Unlike trace trees, tracelets contain no control flow. It is just a type-specialized basic block. This means that the jit output does not combinatorially explode when we encounter polymorphism. In many ways, our approach is the opposite of tracing; we jit the first time we hit any code at all. And we look terrible on loopy microbench code, but run FB's multi million LOC application very well.
So it avoid trace explosion, and I would describe this as a sort-of local (in the compiler sense of "basic block") version of a method compiler. Can you compare the approaches?
The systems that it has the most in common with are actually binary translators; e.g., VMware's software x86 hypervisor, or the Dynamo system. Those systems run basic block at a time to solve a number of problems; e.g., disambiguation of code and data. We're basic-block-at-a-time for a different reason: closure under type inference.