[pypy-dev] Second compilation stage

[Hakan Ardo]

Hi,
there have been a bit of talk on improving loops with control flow,
i.e. when there is no single dominant path through the loop. To have
that discussion here let me make the following proposal (based on a
proposal from Armin):

How about aiming for something that starts out with running the
current JIT with the unrolling disabled. That will produce a graph of
traces which we could partition into one subgraph per loop. When we
believe all guards are either traced or never failing,  we use such
subgraphs as preambles. That is, we copy the full graph to producing a
peeled loop graph and optimized it. We focus the optimization on
removing the remaining guards as they (hopefully in most cases) are
loop invariant. Then we have a guard free graph of traces that we
could pass to gcc/llvm and the resulting machine code are attached
after the preamble.

If it turns out to be necessary, we could later add support for
handing guards to better support cases where we are unable optimize
them out.

-- 
Håkan Ardö