[libc++] Disable cv-qualified arithmetic hash specializations #155786

philnik777 · 2025-08-28T08:38:11Z

#140407 accidentally enabled hash for cv-qualified types. This patch disables these specializations again.

llvmbot · 2025-08-28T08:38:47Z

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

#140407 accidentally enabled hash for cv-qualified types. This patch disables these specializations again.

Full diff: https://github.com/llvm/llvm-project/pull/155786.diff

7 Files Affected:

(modified) libcxx/include/CMakeLists.txt (+1)
(modified) libcxx/include/__functional/hash.h (+10-4)
(added) libcxx/include/__type_traits/is_unqualified.h (+25)
(modified) libcxx/include/module.modulemap.in (+1)
(modified) libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp (+5)
(modified) libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp (+5)
(modified) libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp (+5)

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 6fd16419f0c49..1f91b4828d4d3 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -872,6 +872,7 @@ set(files
   __type_traits/is_trivially_relocatable.h
   __type_traits/is_unbounded_array.h
   __type_traits/is_union.h
+  __type_traits/is_unqualified.h
   __type_traits/is_unsigned.h
   __type_traits/is_valid_expansion.h
   __type_traits/is_void.h
diff --git a/libcxx/include/__functional/hash.h b/libcxx/include/__functional/hash.h
index 489a6f00b8a3d..d95b2c0884984 100644
--- a/libcxx/include/__functional/hash.h
+++ b/libcxx/include/__functional/hash.h
@@ -21,6 +21,7 @@
 #include <__type_traits/is_enum.h>
 #include <__type_traits/is_floating_point.h>
 #include <__type_traits/is_integral.h>
+#include <__type_traits/is_unqualified.h>
 #include <__type_traits/underlying_type.h>
 #include <__utility/pair.h>
 #include <__utility/swap.h>
@@ -355,7 +356,8 @@ struct __hash_impl {
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value> > : __unary_function<_Tp, size_t> {
+struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value && __is_unqualified_v<_Tp>> >
+    : __unary_function<_Tp, size_t> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
     using type = __underlying_type_t<_Tp>;
     return hash<type>()(static_cast<type>(__v));
@@ -363,17 +365,21 @@ struct __hash_impl<_Tp, __enable_if_t<is_enum<_Tp>::value> > : __unary_function<
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_integral<_Tp>::value && (sizeof(_Tp) <= sizeof(size_t))> >
+struct __hash_impl<
+    _Tp,
+    __enable_if_t<is_integral<_Tp>::value && __is_unqualified_v<_Tp> && (sizeof(_Tp) <= sizeof(size_t))> >
     : __unary_function<_Tp, size_t> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 };
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_integral<_Tp>::value && (sizeof(_Tp) > sizeof(size_t))> >
+struct __hash_impl<_Tp,
+                   __enable_if_t<is_integral<_Tp>::value && __is_unqualified_v<_Tp> && (sizeof(_Tp) > sizeof(size_t))> >
     : __scalar_hash<_Tp> {};
 
 template <class _Tp>
-struct __hash_impl<_Tp, __enable_if_t<is_floating_point<_Tp>::value> > : __scalar_hash<_Tp> {
+struct __hash_impl<_Tp, __enable_if_t<is_floating_point<_Tp>::value && __is_unqualified_v<_Tp> > >
+    : __scalar_hash<_Tp> {
   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
     // -0.0 and 0.0 should return same hash
     if (__v == 0.0f)
diff --git a/libcxx/include/__type_traits/is_unqualified.h b/libcxx/include/__type_traits/is_unqualified.h
new file mode 100644
index 0000000000000..7970b3611601f
--- /dev/null
+++ b/libcxx/include/__type_traits/is_unqualified.h
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
+#define _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+inline const bool __is_unqualified_v = __is_same(_Tp, __remove_cvref(_Tp));
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___TYPE_TRAITS_IS_UNQUALIFIED_H
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index ee18d04c78d0e..c50c4dd73d4bb 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -335,6 +335,7 @@ module std_core [system] {
       header "__type_traits/is_union.h"
       export std_core.type_traits.integral_constant
     }
+    module is_unqualified { header "__type_traits/is_unqualified.h" }
     module is_unsigned {
       header "__type_traits/is_unsigned.h"
       export std_core.type_traits.integral_constant
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
index fd1fbe5f113ba..b796960975ea1 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
@@ -19,6 +19,7 @@
 #include <limits>
 #include <type_traits>
 
+#include "poisoned_hash_helper.h"
 #include "test_macros.h"
 
 enum class Colors { red, orange, yellow, green, blue, indigo, violet };
@@ -33,6 +34,10 @@ template <class T>
 void
 test()
 {
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
index b8f85e193dc8f..bf3e38e619519 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
@@ -25,12 +25,17 @@
 #include <limits>
 #include <cmath>
 
+#include "poisoned_hash_helper.h"
 #include "test_macros.h"
 
 template <class T>
 void
 test()
 {
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
index 14af7093c1e36..cfa6b324ba323 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
@@ -24,12 +24,17 @@
 #include <limits>
 #include <type_traits>
 
+#include "poisoned_hash_helper.h"
 #include "test_macros.h"
 
 template <class T>
 void
 test()
 {
+    test_hash_disabled<const T>();
+    test_hash_disabled<volatile T>();
+    test_hash_disabled<const volatile T>();
+
     typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");

github-actions · 2025-08-28T08:41:45Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff origin/main HEAD --extensions cpp,h -- libcxx/include/__type_traits/is_unqualified.h libcxx/include/__functional/hash.h libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp

⚠️
The reproduction instructions above might return results for more than one PR
in a stack if you are using a stacked PR workflow. You can limit the results by
changing origin/main to the base branch/commit you want to compare against.
⚠️

View the diff from clang-format here.

diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
index 05a19329f..e854bc363 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/enum.pass.cpp
@@ -38,12 +38,12 @@ void
 test()
 {
 #if TEST_STD_VER >= 11
-    test_hash_disabled<const T>();
-    test_hash_disabled<volatile T>();
-    test_hash_disabled<const volatile T>();
+  test_hash_disabled<const T>();
+  test_hash_disabled<volatile T>();
+  test_hash_disabled<const volatile T>();
 #endif
 
-    typedef std::hash<T> H;
+  typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
index f6c31d068..b96fbbb68 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/floating.pass.cpp
@@ -36,12 +36,12 @@ void
 test()
 {
 #if TEST_STD_VER >= 11
-    test_hash_disabled<const T>();
-    test_hash_disabled<volatile T>();
-    test_hash_disabled<const volatile T>();
+  test_hash_disabled<const T>();
+  test_hash_disabled<volatile T>();
+  test_hash_disabled<const volatile T>();
 #endif
 
-    typedef std::hash<T> H;
+  typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "");
diff --git a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
index c798b3aa7..7fb9a953d 100644
--- a/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/unord.hash/integral.pass.cpp
@@ -35,12 +35,12 @@ void
 test()
 {
 #if TEST_STD_VER >= 11
-    test_hash_disabled<const T>();
-    test_hash_disabled<volatile T>();
-    test_hash_disabled<const volatile T>();
+  test_hash_disabled<const T>();
+  test_hash_disabled<volatile T>();
+  test_hash_disabled<const volatile T>();
 #endif
 
-    typedef std::hash<T> H;
+  typedef std::hash<T> H;
 #if TEST_STD_VER <= 17
     static_assert((std::is_same<typename H::argument_type, T>::value), "");
     static_assert((std::is_same<typename H::result_type, std::size_t>::value), "");

ldionne

LGTM, thanks for the fix!

philnik777 · 2025-08-29T16:14:01Z

/cherry-pick 8a65c4f

llvmbot · 2025-08-29T16:20:04Z

/pull-request #156054

…55786) llvm#140407 accidentally enabled `hash` for cv-qualified types. This patch disables these specializations again. (cherry picked from commit 8a65c4f)

llvm/llvm-project#155786

`libcxx`: backport llvm/llvm-project#155476, llvm/llvm-project#147389, llvm/llvm-project#155786

philnik777 requested a review from a team as a code owner August 28, 2025 08:38

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Aug 28, 2025

philnik777 mentioned this pull request Aug 28, 2025

[libc++] Simplify the implementation of std::hash #140407

Merged

philnik777 changed the title ~~[libc++] Disabled cv-qualified arithmetic hash specializations~~ [libc++] Disable cv-qualified arithmetic hash specializations Aug 28, 2025

philnik777 added this to the LLVM 21.x Release milestone Aug 28, 2025

github-project-automation bot added this to LLVM Release Status Aug 28, 2025

github-project-automation bot moved this to Needs Triage in LLVM Release Status Aug 28, 2025

philnik777 force-pushed the disable_qualified_hashes branch from 88f028b to a8083ac Compare August 28, 2025 11:42

ldionne approved these changes Aug 28, 2025

View reviewed changes

github-project-automation bot moved this from Needs Triage to Needs Merge in LLVM Release Status Aug 28, 2025

[libc++] Disabled cv-qualified arithmetic hash specializations

565cf2a

philnik777 force-pushed the disable_qualified_hashes branch from a8083ac to 565cf2a Compare August 29, 2025 08:29

philnik777 merged commit 8a65c4f into llvm:main Aug 29, 2025
70 of 74 checks passed

github-project-automation bot moved this from Needs Merge to Done in LLVM Release Status Aug 29, 2025

philnik777 deleted the disable_qualified_hashes branch August 29, 2025 16:13

dwblaikie mentioned this pull request Sep 16, 2025

port 5b4819e to release #159209

Merged

jhuber6 mentioned this pull request Sep 17, 2025

[LLVM] Update CUDA ELF flags for their new ABI #159451

Merged

alexrp added a commit to alexrp/zig that referenced this pull request Oct 14, 2025

libcxx: backport llvm/llvm-project#155786

bc58b5d

llvm/llvm-project#155786

alexrp mentioned this pull request Oct 14, 2025

libcxx: backport llvm/llvm-project#155476, llvm/llvm-project#147389, llvm/llvm-project#155786 ziglang/zig#25572

Merged

alexrp added a commit to ziglang/zig that referenced this pull request Oct 14, 2025

Merge pull request #25572 from alexrp/libcxx-backports

27a396d

`libcxx`: backport llvm/llvm-project#155476, llvm/llvm-project#147389, llvm/llvm-project#155786

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[libc++] Disable cv-qualified arithmetic hash specializations #155786

[libc++] Disable cv-qualified arithmetic hash specializations #155786

Uh oh!

philnik777 commented Aug 28, 2025

Uh oh!

llvmbot commented Aug 28, 2025

Uh oh!

github-actions bot commented Aug 28, 2025 •

edited

Loading

Uh oh!

ldionne left a comment

Uh oh!

Uh oh!

philnik777 commented Aug 29, 2025

Uh oh!

llvmbot commented Aug 29, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

[libc++] Disable cv-qualified arithmetic hash specializations #155786

[libc++] Disable cv-qualified arithmetic hash specializations #155786

Uh oh!

Conversation

philnik777 commented Aug 28, 2025

Uh oh!

llvmbot commented Aug 28, 2025

Uh oh!

github-actions bot commented Aug 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

ldionne left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

philnik777 commented Aug 29, 2025

Uh oh!

llvmbot commented Aug 29, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

github-actions bot commented Aug 28, 2025 •

edited

Loading