> * The interpreter should have a fast profiling mode (hashed counting of loop backedges) and a slower recording mode (for every instruction call the recorder first, then execute the instruction).
It already does this. The recording method is specialized for '[' (since loop headers can only be '['). All other opcodes go through a fast path that simply checks if we're in recording mode and stores to the trace buffer.
> * Don't record traces for a long time and then compile everything together.
The tricky part with this is knowing how to start up the profiler when we hit a side-exit. PC 123 may occur at multiple places in the trace tree. If we want to extend the tree on side-exit, we need to be able to recreate the path through the trace tree that led to that point. In essence, we need the compiled trace to continue updating the trace buffer. Certainly possible, but doesn't seem like a great idea offhand.
> * Sink all stores, especially updates of the virtual PC, data pointers etc. Don't count on the optimizer to do this for you.
Because I'm using tail-call based direct threading, there are no stores to the virtual PC or the data pointer. They're passed in registers to the tail-callee.
> * Due to the nature of the source language you may need to preprocess the IR or you need to teach the optimizer some additional tricks.
Yes, there's a whole range of pre-processing tricks that could be used to accelerate both the interpreter and the traces. I haven't even scratched the surface of that.
It already does this. The recording method is specialized for '[' (since loop headers can only be '['). All other opcodes go through a fast path that simply checks if we're in recording mode and stores to the trace buffer.
> * Don't record traces for a long time and then compile everything together.
The tricky part with this is knowing how to start up the profiler when we hit a side-exit. PC 123 may occur at multiple places in the trace tree. If we want to extend the tree on side-exit, we need to be able to recreate the path through the trace tree that led to that point. In essence, we need the compiled trace to continue updating the trace buffer. Certainly possible, but doesn't seem like a great idea offhand.
> * Sink all stores, especially updates of the virtual PC, data pointers etc. Don't count on the optimizer to do this for you.
Because I'm using tail-call based direct threading, there are no stores to the virtual PC or the data pointer. They're passed in registers to the tail-callee.
> * Due to the nature of the source language you may need to preprocess the IR or you need to teach the optimizer some additional tricks.
Yes, there's a whole range of pre-processing tricks that could be used to accelerate both the interpreter and the traces. I haven't even scratched the surface of that.