Re: [PATCH][vectorizer][2/2] PR 65951: Hook up mult synthesis logic into vectorisation of mult-by-constant

[Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>]

On 14/06/16 08:04, Marc Glisse wrote:
> On Mon, 13 Jun 2016, Kyrill Tkachov wrote:
>
> > The new function vect_synth_mult_by_constant that does all the hard work is very similar in structure to expand_mult_const from expmed.c but it operates on gimple SSA rather than RTL.
>
> I think in some cases this transformation creates undefined overflow from well-defined code. While this is fine in RTL, I would expect to need a cast to unsigned_type_for in gimple for some of the algorithms.
> (not completely sure, just something to look at)

Would casting the initial argument to the unsigned type using fold_convert, performing the algorithm and then
casting the final result back to signed if necessary at the end work?

Kyrill