Re: [PATCH] tree-optimization/108314 - avoid BIT_NOT optimization for extract-last

[Richard Biener <rguenther@suse.de>]

On Tue, 10 Jan 2023, Richard Sandiford wrote:

> Richard Biener <rguenther@suse.de> writes:
> > The extract-last reduction internal function expects the then and
> > else clause as vector and scalar and thus we cannot perform optimization
> > of the inversion of the condition by swapping the then/else clauses.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu, OK?
> 
> Sorry for not having found the time to look at the PR yet.
> Like you say in the trail, it seems kind-of familiar.
> 
> I think we should instead prevent the else in:
> 
> 	  scalar_cond_masked_key cond (cond_expr, ncopies);
> 	  if (loop_vinfo->scalar_cond_masked_set.contains (cond))
> 	    masks = &LOOP_VINFO_MASKS (loop_vinfo);
> 	  else
> 	    {
> 
> for EXTRACT_LAST.  We've lost as soon as swap_cond_operands gets
> set to true.

But we're not getting there - the above is guarded with

      if (reduction_type == EXTRACT_LAST_REDUCTION) 
        masks = &LOOP_VINFO_MASKS (loop_vinfo); 
      else
        {

instead we run into

      if (masked)
        vec_compare = vec_cond_lhs;
      else
        {
          vec_cond_rhs = vec_oprnds1[i];
          if (bitop1 == NOP_EXPR)
            {
...
          else
            {
...
              else if (bitop2 == BIT_NOT_EXPR
                {
                  /* Instead of doing ~x ? y : z do x ? z : y.  */
                  vec_compare = new_temp;
                  std::swap (vec_then_clause, vec_else_clause);

so we could instead reject vectorizing for EQ_EXPR but then
applying the negation to the condition allows this to be
vectorized just fine (which is what the patch does)?

Richard.

> Thanks,
> Richard
> 
> > Thanks,
> > Richard.
> >
> > 	PR tree-optimization/108314
> > 	* tree-vect-stmts.cc (vectorizable_condition): Do not
> > 	perform BIT_NOT_EXPR optimization for EXTRACT_LAST_REDUCTION.
> >
> > 	* gcc.dg/vect/pr108314.c: New testcase.
> > ---
> >  gcc/testsuite/gcc.dg/vect/pr108314.c | 16 ++++++++++++++++
> >  gcc/tree-vect-stmts.cc               | 13 +++++++++----
> >  2 files changed, 25 insertions(+), 4 deletions(-)
> >  create mode 100644 gcc/testsuite/gcc.dg/vect/pr108314.c
> >
> > diff --git a/gcc/testsuite/gcc.dg/vect/pr108314.c b/gcc/testsuite/gcc.dg/vect/pr108314.c
> > new file mode 100644
> > index 00000000000..07260e06915
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/vect/pr108314.c
> > @@ -0,0 +1,16 @@
> > +/* { dg-do compile } */
> > +/* { dg-additional-options "-march=armv9-a" { target aarch64-*-* } } */
> > +
> > +int x, y, z;
> > +
> > +void f(void)
> > +{
> > +  int t = 4;
> > +  for (; x; x++)
> > +    {
> > +      if (y)
> > +	continue;
> > +      t = 0;
> > +    }
> > +  z = t;
> > +}
> > diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> > index 6ddd41fb473..eb4ca1f184e 100644
> > --- a/gcc/tree-vect-stmts.cc
> > +++ b/gcc/tree-vect-stmts.cc
> > @@ -10677,7 +10677,8 @@ vectorizable_condition (vec_info *vinfo,
> >  	      vect_finish_stmt_generation (vinfo, stmt_info, new_stmt, gsi);
> >  	      if (bitop2 == NOP_EXPR)
> >  		vec_compare = new_temp;
> > -	      else if (bitop2 == BIT_NOT_EXPR)
> > +	      else if (bitop2 == BIT_NOT_EXPR
> > +		       && reduction_type != EXTRACT_LAST_REDUCTION)
> >  		{
> >  		  /* Instead of doing ~x ? y : z do x ? z : y.  */
> >  		  vec_compare = new_temp;
> > @@ -10686,9 +10687,13 @@ vectorizable_condition (vec_info *vinfo,
> >  	      else
> >  		{
> >  		  vec_compare = make_ssa_name (vec_cmp_type);
> > -		  new_stmt
> > -		    = gimple_build_assign (vec_compare, bitop2,
> > -					   vec_cond_lhs, new_temp);
> > +		  if (bitop2 == BIT_NOT_EXPR)
> > +		    new_stmt
> > +		      = gimple_build_assign (vec_compare, bitop2, new_temp);
> > +		  else
> > +		    new_stmt
> > +		      = gimple_build_assign (vec_compare, bitop2,
> > +					     vec_cond_lhs, new_temp);
> >  		  vect_finish_stmt_generation (vinfo, stmt_info,
> >  					       new_stmt, gsi);
> >  		}
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
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