alt Hacker News>V8 emits a near-jump for all forward jumps. If the target ends up too far away, the near-jump target is adjusted to a jump pool entry that contains a long-jump to the actual target
This sounds weird to me... Why not assume that all jumps need to be long to start with (so that the code is valid), then relax them to short jumps during an N-pass optimization stage- so that you get the smallest possible code?
Sounds like it's probably emitting the machine code in a single pass (compilation speed matters for a browser JIT), perhaps even together in a single pass with lowering (so don't even know the amount of instructions beforehand), and for such adjusting things afterwards would mean parsing & rewriting bytecode, and adjusting already-hardcoded backwards jump distances.