[PATCH] tree-optimization/98855 - redo BB vectorization costing

[Richard Sandiford]

Richard Biener <rguenther@suse.de> writes:
> On Fri, 5 Feb 2021, Richard Sandiford wrote:
>> Richard Biener <rguenther@suse.de> writes:
>> > +  /* First produce cost vectors sorted by loop index.  */
>> > +  auto_vec<std::pair<unsigned, stmt_info_for_cost *> >
>> > +    li_scalar_costs (scalar_costs.length ());
>> > +  auto_vec<std::pair<unsigned, stmt_info_for_cost *> >
>> > +    li_vector_costs (vector_costs.length ());
>> > +  FOR_EACH_VEC_ELT (scalar_costs, i, cost)
>> > +    {
>> > +      unsigned l = gimple_bb (cost->stmt_info->stmt)->loop_father->num;
>> > +      li_scalar_costs.quick_push (std::make_pair (l, cost));
>> > +    }
>> > +  unsigned l = li_scalar_costs[0].first;
>> 
>> Is this just to silence an unused warning?  Might be worth a comment if so
>> (although couldn't we just use 0?).
>
> The issue is that not all vector_costs entries have a stmt_info so 
> this uses a random loop also used in the scalar code (that's going
> to be the correct loop in case there's only one loop involved which
> is probably 99% of the cases).  I'mm add a comment.

Hmm, OK, but I thought the comment below was saying that all such
cases follow the relevant statement, instead of coming first.
Is this situation specific to the first run of costs?

Richard

>
>> > +  FOR_EACH_VEC_ELT (vector_costs, i, cost)
>> > +    {
>> > +      /* We inherit from the previous SI, invariants, externals and
>> > +	 extracts immediately follow the cost for the related stmt.  */
>> 
>> Looks like the comment predates s/SI/COST/.
>
> Indeed, will fix and push.
>
> Thanks,
> Richard.