On Wed, 16 Sep 2015, Alan Lawrence wrote: > On 16/09/15 17:10, Bill Schmidt wrote: > > > > On Wed, 2015-09-16 at 16:29 +0100, Alan Lawrence wrote: > > > On 16/09/15 15:28, Bill Schmidt wrote: > > > > 2015-09-16 Bill Schmidt <wschm...@linux.vnet.ibm.com> > > > > > > > > * config/rs6000/altivec.md (UNSPEC_REDUC_SMAX, > > > > UNSPEC_REDUC_SMIN, > > > > UNSPEC_REDUC_UMAX, UNSPEC_REDUC_UMIN, UNSPEC_REDUC_SMAX_SCAL, > > > > UNSPEC_REDUC_SMIN_SCAL, UNSPEC_REDUC_UMAX_SCAL, > > > > UNSPEC_REDUC_UMIN_SCAL): New enumerated constants. > > > > (reduc_smax_v2di): New define_expand. > > > > (reduc_smax_scal_v2di): Likewise. > > > > (reduc_smin_v2di): Likewise. > > > > (reduc_smin_scal_v2di): Likewise. > > > > (reduc_umax_v2di): Likewise. > > > > (reduc_umax_scal_v2di): Likewise. > > > > (reduc_umin_v2di): Likewise. > > > > (reduc_umin_scal_v2di): Likewise. > > > > (reduc_smax_v4si): Likewise. > > > > (reduc_smin_v4si): Likewise. > > > > (reduc_umax_v4si): Likewise. > > > > (reduc_umin_v4si): Likewise. > > > > (reduc_smax_v8hi): Likewise. > > > > (reduc_smin_v8hi): Likewise. > > > > (reduc_umax_v8hi): Likewise. > > > > (reduc_umin_v8hi): Likewise. > > > > (reduc_smax_v16qi): Likewise. > > > > (reduc_smin_v16qi): Likewise. > > > > (reduc_umax_v16qi): Likewise. > > > > (reduc_umin_v16qi): Likewise. > > > > (reduc_smax_scal_<mode>): Likewise. > > > > (reduc_smin_scal_<mode>): Likewise. > > > > (reduc_umax_scal_<mode>): Likewise. > > > > (reduc_umin_scal_<mode>): Likewise. > > > > > > You shouldn't need the non-_scal reductions. Indeed, they shouldn't be > > > used if > > > the _scal are present. The non-_scal's were previously defined as > > > producing a > > > vector with one element holding the result and the other elements all > > > zero, and > > > this was only ever used with a vec_extract immediately after; the _scal > > > pattern > > > now includes the vec_extract as well. Hence the non-_scal patterns are > > > deprecated / considered legacy, as per md.texi. > > > > Thanks -- I had misread the description of the non-scalar versions, > > missing the part where the other elements are zero. What I really > > want/need is an optab defined as computing the maximum value in all > > elements of the vector. > > Yes, indeed. It seems reasonable to me that this would coexist with an optab > which computes only a single value (i.e. a scalar).
So just to clarify - you need to reduce the vector with max to a scalar but want the (same) result in all vector elements? > At that point it might be appropriate to change the cond-reduction code to > generate the reduce-to-vector in all cases, and optabs.c expand it to > reduce-to-scalar + broadcast if reduce-to-vector was not available. Along with > the (parallel) changes to cost model already proposed, does that cover all the > cases? It does add a new tree code, yes, but I'm feeling that could be > justified if we go down this route. I'd rather have combine recognize an insn that does both (if it exists). As I understand powerpc doesn't have reduction to scalar (I think no ISA actually has this, but all ISAs have reduce to one vector element plus a cheap way of extraction (effectively a subreg)) but it's reduction already has all result vector elements set to the same value (as opposed to having some undefined or zero or whatever). > However, another point that springs to mind: if you reduce a loop containing > OR or MUL expressions, the vect_create_epilog_for_reduction reduces these > using shifts, and I think will also use shifts for platforms not possessing a > reduc_plus/min/max. If shifts could be changed for rotates, the code there > would do your reduce-to-a-vector-of-identical-elements in the midend...can we > (sensibly!) bring all of these together? > > > Perhaps the practical thing is to have the vectorizer also do an > > add_stmt_cost with some new token that indicates the cost model should > > make an adjustment if the back end doesn't need the extract/broadcast. > > Targets like PowerPC and AArch32 could then subtract the unnecessary > > cost, and remove the unnecessary code in simplify-rtx. > > I think it'd be good if we could do it before simplify-rtx, really, although > I'm not sure I have a strong argument as to why, as long as we can cost it > appropriately. > > > In any case, I will remove implementing the deprecated optabs, and I'll > > also try to look at Alan L's patch shortly. > > That'd be great, thanks :) As for the cost modeling the simple solution is of course to have these as "high-level" costs (a new enum entry), but the sustainable solution is to have the target see the vectorized code and decide for itself. Iff we'd go down the simple route then the target may as well create the vectorized code for that special high-level operation itself. Richard.
