[ tree-ssa] PRE problem

[Daniel Berlin]

> Seems reasonable.
>
> The problem is we do this substitution (reverse copy propagation) 
> *without*
> fixing up the annotation for method_signature.3.  Specifically, if we 
> do this
> kind of substitution we need to fix is_dereferenced_{load,store} and
> type_mem_tag in method_signature.3's annotation.
>

This is not copy propagation code.
It's verifying the safety of a rename.
We don't actually use the generated expressions except to check their 
versions in the part you are quoting.
So i'm not sure what problem this causes for you.
Are we actually generating and *inserting* an illegal expression?