Index: libcxx/include/__bit/countr.h
===================================================================
--- libcxx/include/__bit/countr.h
+++ libcxx/include/__bit/countr.h
@@ -32,10 +32,8 @@
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 int __libcpp_ctz(unsigned long long __x) _NOEXCEPT { return __builtin_ctzll(__x); }
 
-#if _LIBCPP_STD_VER >= 20
-
-template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
+template <typename _Tp>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __countr_zero(_Tp __t) noexcept {
   if (__t == 0)
     return numeric_limits<_Tp>::digits;
 
@@ -56,6 +54,13 @@
   }
 }
 
+#if _LIBCPP_STD_VER >= 20
+
+template <__libcpp_unsigned_integer _Tp>
+_LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
+  return __countr_zero(__t);
+}
+
 template <__libcpp_unsigned_integer _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
   return __t != numeric_limits<_Tp>::max() ? std::countr_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
Index: libcxx/include/__numeric/gcd_lcm.h
===================================================================
--- libcxx/include/__numeric/gcd_lcm.h
+++ libcxx/include/__numeric/gcd_lcm.h
@@ -10,7 +10,9 @@
 #ifndef _LIBCPP___NUMERIC_GCD_LCM_H
 #define _LIBCPP___NUMERIC_GCD_LCM_H
 
+#include <__algorithm/min.h>
 #include <__assert>
+#include <__bit/countr.h>
 #include <__config>
 #include <__type_traits/common_type.h>
 #include <__type_traits/is_integral.h>
@@ -49,13 +51,26 @@
     _Result operator()(_Source __t) const noexcept { return __t; }
 };
 
-
-template<class _Tp>
-_LIBCPP_CONSTEXPR _LIBCPP_HIDDEN
-_Tp __gcd(_Tp __m, _Tp __n)
-{
+template <class _Tp>
+_LIBCPP_CONSTEXPR _LIBCPP_HIDDEN _Tp __gcd(_Tp __a, _Tp __b) {
     static_assert((!is_signed<_Tp>::value), "");
-    return __n == 0 ? __m : _VSTD::__gcd<_Tp>(__n, __m % __n);
+    if (__a == 0)
+        return __b;
+    if (__b == 0)
+        return __a;
+
+    int __az    = std::__countr_zero(__a);
+    int __bz    = std::__countr_zero(__b);
+    int __shift = std::min(__az, __bz);
+    __b >>= __bz;
+    while (__a != 0) {
+        __a >>= __az;
+        _Tp __absdiff = __a > __b ? __a - __b : __b - __a;
+        __b           = std::min(__a, __b);
+        __a           = __absdiff;
+        __az          = std::__countr_zero(__absdiff);
+    }
+    return __b << __shift;
 }
 
 template<class _Tp, class _Up>
Index: libcxx/test/libcxx/transitive_includes/cxx23.csv
===================================================================
--- libcxx/test/libcxx/transitive_includes/cxx23.csv
+++ libcxx/test/libcxx/transitive_includes/cxx23.csv
@@ -399,6 +399,7 @@
 numbers version
 numeric cmath
 numeric cstddef
+numeric initializer_list
 numeric limits
 numeric version
 optional compare
Index: libcxx/test/libcxx/transitive_includes/cxx26.csv
===================================================================
--- libcxx/test/libcxx/transitive_includes/cxx26.csv
+++ libcxx/test/libcxx/transitive_includes/cxx26.csv
@@ -188,6 +188,27 @@
 experimental/utility utility
 experimental/vector experimental/memory_resource
 experimental/vector vector
+ext/hash_map algorithm
+ext/hash_map cmath
+ext/hash_map cstddef
+ext/hash_map cstdint
+ext/hash_map cstring
+ext/hash_map functional
+ext/hash_map initializer_list
+ext/hash_map limits
+ext/hash_map new
+ext/hash_map stdexcept
+ext/hash_map string
+ext/hash_set algorithm
+ext/hash_set cmath
+ext/hash_set cstddef
+ext/hash_set cstdint
+ext/hash_set cstring
+ext/hash_set functional
+ext/hash_set initializer_list
+ext/hash_set limits
+ext/hash_set new
+ext/hash_set string
 filesystem compare
 filesystem cstddef
 filesystem cstdint
@@ -399,6 +420,7 @@
 numbers version
 numeric cmath
 numeric cstddef
+numeric initializer_list
 numeric limits
 numeric version
 optional compare