Sink function allocations, and then the activation allocation, to a point where we know that let-bound variables are initialized - and then allow those functions' code to be optimized without TDZ checks

[Filip Pizlo]

The optimizing compiler already has the ability to sink allocations to the point where they escape.  Doing this for activation and function allocations would enable us to prove cases where the function cannot see the TDZ of some let-bound variables.