What to remove after tree-ssa is merged?

[Robert Dewar]

Andrew Pinski wrote:

> Should really PLACEHOLDER_EXPR be done in the front-end
> and be expanded to what it really does in gimplify stage
> which every other language needs to do with its language
> specific trees.

I don't think there is any clean translation here. Remember
that we tried this route energetically early on in Ada days
and failed, that is why PLACEHOLDER_EXPR was created to do
this task.

We really don't want that severe a mismatch between the
front end types and the back end types, a mismatch of that
level causes a lot of grief.

I am sure Richard can add more useful details here.