Re: [PATCH] tree-optimization/113552 - fix num_call accounting in simd clone vectorization

[Richard Biener <rguenther@suse.de>]

On Tue, 23 Jan 2024, Jakub Jelinek wrote:

> On Tue, Jan 23, 2024 at 12:56:52PM +0100, Richard Biener wrote:
> > The following avoids using exact_log2 on the number of SIMD clone calls
> > to be emitted when vectorizing calls since that can easily be not
> > a power of two in which case it will return -1.  For different simd
> > clones the number of calls will differ by a multiply with a power of two
> > only so using floor_log2 is good enough here.
> > 
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> > 
> > 	PR tree-optimization/113552
> > 	* tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
> > 	floor_log2 instead of exact_log2 on the number of calls.
> 
> Is there any target which supports non-power-of-two simdlen?
> If not, perhaps we should add !pow2p_hwi (num_calls) to the continue;
> condition a few lines earlier?

Is non-power-of-two simdlen a thing?  Note there's nothing wrong
with non-power-of-two num_calls, with VF == 4 and a group size
of 3 you get 12 lanes and either 3 (simdlen == 4) or 6 (simdlen == 2)
calls.

Iff non-power-of-two simdlen is a thing then we could bias
by + num_calls (no idea why we use *_log2 in the first place, but it
was that way since the beginning).

Richard.

> > diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> > index 09749ae3817..1dbe1115da4 100644
> > --- a/gcc/tree-vect-stmts.cc
> > +++ b/gcc/tree-vect-stmts.cc
> > @@ -4071,7 +4071,7 @@ vectorizable_simd_clone_call (vec_info *vinfo, stmt_vec_info stmt_info,
> >  	    || (nargs != simd_nargs))
> >  	  continue;
> >  	if (num_calls != 1)
> > -	  this_badness += exact_log2 (num_calls) * 4096;
> > +	  this_badness += floor_log2 (num_calls) * 4096;
> >  	if (n->simdclone->inbranch)
> >  	  this_badness += 8192;
> >  	int target_badness = targetm.simd_clone.usable (n);
> > -- 
> > 2.35.3
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)