[Bug tree-optimization/68315] ivdep has no effect in parloops

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68315

--- Comment #2 from vries at gcc dot gnu.org ---
(In reply to Richard Biener from comment #1)
> Yes.  The easiest way would be to make tree-data-ref.c use it I suppose.

Hmm, Jakub's comment at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46032#c21
is relevant to this PR:
... 
Note loop->safelen == INT_MAX is actually weaker than independent iterations,
when loop->safelen == INT_MAX, there can be dependencies, but only of certain
kinds, it says that it is equivalent if you run the loop normally and if you
run simultaneously (or emulated) the first statements of all the iterations,
then second statements and so on (so vectorize with any vectorization factor
the compiler wants).
...

So, I'd say we either mark this resolved-invalid, or we use this PR for
implementation of a "#pragma GCC ivdep independent" or something like that.