[AIX] cxx_std_23 is currently not a known feature to ibm-clang

[jakeegan]

Temporary workaround for the following CMake error:

CMake Error in /llvm/libcxx/benchmarks/CMakeLists.txt:
The compiler feature "cxx_std_23" is not known to CXX compiler
"IBMClang"

[llvmbot]

@llvm/pr-subscribers-libcxx

Changes

Temporary workaround for the following CMake error:

CMake Error in /llvm/libcxx/benchmarks/CMakeLists.txt:
The compiler feature "cxx_std_23" is not known to CXX compiler
"IBMClang"

---

Full diff: https://github.com/llvm/llvm-project/pull/66952.diff

1 Files Affected:

• (modified) libcxx/benchmarks/CMakeLists.txt (+3-1)

diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt
index ccc98df638ae397..05467dca23e50dc 100644
--- a/libcxx/benchmarks/CMakeLists.txt
+++ b/libcxx/benchmarks/CMakeLists.txt
@@ -81,7 +81,9 @@ add_library(               cxx-benchmarks-flags INTERFACE)
 # requesting `cxx_std_23` results in an error -- somehow CMake fails to
 # translate the `c++23` flag into `c++latest`, and the highest numbered C++
 # version that MSVC flags support is C++20.
-if (MSVC)
+# ibm-clang does not recognize the cxx_std_32 flag, so use this as a temporary
+# workaround on AIX as well.
+if (MSVC OR ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   add_compile_options(/std:c++latest)
 else()
   target_compile_features( cxx-benchmarks-flags INTERFACE cxx_std_23)

[ldionne]

What version of Clang are you folks using on the AIX builders?

[ldionne]

LGTM but we should figure out why cxx_std_23 doesn't work. I suspect that's a CMake problem if passing -std=c++23 actually works.

[jakeegan]

What version of Clang are you folks using on the AIX builders?

For upstream, we use a version of clang 15. For downstream (where we see this issue), we use ibm-clang 17.1.2.

LGTM but we should figure out why cxx_std_23 doesn't work. I suspect that's a CMake problem if passing -std=c++23 actually works.

Thanks! Yes, this is just a temporary fix, but we plan on investigating further.

[ldionne]

What version of Clang are you folks using on the AIX builders?

For upstream, we use a version of clang 15. For downstream (where we see this issue), we use ibm-clang 17.1.2.

LGTM but we should figure out why cxx_std_23 doesn't work. I suspect that's a CMake problem if passing -std=c++23 actually works.

Thanks! Yes, this is just a temporary fix, but we plan on investigating further.

Ok, great! Could you folks update your upstream compiler to 16? We're about to drop support for Clang 15 since Clang 17 has been released.

[jakeegan]

What version of Clang are you folks using on the AIX builders?

For upstream, we use a version of clang 15. For downstream (where we see this issue), we use ibm-clang 17.1.2.

LGTM but we should figure out why cxx_std_23 doesn't work. I suspect that's a CMake problem if passing -std=c++23 actually works.

Thanks! Yes, this is just a temporary fix, but we plan on investigating further.

Ok, great! Could you folks update your upstream compiler to 16? We're about to drop support for Clang 15 since Clang 17 has been released.

Yes we have plans to update it soon. Thanks for the heads up.