How does a retargetable compiler function?

A retargetable compiler functions by generating code for different types of computer hardware from a single source code.

A retargetable compiler is a type of compiler that can generate machine code for different types of computer hardware from a single source code. This is achieved by separating the process of compiling into two distinct stages: the front-end and the back-end. The front-end of the compiler is responsible for parsing the source code and generating an intermediate representation (IR). This IR is a low-level, hardware-independent representation of the source code.

The back-end of the compiler takes this IR and generates machine code that is specific to a particular type of hardware. This is where the 'retargetability' comes in. By swapping out the back-end of the compiler, you can generate code for different types of hardware. For example, you could have one back-end that generates code for x86 processors, another for ARM processors, and so on. The front-end of the compiler remains the same, as it is independent of the target hardware.

The advantage of this approach is that it allows software developers to write code once and then compile it for different types of hardware. This can save a significant amount of time and effort, as it eliminates the need to write and maintain separate versions of the code for each type of hardware. It also makes it easier to port software to new types of hardware, as only the back-end of the compiler needs to be updated.

However, retargetable compilers also have some limitations. The quality of the generated code can vary depending on the sophistication of the back-end. Some back-ends may be able to generate highly optimised code, while others may produce less efficient code. Additionally, while the front-end of the compiler is hardware-independent, it is not language-independent. Each programming language requires a different front-end, so a separate retargetable compiler is needed for each language.