https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64410

--- Comment #8 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> (In reply to Marc Glisse from comment #1)
> > There are a number of things that make it complicated.
> > 1) gcc doesn't like to vectorize when the number of iterations is not known
> > at compile time.
> 
> Not an issue, we know it here (it's symbolic)

IIRC I tried modifying the original code by replacing all complex operations by
explicit scalar operations and it failed to vectorize, but worked when
replacing the number of iterations by a constant.

> > 3) the ABI for complex uses 2 separate double instead of a vector of 2
> > double.
> 
> I think that's unrelated.

Indeed, it's just that with a different ABI we could have been lucky and
stumbled upon the optimal code, almost by accident.

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