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

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

> > If this is the case, I can indeed get the varpool node's at WPA time
> > (as shown above), but comparing their pointer addresses will be
> > distinct. How can one find out that two varpool nodes/cgraph nodes are
> > the same at WPA time? Is just looking at the assembler name enough? I
> > of course want this to be safe.
>
> If they are the same they are merged by the symtab merging process done
> at WPA time.

I trust you, but how would I verify it myself? For example, I
mentioned that I printed:

> 1. pid of lgen process that generated the encoding
> 2. index returned by lto_symtab_encoder_encode
> 3. varpool_node->name ()
> 4. the pointer address being pointed by varpool node

and I got the same "name" but different indices, and different varpool
node's addresses for each of the lgen partitions. And of course
there's only one global variable with that name. In other words, what
exactly does it mean that they are "merged" and in which cases would
they not get merged?

What I'm seeing is for example:

fopen $PID1 8 $ADDR1
fopen $PID2 7 $ADDR2

where $PID1 != $PID2 (expected since it was seen in two LGEN
partitions). They were encoded as "8" and "7" in each of their LGEN
partitions. And when reading them and printing the address of
cgraph_node $ADDR1 != $ADDR2.

So, previously when I thought that merged implied that $ADDR1 ==
$ADDR2 this print shows that not to be the case. Also when I thought
that merging implied they would have the same number, the different
encoding showed that not to be the case. What I essentially want is
the following:

fopen $PID1 $ID
fopen $PID2 $ID

Where $ID can either be derived at WPA time or is encoded during LGEN.

I'm wondering if I should "merge" these two constraint variables by
checking their asm_name? I was just about to run an experiment to see
different cases for this (i.e., same named static function and print
their assembler name, etc.). This would be an example of $ID being
derived at WPA time by doing an O(n^2) comparison in the number of
functions, partitioning them into equivalent functions and then
assigning each of the distinct partitions an incremental ID.

>
> > Another question, how is this currently handled in other IPA passes?
> > Alternatively, do you have suggestions for encoding functions and
> > global variables in a similar way to how you suggested encoding ssa
> > variables and local declarations?
>
> I don't think any other pass has to encode SSA vars because those are
> strictly function local.  They only handle IP invariants aka addresses of
> globals or so.
>

For SSA vars I followed your suggestion of having a function encoding
and then using the SSA_VERSION number. Essentially <function encoding>
x ssa version. However, since both varpool and cgraph_node are encoded
in the same way (for which I am having problems), then the issue is
with the function encoding.