On Wed, Jul 21, 2021 at 6:55 PM Erick Ochoa <eoc...@gcc.gnu.org> wrote: > > Hello Richard, I need a little bit more help. In our previous messages > you mentioned "<function-encoder>" > > > > > > > > I guess the way to encode SSA trees would be to use sth like a > > > > <function-encoder>, SSA-version tuple much like PTA internally > > > > uses the varinfo array index as identifier for the variables in the > > > > constraints. For local decls (as opposed to SSA names) it's a bit > > > > more difficult - you'd have to devise your own encoding here. > > > > > > There was a little confusion on my part about what "encoder" meant > > > > > > You mention that I need to devise my own "encoder", but I am not sure > > > if we are conflating two notions: > > > > > > 1. encoding tree variables to constraint variables (i.e., a mapping of > > > some tuple (cgraph_node x symtab_node x ssa-version) to an integer > > > that represents the constraint variable) > > > 2. encoding as an implementation of a data structure used during LTO > > > to stream in and stream out trees/symbols to and from partitions. > > > (e.g., lto_symtab_encoder_t). > > > > And you proceed with the following answer > > > I meant 1) and streaming using the LTO cgraph encoder for the cgraph > > part and simply using the SSA version for the second part. > > > > From this exchange I understood that I should develop my own mapping > for ssa variables and local declarations. However, when dealing with > encoding a node which is available in the symbol table, I could use > the function lto_symtab_encoder_encode to map symbols to an integer > which would later make the symbol available at WPA time. Implicitly, > for me, this meant that this integer is the same for every distinct > symbol in different LGEN partitions. For example, if we encode symbol > X from partitions Y and we get the number N, then encoding symbol X in > partition Z should also yield N. > > I believe this is not the case, during WPA time I am printing: > 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 > > I think we had a previous discussion where it was mentioned that the > only way to distinguish between these cases is to look at varpool_node > cgraph_node: > > (From a different email edited for brevity) > > On Wed, 30 Jun 2021 at 19:38, Richard Biener <richard.guent...@gmail.com> > wrote: > > > > On June 30, 2021 6:28:29 PM GMT+02:00, Erick Ochoa <eoc...@gcc.gnu.org> > > wrote: > > >So how would I be able to say that two different declarations are the > > >same variable? > > > > By looking at the associated varpool node. > > > > Richard. > > > > 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. > 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. Richard.
