Re: [PATCH 9/21]middle-end: implement vectorizable_early_exit for codegen of exit code

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

Richard Biener <rguenther@suse.de> writes:
> On Mon, 11 Dec 2023, Tamar Christina wrote:
>> @@ -5553,6 +5554,83 @@ integer_type_for_mask (tree var, vec_info *vinfo)
>>    return build_nonstandard_integer_type (def_stmt_info->mask_precision, 1);
>>  }
>>  
>> +/* Function vect_recog_gcond_pattern
>> +
>> +   Try to find pattern like following:
>> +
>> +     if (a op b)
>> +
>> +   where operator 'op' is not != and convert it to an adjusted boolean pattern
>> +
>> +     mask = a op b
>> +     if (mask != 0)
>> +
>> +   and set the mask type on MASK.
>> +
>> +   Input:
>> +
>> +   * STMT_VINFO: The stmt at the end from which the pattern
>> +		 search begins, i.e. cast of a bool to
>> +		 an integer type.
>> +
>> +   Output:
>> +
>> +   * TYPE_OUT: The type of the output of this pattern.
>> +
>> +   * Return value: A new stmt that will be used to replace the pattern.  */
>> +
>> +static gimple *
>> +vect_recog_gcond_pattern (vec_info *vinfo,
>> +			 stmt_vec_info stmt_vinfo, tree *type_out)
>> +{
>> +  gimple *last_stmt = STMT_VINFO_STMT (stmt_vinfo);
>> +  gcond* cond = NULL;
>> +  if (!(cond = dyn_cast <gcond *> (last_stmt)))
>> +    return NULL;
>> +
>> +  auto lhs = gimple_cond_lhs (cond);
>> +  auto rhs = gimple_cond_rhs (cond);
>> +  auto code = gimple_cond_code (cond);
>> +
>> +  tree scalar_type = TREE_TYPE (lhs);
>> +  if (VECTOR_TYPE_P (scalar_type))
>> +    return NULL;
>> +
>> +  if (code == NE_EXPR && zerop (rhs))
>
> I think you need && VECT_SCALAR_BOOLEAN_TYPE_P (scalar_type) here,
> an integer != 0 would not be an appropriate mask.  I guess two
> relevant testcases would have an early exit like
>
>    if (here[i] != 0)
>      break;
>
> once with a 'bool here[]' and once with a 'int here[]'.
>
>> +    return NULL;
>> +
>> +  tree vecitype = get_vectype_for_scalar_type (vinfo, scalar_type);
>> +  if (vecitype == NULL_TREE)
>> +    return NULL;
>> +
>> +  /* Build a scalar type for the boolean result that when vectorized matches the
>> +     vector type of the result in size and number of elements.  */
>> +  unsigned prec
>> +    = vector_element_size (tree_to_poly_uint64 (TYPE_SIZE (vecitype)),
>> +			   TYPE_VECTOR_SUBPARTS (vecitype));
>> +
>> +  scalar_type
>> +    = build_nonstandard_integer_type (prec, TYPE_UNSIGNED (scalar_type));
>> +
>> +  vecitype = get_vectype_for_scalar_type (vinfo, scalar_type);
>> +  if (vecitype == NULL_TREE)
>> +    return NULL;
>> +
>> +  tree vectype = truth_type_for (vecitype);
>
> That looks awfully complicated.  I guess one complication is that
> we compute mask_precision & friends before this pattern gets
> recognized.  See vect_determine_mask_precision and its handling
> of tcc_comparison, see also integer_type_for_mask.  For comparisons
> properly handled during pattern recog the vector type is determined
> in vect_get_vector_types_for_stmt via
>
>   else if (vect_use_mask_type_p (stmt_info))
>     {
>       unsigned int precision = stmt_info->mask_precision;
>       scalar_type = build_nonstandard_integer_type (precision, 1);
>       vectype = get_mask_type_for_scalar_type (vinfo, scalar_type, 
> group_size);
>       if (!vectype)
>         return opt_result::failure_at (stmt, "not vectorized: unsupported"
>                                        " data-type %T\n", scalar_type);
>
> Richard, do you have any advice here?  I suppose vect_determine_precisions
> needs to handle the gcond case with bool != 0 somehow and for the
> extra mask producer we add here we have to emulate what it would have 
> done, right?

How about handling gconds directly in vect_determine_mask_precision?
In a sense it's not needed, since gconds are always roots, and so we
could calculate their precision on the fly instead.  But handling it in
vect_determine_mask_precision feels like it should reduce the number
of special cases.

Thanks,
Richard