The article describes that the new JIT is a "copy-and-patch JIT" (I've previously heard this called a "splat JIT"). This is a relatively simple JIT architecture where you have essentially pre-compiled blobs of machine code for each interpreter instruction that you patch immediate arguments into by copying over them.

I once wrote an article about very simple JITs, and the first example in my article uses this style: https://blog.reverberate.org/2012/12/hello-jit-world-joy-of-...

I take some issue with this statement, made later in the article, about the pros/cons vs a "full" JIT:

> The big downside with a “full” JIT is that the process of compiling once into IL and then again into machine code is slow. Not only is it slow, but it is memory intensive.

I used to think this was true also, because my main exposure to JITs was the JVM, which is indeed memory-intensive and slow.

But then in 2013, a miraculous thing happened. LuaJIT 2.0 was released, and it was incredibly fast to JIT compile.

LuaJIT is undoubtedly a "full" JIT compiler. It uses SSA form and performs many optimizations (https://github.com/tarantool/tarantool/wiki/LuaJIT-Optimizat...). And yet feels no more heavyweight than an interpreter when you run it. It does not have any noticeable warm up time, unlike the JVM.

Ever since then, I've rejected the idea that JIT compilers have to be slow and heavyweight.