[patch] Preserving loops in threading (updated)

[Zdenek Dvorak]

Hello,

> I'm not totally happy with the first instance stuff; I went down this 
> path once and I don't think it's wise to have passes twiddling their
> behavior based on whether or not its the first pass or not.
> 
> I agree that we've got a reasonably compelling case for jump 
> threading, but I don't want to see other passes mimicking this
> behavior unless they've got a compelling case as well.  Can we
> bury the first instance stuff inside the threading code somehow?

I am not particularly happy about it, either; and I think I found a
cleaner solution -- once the project to preserve loop structures
throughout compilation is finished, we will be able to simply mark the
loops for that loop header copying or jump threading to loop latch edge
was performed, and avoid doing it again.

So the first instance stuff will be just a temporary hack (and I will
mark it as such in the comments, and add the warnings not to use it
on other places).

Zdenek

> Regardless of the answer to the previous question all the other
> changes are OK and can go in without delay.
> 
> Jeff
>