Re: tree decl stored during LGEN does not map to a symtab_node during WPA

[Erick Ochoa <eochoa@gcc.gnu.org>]

> There are entities, like SSA names and STRING_CSTs which are specially
> encoded and if you stream those in your LGEN data you have to set up
> appropriate encoders.  In general streaming arbitrary trees isn't the
> best thing to do, usually you're interested in specific pieces only.  That's
> especially true for things "local" to a function (like SSA names), I think
> existing IPA passes only stream encoded references to global entities
> (or parameters) and all "local" info is some pass specific data streamed
> as raw data, not trees.

Thanks!

>
> Why do you want to stream SSA trees for example?
>

I am working on a prototype for a points-to analysis where the
implementation is an IPA_PASS as opposed to a SIMPLE_IPA_PASS. It is
still somewhat early in the prototype implementation stages but I
would like to have SSA trees at WPA time as a way to map constraints
variables back to Gimple. The idea is to generate most constraints at
LGEN time (some will have to be updated) and solve them at WPA time.

Do you have any other suggestions on how to map constraint variables
(similar to the index in the varinfo_t array) back to Gimple (but now
as an IPA_PASS)? We have had similar discussions before, but now I am
looking at things more concretely, from the point of view of: how
exactly does one map the analysis back to Gimple while staying within
what is possible in the LTO framework?

I do have a pass-specific data structure, but it contains references
to trees. It is similar to varinfo_t, which has a decl. I also have
another tree for expressions (the concrete use case right now is
having a global variable being assigned to a string literal), and a
field for ssa variables, which was intended to store a reference to
the corresponding tree. Again, as a way to map back the constraint
variable to Gimple.

> There can be no
> references to those from other IPA entities?

I don't follow this question. I think this may be a statement and not
a question. Please clarify this for me, but perhaps the following
might answer: Since I am working on an interprocedural analysis, SSA
variables may point to abstract memory locations allocated in
different functions. So I need to have a link between SSA variables
and whatever memory locations they might point to.