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

[jamborm at gcc dot gnu.org]

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).