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Re: [tree-ssa] Insert on edge comment
On Fri, 2003-05-30 at 20:14, Daniel Berlin wrote:
>
>
> On Fri, 30 May 2003 law@redhat.com wrote:
> > >PRE will probably want to insert things on edge and commit them before
> > >we are done with PHI nodes :-) I suspect I'll need to add PHI node
> > >updating as a flag to the commit routine.
> > Yea. I haven't really thought about how hard the incremental update
> > will be.
>
> Well, PRE needs to see all the changes from an insertion immediately,
> especially because it's necessary to keep the ssa up to
> date and get strength reduction done properly.
>
Really? Doesn't that screw anything up when you insert on an edge and a
new basic block mystically appears? Originally I was doing it on
demand, but the magic new basic blocks screwed up some algorithms that
looped through basic blocks.
> >
> > The only nice property about PRE (at least those that I've worked on) is
> > that the stuff you're inserting on edges is straight-line code with no
> > control flow changes.
> We don't insert on edges almost ever.
>
really? what about the "almost" :-)
anyway, as long as straightline code is being done its not much of a
deal. The multiple-commit routines are really wrappers around an
on-demand edge insertion routine.
We need a whole new family of routines for inserting flow. I have spent
some time thinking about them.
Andrew