LTO build of rpcs3 fails

[oltolm]

Hello I use clang 19.1.7 from MSYS2 clang64. Recently https://github.com/RPCS3/rpcs3 has enabled LTO. Now the release build is failing with

[build] ld.lld: error: undefined symbol: thread-local initialization routine for perf_stat<19226358023673171ull>::g_tls_perf_stat
[build] >>> referenced by C:/src/rpcs3/rpcs3/Emu/CPU/CPUThread.cpp
[build] >>>               librpcs3_emu.a(CPUThread.cpp.obj)
[build] >>> referenced by C:/src/rpcs3/rpcs3/Emu/Memory/vm.cpp
[build] >>>               librpcs3_emu.a(vm.cpp.obj)
[build] 

[mstorsjo]

Hello I use clang 19.1.7 from MSYS2 clang64

Technically, this repo is for the llvm-mingw packaging, and for upstream Clang issues the relevant place is https://github.com/llvm/llvm-project/issues - but I guess the issue can be reproduced with plain llvm-mingw too.

In any case - in order to be able to dig further into it, can the issue be reduced down to a minimal selfcontained testcase?

[oltolm]

I reduced it

CMakeLists.txt:

cmake_minimum_required(VERSION 3.21)
project(lto VERSION 0.0.1 LANGUAGES C CXX)

add_executable(myexe src/myexe.cpp)
target_compile_features(myexe PRIVATE cxx_std_20)
target_link_options(myexe PRIVATE -municode)

set_property(TARGET myexe PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

myexe.cpp:

#include "perf_meter.hpp"

int wmain(int argc, wchar_t** argv)
{
    perf_meter<"DMA"_u32> perf_;
    return 0;
}

perf_meter.hpp:

template <auto ShortName> class perf_stat final {
    static inline thread_local struct perf_stat_local {
        // Local non-atomic values for increments
        unsigned m_log[66]{};

        perf_stat_local() noexcept {}

        ~perf_stat_local() {}

    } g_tls_perf_stat;

  public:
    static void push(unsigned start_time) noexcept { (void)g_tls_perf_stat; }
};

template <auto ShortName, auto... SubEvents> class perf_meter {
  public:
    ~perf_meter() { perf_stat<ShortName>::push(0); }
};

constexpr unsigned operator""_u32(const char* s, unsigned long long /*length*/)
{
    return 0;
}