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Re: [RFC] [autovect patch] Implement vectorization hints
> On Feb 27, 2005, at 1:22 PM, Zdenek Dvorak wrote:
> >In particular the node that you take in the
> >vect_pragma_lookup function may have been moved there by some code
> >motion optimization from elsewhere.
> That should not change info about node's source location (unless it is
> generated by compiler).
exactly. So you will use information about the original location,
thus applying the pragma to a wrong loop, thus causing a
> >Or the loop itself could be created
> >by some optimization (jump threading may do it sometimes).
> In such cases user can not give any hints :)
But he could give a hint to another loop, which now by simply mapping
the source locations applies to this new loop, again causing a
> >And these
> >are just those that occured to me, I am fairly sure there are more.
> I do not disagree. This is not straight forward, but unless plan is to
> attach pragma info with loop structures,
This would be probably the best solution, although also not without problems.
> I do not see any other very
> straight forward alternative. As soon as one says,
> User can put #pragma blah before the loop to give compiler hints...
> "before" brings in lot of edge cases.
There's not that much problem with formulation. Simply the statements
and line numbers may get swapped a lot during the optimizations, and
basing any information on them (especially the type of information that
is likely to cause problems if mistakenly attributed to a wrong object)
is very risky.