Question about Gimple Variables named D.[0-9]*

Question about Gimple Variables named D.[0-9]*

[Erick Ochoa]

Hello,

I am looking at the dump for the build_alias pass. I see a lot of 
variables with the naming convention D.[0-9]* in the points-to sets 
being printed.

When I compile with

-fdump-tree-all-all

I can see that the suffix D.[0-9]* is appended to some gimple variables. 
I initially imagined that variables in the points-to variable set could 
map to a variable declaration in gimple, but this does not seem to be 
the case. I have confirmed this by searching for some known variable 
name in the points-to set and finding no matches in the gimple code, the 
other way around seems to also be true.

Are these variables just constraint variables used to solve the 
points-to analysis? In other words, the variables in points-to sets 
printed out in build_alias do not have a simple map to variables in 
gimple. The only relation is that the intersection between to points-to 
set for variable A with the points-to set of variable B will yield an 
is_alias(A, B) relationship. Is the above true?

Thanks!

Re: Question about Gimple Variables named D.[0-9]*

[Richard Biener]

On Thu, Aug 20, 2020 at 11:51 AM Erick Ochoa
<erick.ochoa@theobroma-systems.com> wrote:
>
> Hello,
>
> I am looking at the dump for the build_alias pass. I see a lot of
> variables with the naming convention D.[0-9]* in the points-to sets
> being printed.
>
> When I compile with
>
> -fdump-tree-all-all
>
> I can see that the suffix D.[0-9]* is appended to some gimple variables.
> I initially imagined that variables in the points-to variable set could
> map to a variable declaration in gimple, but this does not seem to be
> the case. I have confirmed this by searching for some known variable
> name in the points-to set and finding no matches in the gimple code, the
> other way around seems to also be true.
>
> Are these variables just constraint variables used to solve the
> points-to analysis? In other words, the variables in points-to sets
> printed out in build_alias do not have a simple map to variables in
> gimple. The only relation is that the intersection between to points-to
> set for variable A with the points-to set of variable B will yield an
> is_alias(A, B) relationship. Is the above true?

The points-to sets in SSA_NAME_POINTER_INFO record DECL_UIDs
which are those printed as D.[0-9]* which is appended to all variables
if you dump with -uid.  The points-to set "names" in the points-to dumps
are internal names created for the constraint vairables - most of the time
based on the program variable names but only loosely coupled.

The translation between constraint variables and program variables is
done in set_uids_in_ptset.

Richard.

>
> Thanks!
>
>