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Re: [PATCH] Fix IVOPTs problem

On Fri, 2005-08-05 at 11:48 +0200, Richard Guenther wrote:
> Compiling gcc.c-torture/execute/20010910-1.c with IVOPTs enabled
> leads to ssa verification failures because 
> tree-ssa-loop-ivopts.c:rewrite_use does not update ssa form
> (it calls update_stmt but misses mark_new_vars_to_rename).
But are the transformations performed by ivopts supposed to
be changing the aliasing information?

ie, the appearance of a new V_MAY_DEF indicates that the
aliasing information on that statement has changed.  So at
the heart of this patch is whether or not IVOPTS is allowed
to change a statement's aliasing properties.

If the answer is yes, then clearly this patch is OK.  If the
answer is no, then clearly this patch is not OK.  I tend to
think the former, mostly because we ran into a similar situation
with the vectorizer, but I'd like to be a little more sure.

I was going to try and do a little investigative work on my
own, but couldn't get 20010910-1.c to fail.  Do I need to
install some uncommitted patch (if so, a pointer would be
greatly appreciated).  Target triplet and compile-time
flags would be helpful too.


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