diff --git a/libcxx/include/__bit/bit_ceil.h b/libcxx/include/__bit/bit_ceil.h
--- a/libcxx/include/__bit/bit_ceil.h
+++ b/libcxx/include/__bit/bit_ceil.h
@@ -24,7 +24,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp bit_ceil(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp bit_ceil(_Tp __t) noexcept {
   if (__t < 2)
     return 1;
   const unsigned __n = numeric_limits<_Tp>::digits - std::countl_zero((_Tp)(__t - 1u));
diff --git a/libcxx/include/__bit/bit_floor.h b/libcxx/include/__bit/bit_floor.h
--- a/libcxx/include/__bit/bit_floor.h
+++ b/libcxx/include/__bit/bit_floor.h
@@ -23,7 +23,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp bit_floor(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp bit_floor(_Tp __t) noexcept {
   return __t == 0 ? 0 : _Tp{1} << std::__bit_log2(__t);
 }
 
diff --git a/libcxx/include/__bit/bit_width.h b/libcxx/include/__bit/bit_width.h
--- a/libcxx/include/__bit/bit_width.h
+++ b/libcxx/include/__bit/bit_width.h
@@ -22,7 +22,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int bit_width(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int bit_width(_Tp __t) noexcept {
   return __t == 0 ? 0 : std::__bit_log2(__t) + 1;
 }
 
diff --git a/libcxx/include/__bit/byteswap.h b/libcxx/include/__bit/byteswap.h
--- a/libcxx/include/__bit/byteswap.h
+++ b/libcxx/include/__bit/byteswap.h
@@ -23,7 +23,7 @@
 #if _LIBCPP_STD_VER >= 23
 
 template <integral _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
 
   if constexpr (sizeof(_Tp) == 1) {
     return __val;
diff --git a/libcxx/include/__bit/countl.h b/libcxx/include/__bit/countl.h
--- a/libcxx/include/__bit/countl.h
+++ b/libcxx/include/__bit/countl.h
@@ -86,12 +86,12 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
   return std::__countl_zero(__t);
 }
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
   return __t != numeric_limits<_Tp>::max() ? std::countl_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
 }
 
diff --git a/libcxx/include/__bit/countr.h b/libcxx/include/__bit/countr.h
--- a/libcxx/include/__bit/countr.h
+++ b/libcxx/include/__bit/countr.h
@@ -35,7 +35,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
   if (__t == 0)
     return numeric_limits<_Tp>::digits;
 
@@ -57,7 +57,7 @@
 }
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _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;
 }
 
diff --git a/libcxx/include/__bit/has_single_bit.h b/libcxx/include/__bit/has_single_bit.h
--- a/libcxx/include/__bit/has_single_bit.h
+++ b/libcxx/include/__bit/has_single_bit.h
@@ -24,7 +24,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr bool has_single_bit(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool has_single_bit(_Tp __t) noexcept {
   return __t != 0 && (((__t & (__t - 1)) == 0));
 }
 
diff --git a/libcxx/include/__bit/popcount.h b/libcxx/include/__bit/popcount.h
--- a/libcxx/include/__bit/popcount.h
+++ b/libcxx/include/__bit/popcount.h
@@ -35,7 +35,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr int popcount(_Tp __t) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int popcount(_Tp __t) noexcept {
   if (sizeof(_Tp) <= sizeof(unsigned int))
     return std::__libcpp_popcount(static_cast<unsigned int>(__t));
   else if (sizeof(_Tp) <= sizeof(unsigned long))
diff --git a/libcxx/include/__bit/rotate.h b/libcxx/include/__bit/rotate.h
--- a/libcxx/include/__bit/rotate.h
+++ b/libcxx/include/__bit/rotate.h
@@ -34,7 +34,7 @@
 #if _LIBCPP_STD_VER >= 20
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp rotl(_Tp __t, unsigned int __cnt) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotl(_Tp __t, unsigned int __cnt) noexcept {
   const unsigned int __dig = numeric_limits<_Tp>::digits;
   if ((__cnt % __dig) == 0)
     return __t;
@@ -42,7 +42,7 @@
 }
 
 template <__libcpp_unsigned_integer _Tp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp rotr(_Tp __t, unsigned int __cnt) noexcept {
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotr(_Tp __t, unsigned int __cnt) noexcept {
   return std::__rotr(__t, __cnt);
 }
 
diff --git a/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.compile.pass.cpp b/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.compile.pass.cpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_NODISCARD_EXT
+
+// Check that <bit> functions aren't marked [[nodiscard]] when
+// _LIBCPP_DISBALE_NODISCARD_EXT is defined
+
+#include <bit>
+
+void func() {
+  std::bit_ceil(0u);
+  std::bit_floor(0u);
+  std::bit_width(0u);
+  std::byteswap(0u);
+  std::countl_zero(0u);
+  std::countl_one(0u);
+  std::countr_zero(0u);
+  std::countr_one(0u);
+  std::has_single_bit(0u);
+  std::popcount(0u);
+  std::rotl(0u, 0);
+  std::rotr(0u, 0);
+}
diff --git a/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.verify.cpp b/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/bit.nodiscard_extensions.verify.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// check that <bit> functions are marked [[nodiscard]]
+
+#include <bit>
+
+void func() {
+  std::bit_ceil(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::bit_floor(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::bit_width(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::byteswap(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::countl_zero(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::countl_one(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::countr_zero(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::countr_one(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::has_single_bit(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::popcount(0u); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::rotl(0u, 0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::rotr(0u, 0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}