[LLVMdev] some superoptimizer results

[John Regehr]

> Are you taking into account critical path length?

No, but of course that't not hard.  There are a lot of things that could 
be taken into account in the cost functions, but I was hoping to keep it 
really simple, so that the results would not be opaque.

> case all 3 instructions are dependent. So the former case can execute in 2 cycles while the latter takes
> 3. Modern OoO chips do in fact exploit this kind of thing.

Sure.  One way to deal with this would be to use the HW as its own model: 
run a lot of code fragments on real chips under a benchmark harness and 
then use the results to train a cost model.

John