It's a backend for qemu's cpu JIT that doesn't actually JIT code for the host CPU, but code that's simply more performant to interpret than the target CPU arch as a set of JOP/ROP gadgets. It's so it works as perfomantly as possible without in case without the ability to set pages executable like on iOS.
https://github.com/tctiSH/qemu/blob/with_tcti_vectors/tcg/aa...