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

[Daniel Berlin]

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.
>