It there an equivalent to size_t in llvm

Some system libraries like malloc strlen want or return size_t as parameter.

• What is the right choice in LLVM IR to interact with these functions?
• Is the selection the task for the compiler?
• Does LLVM IR have a size_t type?

At the LLVM level, size_t doesn't exist. It is a construct for the benefit of the developer that is typedef'd to a native type. The native types have a fixed size for the target architecture and that is how the compiler represents them in LLVM bit code. So on x86, size_t might by viewed by the front end as unsigned long, which it then writes to LLVM as i32 (since LLVM assembly doesn't have an unsigned type).