Compilation performance comparison of 3.5.0 and TreeSSA treeson MICO sources as requested in: [tree-ssa] Merge status 2004-05-03

[Andrew MacLeod]

On Mon, 2004-05-17 at 15:10, law@redhat.com wrote:
> In message < 1083800290.3350.6.camel@localhost.localdomain >, Diego Novillo write
> s:
>  >On Wed, 2004-05-05 at 19:33, Jan Hubicka wrote:
>  >
>  >> You need ssa form form DCE.  Going in/out just for DCE might be bit
>  >> expensive...
>  >> 
>  >Well, is it?  You probably don't even need the full out-of-ssa pass.  If
>  >at -O0 we only schedule passes the will never create overlapping LRs,
>  >you can just drop the SSA_NAMEs on the way out. 
> Right.  And DCE certainly doesn't create overlapping lifetimes.
> 
> 
> You know, we could actually make the "may create overlapping lifetime" a
> property of the optimization passes.  That way we just check the property
> at out-of-ssa time, if the property is clear, then we just drop the SSA_NAMES.
> 

That sounds like a very good idea. I would think that having
remove_ssa_form() check the property and decide whether to do what it
does now, or a small subset. You'd still want to perform TER on the way
out.  You would also lose any live range splitting that we currently get
(but at -O0 that wouldnt matter). 

Andrew