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

[rguenther at suse dot de]

------- Comment #8 from rguenther at suse dot de  2007-09-27 14:01 -------
Subject: Re:  [4.3 Regression] aggregate DSE
 disabled

On Thu, 27 Sep 2007, dnovillo at google dot com wrote:

> ------- Comment #7 from dnovillo at google dot com  2007-09-27 13:48 -------
> Subject: Re:  [4.3 Regression] aggregate DSE disabled
> 
> On 27 Sep 2007 13:42:11 -0000, rguenth at gcc dot gnu dot org
> <gcc-bugzilla@gcc.gnu.org> wrote:
> 
> > Diego, it sucks that we need to jump through hoops to get V_MUST_DEF "back".
> 
> Unless we can prove that it is impossible to implement DSE any other
> way, I would prefer to keep virtual SSA as simple as possible.  It's
> meant as a safety net and a "good enough" UD web for passes that do
> not care for being too aggressive.

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.

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?

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33562