LOOP_HEADER tree code?

[Zdenek Dvorak]

Hello,

> >> You are proposing to complete the ssa representation such that
> >> foreach_ssa_uses also iterates over the niter information (a bit like vrp
> >> modifies the ssa chains with its extra assert information).  Wouldn't it
> >> be possible to not insert this niter information in the representation of
> >> the
> >> program (ie. not inserting a new tree node) but just modify the ssa
> >> iterators
> >> to also return the expressions that we store on the side?
> >
> >yes, it would be possible, however, possibly quite error-prone.
> >
> >> What are the other transformations that remove definitions that are not
> >> used?
> >
> >ivopts remove bivs that they replace, and I suspect that vectorizer
> >does something similar as well.  I do not know about other optimizers.
> >
> 
> The scev info has the same problem as the niter info, as we store it on
> the side, making it vulnerable to any code transform.  Now if we modify
> the var renaming, removal, ... aware of the information that we store
> on the side, we could avoid all these rather costly re-computations.

I did that once.  Updating scev info turned out to be more expensive than
recomputing it.

Zdenek