[Bug tree-optimization/55334] [4.8 Regression] mgrid regression (ipa-cp disables vectorization)

[rguenther at suse dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55334

--- Comment #27 from rguenther at suse dot de <rguenther at suse dot de> 2013-02-19 13:49:30 UTC ---
On Tue, 19 Feb 2013, jamborm at gcc dot gnu.org wrote:

> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55334
> 
> --- Comment #26 from Martin Jambor <jamborm at gcc dot gnu.org> 2013-02-19 12:54:27 UTC ---
> (In reply to comment #25)
> > 
> > That won't work (read: it will cause miscompiles).  I believe with the
> > most recent data-dependence reorg I added a bunch of testcases that show
> > how to create breaking testcases ;)
> 
> Yes, it even already miscompiles a few testcases in the testsuite.  I
> mainly wanted to say that the vectorizer is not the only problem.
> Which means that we probably want to preserve restrict across IPA
> optimizations.
> 
> Another idea, which Honza mentioned last time I spoke to him, was that
> perhaps not lowering &x.u and other COMPONENT_REFs into MEM_REFs would
> be enough to figure out the accesses do not alias, but I am not sure
> that is true in gimple (or why tree-inline does this in the first
> place).

Yes, preserving COMPONENT_REFs would help here, but it is not
correct (even for this testcase the types do not match).

Richard.