Re: [tree-ssa] Eliminating unnecessary variables during out-of-ssa

[Daniel Berlin <dberlin at dberlin dot org>]

On Monday, May 12, 2003, at 02:54  PM, Andrew MacLeod wrote:

> On Mon, 2003-05-12 at 14:43, Daniel Berlin wrote:
> > > Currently, I dont think we need anything that has a derefernced
> > > variable
> > > as a PHI_RESULT.
> >
> > For SSAPRE store movement and load movement, I need it.
> >
> > In particular, i need the vdefs for load movement, and the uses/phi
> > results for store movement.
> >
> > Otherwise, i can't tell when a load is possibly killed without
> > calculating the exact same info (in the case of vdefs), or the 
> > possible
> > insertion points for the store (that's what the PHI's give us).
> >
> > There are other optimizations i'm working on (loop related) that need
> > this info, too.
> >
> > Just because our basic opts don't need it, doesn't mean you should
> > remove it.
> > Can't you just ignore it in out-of-ssa, rather than remove it
> > altogether?
>
> Of course you need them for those optimizations, otherwise we wouldn't
> generate them in the first place.
:P
> After we go out of SSA form, we no longer have an SSA form, so no one
> needs these things. All PHI nodes are deleted as part of the process.
You said "Can anyone thing of when we might actually need any of these 
variables
in the rewriting stage?"
I was confused, because i usually think of the rewriting stage as 
into-ssa, not out-of-ssa.
>