Introducing LLVM's basic design principles and its history

LLVM is a notoriously didactic framework because of a high degree of organization in its several tools, which allows the curious user to observe many steps of the compilation. The design decisions go back to its first versions more than 10 years ago when the project, which had a strong focus on backend algorithms, relied on GCC to translate high-level languages, such as C, to the LLVM intermediate representation (IR). Today, a central aspect of the design of LLVM is its IR. It uses Single-Static Assignments (SSA), with two important characteristics:

• Code is organized as three-address instructions

• It has an infinite number of registers

This does not mean, however, that LLVM has a single form of representing the program. Throughout the compilation process, other intermediary data structures hold the program logic and help its translation across major checkpoints. Technically, they are also intermediate forms of program representation...