LLVM’s overall JIT implementation and use cases
So far, we have only looked at ahead-of-time (AOT) compilers. These compilers compile the whole application. The application can only run after the compilation is finished. If the compilation is performed at the runtime of the application, then the compiler is a JIT compiler. A JIT compiler has interesting use cases:
- Implementation of a virtual machine: A programming language can be translated to byte code with an AOT compiler. At runtime, a JIT compiler is used to compile the byte code to machine code. The advantage of this approach is that the byte code is hardware-independent, and thanks to the JIT compiler, there is no performance penalty compared to an AOT compiler. Java and C# use this model today, but this is not a new idea: the USCD Pascal compiler from 1977 already used a similar approach.
- Expression evaluation: A spreadsheet application can compile often-executed expressions with a JIT compiler. For example...
