[libc++] Updates the compilers used post LLVM-20 branching. #126564

mordante · 2025-02-10T18:11:56Z

Once LLVM 20 is released the clang-18 will no longer be supported.

mordante · 2025-02-10T18:12:28Z

@Zingam FYI this patch contains the documentation update.

llvmbot · 2025-02-10T18:12:30Z

@llvm/pr-subscribers-github-workflow

Author: Mark de Wever (mordante)

Changes

Once LLVM 20 is released the clang-18 will no longer be supported.

Full diff: https://github.com/llvm/llvm-project/pull/126564.diff

2 Files Affected:

(modified) .github/workflows/libcxx-build-and-test.yaml (+13-9)
(modified) libcxx/docs/index.rst (+8-8)

diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index ee77e83363d37a0..502ab35313dc7a7 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -48,8 +48,8 @@ jobs:
           'generic-cxx26',
           'generic-modules'
         ]
-        cc: [  'clang-20' ]
-        cxx: [ 'clang++-20' ]
+        cc: [  'clang-21' ]
+        cxx: [ 'clang++-21' ]
         include:
           - config: 'generic-gcc'
             cc: 'gcc-14'
@@ -88,18 +88,22 @@ jobs:
           'generic-cxx20',
           'generic-cxx23'
         ]
-        cc: [ 'clang-20' ]
-        cxx: [ 'clang++-20' ]
+        cc: [ 'clang-21' ]
+        cxx: [ 'clang++-21' ]
         include:
           - config: 'generic-gcc-cxx11'
             cc: 'gcc-14'
             cxx: 'g++-14'
-          - config: 'generic-cxx23'
-            cc: 'clang-18'
-            cxx: 'clang++-18'
+          - config: 'generic-cxx26'
+            cc: 'clang-20'
+            cxx: 'clang++-20'
           - config: 'generic-cxx26'
             cc: 'clang-19'
             cxx: 'clang++-19'
+          # Release transition
+          - config: 'generic-cxx23'
+            cc: 'clang-18'
+            cxx: 'clang++-18'
     steps:
       - uses: actions/checkout@v4
       - name: ${{ matrix.config }}
@@ -169,8 +173,8 @@ jobs:
       - name: ${{ matrix.config }}
         run: libcxx/utils/ci/run-buildbot ${{ matrix.config }}
         env:
-          CC: clang-20
-          CXX: clang++-20
+          CC: clang-21
+          CXX: clang++-21
       - uses: actions/upload-artifact@26f96dfa697d77e81fd5907df203aa23a56210a8 # v4.3.0
         if: always()
         with:
diff --git a/libcxx/docs/index.rst b/libcxx/docs/index.rst
index 37912e9f8d03e6b..58ff1232e97fac1 100644
--- a/libcxx/docs/index.rst
+++ b/libcxx/docs/index.rst
@@ -128,14 +128,14 @@ Libc++ aims to support common compilers that implement the C++11 Standard. In or
 good balance between stability for users and maintenance cost, testing coverage and development
 velocity, libc++ drops support for older compilers as newer ones are released.
 
-============ =============== ========================== =====================
-Compiler     Versions        Restrictions               Support policy
-============ =============== ========================== =====================
-Clang        17, 18, 19-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
-AppleClang   15                                         latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
-Open XL      17.1 (AIX)                                 latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
-GCC          14              In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_
-============ =============== ========================== =====================
+============ =================== ========================== =====================
+Compiler     Versions            Restrictions               Support policy
+============ =================== ========================== =====================
+Clang        18, 19, 20, 21-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
+AppleClang   15                                             latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
+Open XL      17.1 (AIX)                                     latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
+GCC          14                  In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_
+============ =================== ========================== =====================
 
 Libc++ also supports common platforms and architectures:

llvmbot · 2025-02-10T18:12:31Z

@llvm/pr-subscribers-libcxx

Author: Mark de Wever (mordante)

Changes

Once LLVM 20 is released the clang-18 will no longer be supported.

Full diff: https://github.com/llvm/llvm-project/pull/126564.diff

2 Files Affected:

(modified) .github/workflows/libcxx-build-and-test.yaml (+13-9)
(modified) libcxx/docs/index.rst (+8-8)

diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index ee77e83363d37a0..502ab35313dc7a7 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -48,8 +48,8 @@ jobs:
           'generic-cxx26',
           'generic-modules'
         ]
-        cc: [  'clang-20' ]
-        cxx: [ 'clang++-20' ]
+        cc: [  'clang-21' ]
+        cxx: [ 'clang++-21' ]
         include:
           - config: 'generic-gcc'
             cc: 'gcc-14'
@@ -88,18 +88,22 @@ jobs:
           'generic-cxx20',
           'generic-cxx23'
         ]
-        cc: [ 'clang-20' ]
-        cxx: [ 'clang++-20' ]
+        cc: [ 'clang-21' ]
+        cxx: [ 'clang++-21' ]
         include:
           - config: 'generic-gcc-cxx11'
             cc: 'gcc-14'
             cxx: 'g++-14'
-          - config: 'generic-cxx23'
-            cc: 'clang-18'
-            cxx: 'clang++-18'
+          - config: 'generic-cxx26'
+            cc: 'clang-20'
+            cxx: 'clang++-20'
           - config: 'generic-cxx26'
             cc: 'clang-19'
             cxx: 'clang++-19'
+          # Release transition
+          - config: 'generic-cxx23'
+            cc: 'clang-18'
+            cxx: 'clang++-18'
     steps:
       - uses: actions/checkout@v4
       - name: ${{ matrix.config }}
@@ -169,8 +173,8 @@ jobs:
       - name: ${{ matrix.config }}
         run: libcxx/utils/ci/run-buildbot ${{ matrix.config }}
         env:
-          CC: clang-20
-          CXX: clang++-20
+          CC: clang-21
+          CXX: clang++-21
       - uses: actions/upload-artifact@26f96dfa697d77e81fd5907df203aa23a56210a8 # v4.3.0
         if: always()
         with:
diff --git a/libcxx/docs/index.rst b/libcxx/docs/index.rst
index 37912e9f8d03e6b..58ff1232e97fac1 100644
--- a/libcxx/docs/index.rst
+++ b/libcxx/docs/index.rst
@@ -128,14 +128,14 @@ Libc++ aims to support common compilers that implement the C++11 Standard. In or
 good balance between stability for users and maintenance cost, testing coverage and development
 velocity, libc++ drops support for older compilers as newer ones are released.
 
-============ =============== ========================== =====================
-Compiler     Versions        Restrictions               Support policy
-============ =============== ========================== =====================
-Clang        17, 18, 19-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
-AppleClang   15                                         latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
-Open XL      17.1 (AIX)                                 latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
-GCC          14              In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_
-============ =============== ========================== =====================
+============ =================== ========================== =====================
+Compiler     Versions            Restrictions               Support policy
+============ =================== ========================== =====================
+Clang        18, 19, 20, 21-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
+AppleClang   15                                             latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
+Open XL      17.1 (AIX)                                     latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
+GCC          14                  In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_
+============ =================== ========================== =====================
 
 Libc++ also supports common platforms and architectures:

Once LLVM 20 is released the clang-18 will no longer be supported.

Zingam · 2025-02-12T06:59:57Z

@mordante I don't know if this is important. Regarding OpenXL compiler: According to the documentation they've changed the base LLVM version between minor versions: 17.1.2 is based on LLVM17 and 17.1.3 is based on LLVM19
https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.2?topic=whats-new
https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.3?topic=whats-new

philnik777 · 2025-02-12T08:34:12Z

.github/workflows/libcxx-build-and-test.yaml

+          # Release transition
+          - config: 'generic-cxx23'
+            cc: 'clang-18'
+            cxx: 'clang++-18'


Do we really need this? I don't think there is much code that requires clang-18-specific workarounds currently and it's really not clear to me when we should drop it otherwise.

Yes we need this. At the moment patches get actively backported to the release branch. Testing clang-18 enures that backporting is easy to do. Once LLVM 20.1.0 is released we can drop clang-18. (We've been doing this is the past too.)

I agree with @mordante, this is easy to keep around for a few weeks and it reduces friction when backporting.

I don't remember any rules on this and I though it was around for quite a while sometimes. If we agree that it can go after the initial release I'm fine with it, but I really don't want to keep it around for the whole cycle, since that would effectively extend our supported compilers by one version.

It's indeed only for the release transition.

philnik777 · 2025-02-12T08:34:40Z

libcxx/docs/index.rst

+============ =================== ========================== =====================
+Compiler     Versions            Restrictions               Support policy
+============ =================== ========================== =====================
+Clang        18, 19, 20, 21-git                             latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version


I don't think we should document that we support more versions than we plan to support when this gets released.

I prefer to keep this as is, and drop 18 when we no longer support it.

But we don't support it anymore. This is purely around for ease of migration.

mordante · 2025-02-12T16:56:21Z

@mordante I don't know if this is important. Regarding OpenXL compiler: According to the documentation they've changed the base LLVM version between minor versions: 17.1.2 is based on LLVM17 and 17.1.3 is based on LLVM19 https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.2?topic=whats-new https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.3?topic=whats-new

Thanks for the information! I feel this belongs in a separate patch and have it reviewed by somebody of IBM. Are you willing to create such a patch?

Zingam · 2025-02-13T15:17:02Z

@mordante I don't know if this is important. Regarding OpenXL compiler: According to the documentation they've changed the base LLVM version between minor versions: 17.1.2 is based on LLVM17 and 17.1.3 is based on LLVM19 https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.2?topic=whats-new https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.3?topic=whats-new

Thanks for the information! I feel this belongs in a separate patch and have it reviewed by somebody of IBM. Are you willing to create such a patch?

Thanks. Done: #127072

ldionne · 2025-02-18T16:49:23Z

libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp

@@ -12,7 +12,7 @@
 // UNSUPPORTED: c++03

 // TODO: Investigate these failures which break the CI.
-// UNSUPPORTED: clang-18, clang-19, clang-20
+// UNSUPPORTED: clang-18, clang-19, clang-20, clang-21


Let's revive the patch to remove this. It's been broken for 1.5 years. If nobody cares about it, we should get rid of it.

It's not been broken. Our CI is. This actually works for every clang version listed here, except in the CI.

Do we know why it does not work in our CI?

IIRC the last time it mostly worked except in the optimized build. I've disabled it for everything, since it was already the same day as the LLVM 20 branch and the test was already disabled for all the other versions. We should look into it and maybe just disable it for the optimized build.

) Once LLVM 20 is released the clang-18 will no longer be supported.

mordante requested a review from a team as a code owner February 10, 2025 18:11

llvmbot added libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. github:workflow labels Feb 10, 2025

[libc++] Updates the compilers used post LLVM-20 branching.

cb49571

Once LLVM 20 is released the clang-18 will no longer be supported.

mordante force-pushed the review/relase_branch_compiler_updates branch from eb74deb to cb49571 Compare February 11, 2025 18:36

philnik777 reviewed Feb 12, 2025

View reviewed changes

Fixes CI.

bd0d864

ehan701 approved these changes Feb 12, 2025

View reviewed changes

ldionne approved these changes Feb 18, 2025

View reviewed changes

mordante merged commit b22fc43 into llvm:main Feb 18, 2025
79 checks passed

mordante deleted the review/relase_branch_compiler_updates branch February 18, 2025 18:26

wldfngrs pushed a commit to wldfngrs/llvm-project that referenced this pull request Feb 19, 2025

[libc++] Updates the compilers used post LLVM-20 branching. (llvm#126564

95740ff

) Once LLVM 20 is released the clang-18 will no longer be supported.

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[libc++] Updates the compilers used post LLVM-20 branching. #126564

[libc++] Updates the compilers used post LLVM-20 branching. #126564

mordante commented Feb 10, 2025

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[libc++] Updates the compilers used post LLVM-20 branching. #126564

[libc++] Updates the compilers used post LLVM-20 branching. #126564

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mordante commented Feb 10, 2025

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mordante commented Feb 12, 2025

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