The SSA-based LLVM IR provides elegant representation for compiler analyses and transformations. However, it presents challenges to the OpenMP code generation in the LLVM backend, especially when the input program is compiled under different optimization levels. This paper presents a practical and effective framework on how to perform the OpenMP code generation based on the LLVM IR. In this presentation, we propose a canonical OpenMP loop representation under different optimization levels to preserve the OpenMP loop structure without being affected by compiler optimizations. A code-motion guard intrinsic is proposed to prevent code motion across OpenMP regions. In addition, a utility based on the LLVM SSA updater is presented to perform the SSA update during the transformation. Lastly, the scope alias information is used to preserve the alias relationship for backend-outlined functions. This framework has been implemented in Intel’s LLVM compiler.
