`./configure` fails for clang-14 on Ubuntu 23.10

hebasto commented at 5:08 pm on January 1, 2024: member

0$ clang-14 -v
1Ubuntu clang version 14.0.6
2Target: x86_64-pc-linux-gnu
3Thread model: posix
4InstalledDir: /usr/bin
5Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/13
6Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/13
7Candidate multilib: .;@m64
8Selected multilib: .;@m64

0$ ./configure CC=clang-14 CXX=clang++-14
1...
2checking whether std::atomic can be used without link library... no
3checking whether std::atomic needs -latomic... no
4configure: error: in `/bitcoin':
5configure: error: cannot figure out how to use std::atomic
6See `config.log' for more details

Here is an excerpt from the config.log:

 0configure:25695: checking whether std::atomic can be used without link library
 1configure:25722: clang++-14 -std=c++20 -o conftest -g -O2 -pthread   conftest.cpp  >&5
 2In file included from conftest.cpp:32:
 3/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48: error: call to consteval function 'std::chrono::hh_mm_ss::_S_fractional_width' is not a constant 
 4expression
 5        static constexpr unsigned fractional_width = {_S_fractional_width()};
 6                                                      ^
 7/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48: note: undefined function '_S_fractional_width' cannot be used in a constant expression
 8/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2275:2: note: declared here
 9        _S_fractional_width()
10        ^
111 error generated.

hebasto added the label Build system on Jan 1, 2024

maflcko commented at 10:37 am on January 2, 2024: member

That is a bug in clang-14, fixed in 15. Reproducer:

0template <class A>
1struct ch {
2    static consteval unsigned w() { return {}; };
3    static constexpr unsigned bar{w()};
4};
5
6int main() {}

maflcko commented at 11:02 am on January 2, 2024: member

I don’t understand why this isn’t caught by CI. Maybe libc++ somehow works around the bug in the corresponding clang?

Not sure how to fix it. The easiest would obviously be to bump the minimum required to clang-15. However, I am not sure if that works for macOS users.

hebasto commented at 11:10 am on January 2, 2024: member

I don’t understand why this isn’t caught by CI. Maybe libc++ somehow works around the bug in the corresponding clang?

We do not have a combination of clang-14 with libstdc++-13-dev in the CI.

fanquake commented at 11:15 am on January 2, 2024: member

Maybe libc++ somehow works around the bug in the corresponding clang?

The issue is only when Clang is being used with libstdc++. i.e:

0#include <chrono>
1
2int main() { return 0;}

 0clang-13 test.cpp -O2 -std=c++20
 1...
 2#include <...> search starts here:
 3 /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13
 4 /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/x86_64-linux-gnu/c++/13
 5 /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/backward
 6 /usr/lib/llvm-13/lib/clang/13.0.1/include
 7 /usr/local/include
 8 /usr/include/x86_64-linux-gnu
 9 /usr/include
10...
11In file included from test.cpp:1:
12/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48: error: call to consteval function 'std::chrono::hh_mm_ss::_S_fractional_width' is not a constant expression
13        static constexpr unsigned fractional_width = {_S_fractional_width()};
14                                                      ^
15/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48: note: undefined function '_S_fractional_width' cannot be used in a constant expression
16/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/chrono:2275:2: note: declared here
17        _S_fractional_width()
18        ^
191 error generated.

0clang-13 test.cpp -O2 -std=c++20 -stdlib=libc++
1...
2#include <...> search starts here:
3 /usr/lib/llvm-13/bin/../include/c++/v1
4 /usr/lib/llvm-13/lib/clang/13.0.1/include
5 /usr/local/include
6 /usr/include/x86_64-linux-gnu
7 /usr/include
8...

maflcko commented at 11:24 am on January 2, 2024: member

I don’t understand why this isn’t caught by CI. Maybe libc++ somehow works around the bug in the corresponding clang?

Oh, I guess libc++ doesn’t use consteval, but constexpr:

https://github.com/llvm/llvm-project/blob/9b7cf5bfb08b6e506216ef354dfd61adb15acbff/libcxx/include/__chrono/hh_mm_ss.h#L42

fanquake commented at 11:25 am on January 12, 2024: member

Going to close this as wontfix. If someone is using an operating system that is modern enough to be shipping GCC 13.2 and Clang 16 as the default compilers, then I’d suggest using either of those as their compiler. Also given that this is a bug in Clang, but only when coupled with a certain version of libstdc++, it’s not easy for us to “fix”. An alternative is to try with libc++. For older systems, clang-14 remains supported (for now).

fanquake closed this on Jan 12, 2024

./configure fails for clang-14 on Ubuntu 23.10 #29161

`./configure` fails for clang-14 on Ubuntu 23.10 #29161