libgccjit is, despite its name, just another front-end for GIMPLE. The JIT-part is realized through compiling the object file to a shared library and using dlopen on this.

One big problem with libgccjit, despite its fairly bad compile-time performance, is that it's GPL-licensed and thereby makes the entire application GPL, which makes it impossible to use not just in proprietary use-cases but also in cases where incompatible licenses are involved.