C++23 crash in DiagnosticInfo.h

[elmsheus]

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Description

I fully understand that ROOT 6.34/02 is not yet ready for the C++23 standard since it's explicitly disabled in the ROOT cmake configuration at https://github.com/root-project/root/blob/master/cmake/modules/CheckCompiler.cmake#L164C1-L164C43

I took my chances and have overwritten that setting and tried to compile ROOT 6.34/02 from source with gcc 14.2 and "-DCMAKE_CXX_STANDARD=23" in the ATLAS AnalysisBase configuration (https://gitlab.cern.ch/atlas/atlasexternals/-/blob/main/External/ROOT/CMakeLists.txt?ref_type=heads) and see the following compilation problem in ROOT/interpreter/llvm-project/llvm/include/llvm/IR/DiagnosticInfo.h:

[ 69%] Building CXX object interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/IRSimilarityIdentifier.cpp.o
In file included from /build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/Analysis/OptimizationRemarkEmitter.h:18,
                 from /build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/lib/Analysis/InlineCost.cpp:26:
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/IR/DiagnosticInfo.h: In instantiation of 'RemarkT& llvm::operator<<(RemarkT&&, std::enable_if_t<((bool)std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value), DiagnosticInfoOptimizationBase::Argument>) [with RemarkT = OptimizationRemarkMissed; std::enable_if_t<((bool)std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value), DiagnosticInfoOptimizationBase::Argument> = DiagnosticInfoOptimizationBase::Argument]':
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/lib/Analysis/InlineCost.cpp:2584:36:   required from here
 2584 |                  << NV("Callee", &F) << " has uninlinable pattern ("
      |                                    ^
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/IR/DiagnosticInfo.h:584:10: error: cannot bind non-const lvalue reference of type 'llvm::OptimizationRemarkMissed&' to an rvalue of type 'llvm::OptimizationRemarkMissed'
  584 |   return R;
      |          ^
In file included from /build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/Analysis/OptimizationRemarkEmitter.h:18,
                 from /build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/lib/Analysis/InlineAdvisor.cpp:19:
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/IR/DiagnosticInfo.h: In instantiation of 'RemarkT& llvm::operator<<(RemarkT&&, std::enable_if_t<((bool)std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value), StringRef>) [with RemarkT = OptimizationRemarkMissed; std::enable_if_t<((bool)std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value), StringRef> = StringRef]':
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/lib/Analysis/InlineAdvisor.cpp:94:19:   required from here
   94 |                << "'" << NV("Callee", Callee) << "' is not AlwaysInline into '"
      |                   ^~~
/build1/elmsheus/ana_20250206/root-build/src/ROOT/interpreter/llvm-project/llvm/include/llvm/IR/DiagnosticInfo.h:562:10: error: cannot bind non-const lvalue reference of type 'llvm::OptimizationRemarkMissed&' to an rvalue of type 'llvm::OptimizationRemarkMissed'
  562 |   return R;
      |          ^
gmake[6]: *** [interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/build.make:692: interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/InlineCost.cpp.o] Error 1
gmake[6]: *** Waiting for unfinished jobs....
gmake[6]: *** [interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/build.make:706: interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/InlineAdvisor.cpp.o] Error 1
[ 69%] Linking CXX static library ../../libLLVMCoverage.a
[ 69%] Built target LLVMCoverage
gmake[5]: *** [CMakeFiles/Makefile2:15517: interpreter/llvm-project/llvm/lib/Analysis/CMakeFiles/LLVMAnalysis.dir/all] Error 2
gmake[4]: *** [Makefile:156: all] Error 2
gmake[3]: *** [External/ROOT/CMakeFiles/ROOT.dir/build.make:93: src/ROOT-stamp/ROOT-build] Error 2
gmake[2]: *** [CMakeFiles/Makefile2:2373: External/ROOT/CMakeFiles/ROOT.dir/all] Error 2
gmake[1]: *** [CMakeFiles/Makefile2:2380: External/ROOT/CMakeFiles/ROOT.dir/rule] Error 2
gmake: *** [Makefile:1083: ROOT] Error 2

Reproducer

See above

ROOT version

6.34/02

Installation method

from source

Operating system

RHEL9.5

Additional context

No response

[ferdymercury]

Related PRs: #17253 and #17273

[guitargeek]

Hi @ferdymercury, thanks for the cross-referencing! Maybe you wanted to link two different PRs? You linked the same PR twice

[ferdymercury]

Yep, sorry, fixed.
The error in https://github.com/root-project/root/actions/runs/12327755238/job/34410152029?pr=17273 is the same one as reported here.

[hahnjo]

Note that this is a problem upstream, ie you currently cannot compile LLVM with -std=c++23. I think the issue related to this report is llvm/llvm-project#105778. But from trying to compile current main, it seems there are many more problems in the LLVM code base...

[hahnjo]

I started fixing the issues upstream (notably llvm/llvm-project#127400 for the issue described here) and this makes it work with GCC, but for Clang with C++23 there are many more problems. What I think we should be doing instead downstream in ROOT is always build LLVM with C++17: #17735 Then we only need to backport one of my upstream PRs to fix one header (llvm/llvm-project#127459) and fix RooFit (#17733) to get a working ROOT with C++23 🎉