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[Bug tree-optimization/33562] [4.3 Regression] aggregate DSE disabled

------- Comment #9 from dnovillo at google dot com  2007-09-27 14:12 -------
Subject: Re:  [4.3 Regression] aggregate DSE disabled

On 27 Sep 2007 14:01:18 -0000, rguenther at suse dot de
<> wrote:

> I sort-of agree.  Still DCE was able to handle tree-ssa/complex-4.c
> before we removed V_MUST_DEF.  Which is what I'm trying to get back.

Yeah, it is somewhat tempting to make the infrastructure more powerful
because you suddenly get more out of seemingly innocent passes.
However, a more powerful infrastructure creates problems of its own,
it needs to be maintained and it causes slowdowns even in passes that
do not need all the expressive power.

> As "good enough" UD web it would be nice to have only single VDEFs on
> stores (I don't care for clobbers at call sites).  Though finding the
> optimal static partitioning to ensure this is probably hard?

Yeah, that is the whole motivation behind the dynamic aspects of
mem-ssa, but getting it right has proven tricky.  Unfortunately, I
have not had time to come back to that idea in some time.


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