[tree-ssa] Copy propagation [patch]

[Daniel Berlin]

On Friday, February 28, 2003, at 08:01  PM, Eric Christopher wrote:

>
>> You can cut down the copies during SSA form building, but we would 
>> still
>> need this as a separate pass to cleanup the garbage that PRE (and 
>> later
>> on GVN and VRP) may leave behind.
>>
>
> Well, one of the advantages that a hashed ssa gives you is the ability
> to get GVN for free, but your point still stands. :)
>

Errr, only hash based GVN (congruence class based GVN exists as well, 
and the two are not equal in what they remove, unfortunately).
Though it does also let you do value number based PRE and such.
On the flip side, hash based ssa isn't as easy to update, since you 
have to rehash new values, etc.

> -eric
>
> -- 
> o/~ Cry havoc... o/~
>