[Bug tree-optimization/113441] [14 Regression] Fail to fold the last element with multiple loop

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113441

--- Comment #13 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 23 Jan 2024, juzhe.zhong at rivai dot ai wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113441
> 
> --- Comment #12 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
> (In reply to Richard Biener from comment #11)
> > (In reply to Tamar Christina from comment #9)
> > > There is a weird costing going on in the PHI nodes though:
> > > 
> > > m_108 = PHI <m_92(16), m_111(5)> 1 times vector_stmt costs 0 in body 
> > > m_108 = PHI <m_92(16), m_111(5)> 2 times scalar_to_vec costs 0 in prologue
> > > 
> > > they have collapsed to 0. which can't be right..
> > 
> > Note this is likely because of the backend going wrong.
> > 
> > bool
> > vectorizable_phi (vec_info *,
> >                   stmt_vec_info stmt_info, gimple **vec_stmt,
> >                   slp_tree slp_node, stmt_vector_for_cost *cost_vec)
> > {
> > ..
> > 
> >       /* For single-argument PHIs assume coalescing which means zero cost
> >          for the scalar and the vector PHIs.  This avoids artificially
> >          favoring the vector path (but may pessimize it in some cases).  */
> >       if (gimple_phi_num_args (as_a <gphi *> (stmt_info->stmt)) > 1)
> >         record_stmt_cost (cost_vec, SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node),
> >                           vector_stmt, stmt_info, vectype, 0, vect_body);
> > 
> > You could check if we call this with sane values.
> 
> Do you mean it's RISC-V backend cost model issue ?

I responded to Tamar which means a aarch64 cost model issue - the
specific issue that the PHIs appear to have no cost.  I didn't look
at any of the rest.