Improve robustness of dictionary to module lookups in ROOT


The LHC smashes groups of protons together at close to the speed of light: 40 million times per second and with seven times the energy of the most powerful accelerators built up to now. Many of these will just be glancing blows but some will be head on collisions and very energetic. When this happens some of the energy of the collision is turned into mass and previously unobserved, short-lived particles – which could give clues about how Nature behaves at a fundamental level - fly out and into the detector. Our work includes the experimental discovery of the Higgs boson, which leads to the award of a Nobel prize for the underlying theory that predicted the Higgs boson as an important piece of the standard model theory of particle physics.

CMS is a particle detector that is designed to see a wide range of particles and phenomena produced in high-energy collisions in the LHC. Like a cylindrical onion, different layers of detectors measure the different particles, and use this key data to build up a picture of events at the heart of the collision. The CMSSW is a collection of software for the CMS experiment. It is responsible for the collection and processing of information about the particle collisions at the detector. CMSSW uses the ROOT framework to provide support for data storage and processing. ROOT relies on Cling, Clang, LLVM for building automatically efficient I/O representation of the necessary C++ objects. The I/O properties of each object is described in a compilable C++ file called a /dictionary/. ROOT’s I/O dictionary system relies on C++ modules to improve the overall memory footprint when being used.

The few run time failures in the modules integration builds of CMSSW are due to dictionaries that can not be found in the modules system. These dictionaries are present as the mainstream system is able to find them using a broader search. The modules setup in ROOT needs to be extended to include a dictionary extension to track dictionary<->module mappings for C++ entities that introduce synonyms rather than declarations (using MyVector = std::vector<A<B>> where the dictionaries of A, B are elsewhere)

Task ideas

The project consists of the following tasks:


C/C++, Clang, LLVM, ROOT

Desirable Skills

Expected results

Develop functionality in ROOT’s TCling and rootcling classes which is capable of storing the ODRHash of a clang::Decl.

Candidate Guidelines and Evaluation

If you have interest in working on the project there is a list of things to do in order to maximize your chances to get selected:

  1. Contact the mentors and express interest in the project. Make sure you attach your CV;
  2. Download the source code of the project, build it and run the demos;
  3. Start familiarizing yourself with the codebase;
  4. If you have questions you can always contact a mentor.

For an evaluation task please contact the mentors.


ROOT CMSSW Compiler-Research clad llvm clang

Additional Information

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Participating Organizations