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

[Richard Sandiford <richard.sandiford@arm.com>]

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.

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);
>  		}