Needs optimization

[shashikdm]

The current implementation takes the entire trace of the cassette pass and operates on it. which makes it heavy in terms of space and time. possible improvement options:

1. generate the graph in-place during the cassette pass instead of a trace
2. do not trace function calls for functions in ignorelist.

@oxinabox can you help me with option 2?
Specifically how to tell Cassette to not overdub certain functions that may occur inside the called function?

[oxinabox]

Yep,
so say you want to ignore all functions called within foo
but not foo itself.

I believe you should be able to do:

Cassette.overdub(ctx::TraceCtx, ::typeof(foo), args...) = foo(args...)

since that will get rid of the default behavour of recursively overloading.

So to do a list of such functions.

for func in ignorelist
    @eval Cassette.overdub(ctx::TraceCtx, ::typeof($func), args...) = $func(args...)
end

BTW:
It might be easier to work with just overdub rather than prehook and posthook

function Cassette.overdub(ctx::TraceCtx, f, args...)
    enter!(ctx.metadata, f, args...)
    try
        if Cassette.canrecurse(f, args...)
            return Cassette.recurse(f, args...)
       else
           return Cassette.fallback(f, args...)
       end
    finally
        exit!(ctx.metadata, f, args...)
    end
end