dependency.
diff --git a/libcxx/src/include/atomic_support.h b/libcxx/src/include/atomic_support.h
--- a/libcxx/src/include/atomic_support.h
+++ b/libcxx/src/include/atomic_support.h
@@ -24,7 +24,7 @@
                        && defined(__ATOMIC_ACQ_REL)                  \
                        && defined(__ATOMIC_SEQ_CST)
 #   define _LIBCPP_HAS_ATOMIC_BUILTINS
-#elif !defined(__clang__) && defined(_GNUC_VER) && _GNUC_VER >= 407
+#elif defined(_LIBCPP_COMPILER_GCC)
 #   define _LIBCPP_HAS_ATOMIC_BUILTINS
 #endif
 
diff --git a/libcxx/src/locale.cpp b/libcxx/src/locale.cpp
--- a/libcxx/src/locale.cpp
+++ b/libcxx/src/locale.cpp
@@ -261,13 +261,6 @@
 #endif // _LIBCPP_NO_EXCEPTIONS
 }
 
-// NOTE avoid the `base class should be explicitly initialized in the
-// copy constructor` warning emitted by GCC
-#if defined(__clang__) || _GNUC_VER >= 406
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wextra"
-#endif
-
 locale::__imp::__imp(const __imp& other)
     : facets_(max<size_t>(N, other.facets_.size())),
       name_(other.name_)
@@ -278,10 +271,6 @@
             facets_[i]->__add_shared();
 }
 
-#if defined(__clang__) || _GNUC_VER >= 406
-#pragma GCC diagnostic pop
-#endif
-
 locale::__imp::__imp(const __imp& other, const string& name, locale::category c)
     : facets_(N),
       name_("*")
diff --git a/libcxxabi/src/include/atomic_support.h b/libcxxabi/src/include/atomic_support.h
--- a/libcxxabi/src/include/atomic_support.h
+++ b/libcxxabi/src/include/atomic_support.h
@@ -28,7 +28,7 @@
                        && defined(__ATOMIC_ACQ_REL)                  \
                        && defined(__ATOMIC_SEQ_CST)
 #   define _LIBCXXABI_HAS_ATOMIC_BUILTINS
-#elif !defined(__clang__) && defined(_GNUC_VER) && _GNUC_VER >= 407
+#elif defined(_LIBCPP_COMPILER_GCC)
 #   define _LIBCXXABI_HAS_ATOMIC_BUILTINS
 #endif