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Re: [patch] Remove unused code from dse.c.


On 03/29/2013 12:12 PM, Steven Bosscher wrote:
On Fri, Mar 29, 2013 at 6:29 PM, Jeff Law <law@redhat.com> wrote:
On 03/29/2013 11:24 AM, Lawrence Crowl wrote:

At what point did we stop setting clear_alias_sets?  Was that
intentional or not?


I do not know the answer to either question.

That's what needs to be determined before I'll approve.  It means digging a
bit.



My view is that we have already lost the feature.  The code
that populates the set is gone.  The remaining code has probably
suffered bitrot because it is not being tested.  Trying to recreate
the population will probably result in inconsistencies anyway,
necessitating a rewrite of the remaining code.  So, the remaining
code has little value, and might have negative value.

But that doesn't mean dropping the code is the right thing to do.  The right
thing to do is see if the feature was dropped on purpose.  If so, then we
remove this dead code.  If not, then we fix the real problem, namely the
code was accidentally disabled (and add suitable tests to the suite to catch
this kind of problem in the future).

It's left over cleanups from code removed last year:
http://gcc.gnu.org/ml/gcc-patches/2012-03/msg01862.html
More correctly, it's been dead since an Oct 2008 patch from Richard Henderson which introduced set_mem_attrs_for_spill which effectively provides the alias analysis code with the information it needs to disambiguate stack slots from everything else without the callback.

Lawrence, that's the critical bit of information you failed to provide.

Patch approved, please install.

Thanks,
Jeff


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