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

On 6/5/06, Andrey Belevantsev <> wrote:
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

Can you add base numbers here, i.e. how many disambiguations are there in total for a and x?


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