1. Dictionary generation for the Experiments
Velislava Spasova
Supervisor: Axel Naumann

2. Introduction to dictionaries
LHC data is C++ objects stored at disks
C++ provides very limited Runtime type information (RTTI)
A mechanism to describe reflection information for the objects’ classes is needed
Dictionaries are one such mechanism
Dictionaries are C++ source files generated from header files

3. Current Dictionary Generating Tools (rootcint)
Two dictionary generation tools – rootcint and genreflex
rootcint :
Uses CINT for the parsing of the header files
Selection information could be passed as a Linkdef.h file
Problems: CINT is limited in its parsing capabilities, templates processing could be problematic, etc.

4. Current Dictionary Generating Tools (genreflex)
genreflex is a Python script (1000s of lines)
Uses GCCXML to parse the header files – a temporary XML file describing the AST is created
XML selection files could be used for specification of the items for which a dictionary is to be generated
Problems: Slow and practically impossible to debug, creates an intermediate file between the header file and the dictionary which slows down even more the dictionary generation

5. LLVM and clang
LLVM - collection of compiler and tool-chain technologies
Used as an optimizer and code generator for different compiler front-ends
clang – compiler front-end for C, C++ and Objective-C
Uses LLVM as a back-end
Offers a C++ interface to C++ code
Is much faster than GCC
Benefits: enhanced language support, shortened build times, more dynamic access to C++

6. Proposed solution
Combine rootcint and genreflex functionality into one tool - rootcling using LLVM and clang

7. Requirements to rootcling
Should be a drop-in solution
The transition to the new tool should be transparent to the users
Shouldn’t break existing code
Should accept current mechanisms for dictionary selection (XML selection files or Linkdef.h files)

8. My task – dictionary selection
Create small (pseudo) XML parser to parse the selection.xml files used by genreflex
Create small parser to parse Linkdef.h files used by rootcint
Realize different selection policies corresponding to the different policies of rootcint and genreflex.
Realize the selection process based on the information in the selection files

9. Classes flow chart .

10. The role of clang
Provides access to the header through the clang::Decl class and its derivatives (“AST”)
Fast and reliable
Provides mechanism for recursive traversal of the AST
Overriding the DeclVisitor methods to check if a Decl* is to be selected and if yes, trigger the dictionary generation

11. Selection data structure
Selection criteria are represented as a hierarchy of Selection rules
Selection rules are created when parsing the selection files

12. Example Linkdef.h file #ifdef __CINT__ #pragma link off all globals;
#pragma link off all classes;
#pragma link off all functions;
#pragma link C++ nestedclasses;
#pragma link C++ class A+;
#pragma link C++ class B-!;
#pragma link C++ function n::get_n();
#pragma link C++ function n::set_values(int*, std::string&);
#pragma link C++ global var_a;
#pragma link C++ enum ETest;
#endif

13. Example selection.xml file
<lcgdict>
<selection>
<class name = “a” />
<class pattern=“std::vector<*” />
<class file = “test.h” />
<function proto_name = “n::get_n(float\*,int)” />
</selection>
<exclusion>
<class name = “a” >
<method proto_pattern = “set_value(*)” />
</class>
</exclusion>
</lcgdict>

14. Some complications …
rootcint and genreflex have different and complex default behavior
Should nested classes (A::B) inherit the selection rule for the outer class (A)? genreflex and rootcint allow for different behavior
Determine selection behavior of both tools experimentally

15. Selection flow chart

16. Progress and Future work
XML parser developed
Pattern recognition developed
Selection rule classes developed
Selection mechanism implemented
Future work:
Linkdef.h parser to be developed
Tests

17. Don’t hesitate to share any remarks, suggestions or questions

18. Thank you!