What to remove after tree-ssa is merged?

[Paul Brook]

On Wednesday 04 February 2004 9:28 pm, Richard Kenner wrote:
>     The information must be there somewhere. Whenever these size or bound
>     expressions are used, it surely must be in the context of a particular
>     object. The RTL expanders manage it quite happily.
>
> When they are *used*, sure.  But the point is that they are also present
> in the bounds expressions *to be used* and there is nothing they can be
> substituted with in that context.

To be used when?

I fail to see how this is a problem. The frontend passes complete functions to 
the optimizer. I agree that PLACEHOLDER_EXPR is a very useful in the frontend 
when building trees. However I can't see how it is of any use once the tree 
has been built.

Once the optimizers see a function, haven't we already determined all uses of 
these expressions? Do you have any examples of the when an optimier would 
unexpectedly decide it needs to use one of these expressions?

Paul