Eliminate adr+str InlineJITBlockHeader

What is the inlinejitblockheader for exactly?

> It's what we use for RIP reconstruction

Why can't we keep a table of host pc --> guest rip and just look at the regular backtrace?

> Once we support deferring async signals inside the JIT, we can
> I also did some benchmarking to see the overhead for the adr+str and it fell within noise. It's single cycle + single cycle so it is hard to beat

But on my end multiblock sped up bytemark a lot and I don't think DSE is the reason 😉

Tracker for later.

Start by tracing InlineJITBlockHeader and the adr+str sequence used for RIP reconstruction, then compare that path with the proposed host-PC-to-guest-RIP table and regular backtrace. Done would require a settled design that eliminates the header without regressing deferred async-signal support or the reported multiblock benchmark behavior.

Written by the indexing model from the issue text.