Re: [Patch Ping] [RFC] Alias export patch

[Andrey Belevantsev <abel at ispras dot ru>]

Richard Guenther wrote:
> I wonder how/if you deal with the problem that the tree loop optimizers
> (ivopts mostly) generate new pointers as induction variables but we don't
> run may_alias after them, so possibly all interesting (performance wise)
> pointers do not have updated points-to information?  Do your numbers
> (not performance) improve if you specify -fno-tree-loop-optimize?

Since the patch was created, we wanted to insert an additional 
pass_may_alias before going out of ssa to cope with this problem. 
However, as ivopts does not keep the points-to information updated, this 
does not work -- gcc ICEs in verify_ssa.  We've tried several times to 
turn off pass_loop_optimize and insert an extra may alias pass, and that 
didn't change much performance wise.  Now I've tried that once again. 
It gives the following (for x86):

   before (with ivopts)       after (no ivopts, extra alias pass)
bootstrap       SPEC         bootstrap       SPEC
C = 433         C = 26       C = 435         C = 32
O = 523         O = 52       O = 523         O = 49
a = 10563       a = 11691    a = 10607       a = 45750
x = 1954        x = 1035     x = 2148        x = 1200

C  --- add_coalesce is called for pointers with different points-to sets
O  --- add_coalesce is called when one pointer has a points-to set and 
the other has not
a  --- new disambiguations from extended alias sets when
alias_sets_conflict_p is called
x  --- new disambiguations from saved points-to sets when *_dependence 
is called

All the data is with patched add_coalesce and it is almost the same with 
unpatched one (as you can see from the previous mail).  This data shows 
~10% increase in new disambiguations from saved points-to sets, and 
somehow 4x increase for SPEC using extended alias sets (probably because 
of eon, but I haven't checked yet).  Also, I haven't tried what that 
gives us performance wise, but will do in a few days.

Andrey