Tamar Christina <tamar.christ...@arm.com> writes:
> Hi,
>
>> Richard Sandiford <richard.sandif...@arm.com> writes:
>> >> @@ -992,21 +1029,27 @@ vect_recog_dot_prod_pattern (vec_info
>> *vinfo,
>> >> /* FORNOW. Can continue analyzing the def-use chain when this stmt in
>> a phi
>> >> inside the loop (in case we are analyzing an outer-loop). */
>> >> vect_unpromoted_value unprom0[2];
>> >> + enum optab_subtype subtype = optab_vector;
>> >> if (!vect_widened_op_tree (vinfo, mult_vinfo, MULT_EXPR,
>> WIDEN_MULT_EXPR,
>> >> - false, 2, unprom0, &half_type))
>> >> + false, 2, unprom0, &half_type, &subtype))
>> >> + return NULL;
>> >> +
>> >> + if (subtype == optab_vector_mixed_sign
>> >> + && TYPE_UNSIGNED (unprom_mult.type)
>> >> + && TYPE_PRECISION (half_type) * 4 > TYPE_PRECISION
>> >> + (unprom_mult.type))
>> >> return NULL;
>> >
>> > Isn't the final condition here instead that TYPE1 is narrower than TYPE2?
>> > I.e. we need to reject the case in which we multiply a signed and an
>> > unsigned value to get a (logically) signed result, but then
>> > zero-extend it (rather than sign-extend it) to the precision of the
>> > addition.
>> >
>> > That would make the test:
>> >
>> > if (subtype == optab_vector_mixed_sign
>> > && TYPE_UNSIGNED (unprom_mult.type)
>> > && TYPE_PRECISION (unprom_mult.type) < TYPE_PRECISION (type))
>> > return NULL;
>> >
>> > instead.
>>
>> And folding that into the existing test gives:
>>
>> /* If there are two widening operations, make sure they agree on the sign
>> of the extension. The result of an optab_vector_mixed_sign operation
>> is signed; otherwise, the result has the same sign as the operands. */
>> if (TYPE_PRECISION (unprom_mult.type) != TYPE_PRECISION (type)
>> && (subtype == optab_vector_mixed_sign
>> ? TYPE_UNSIGNED (unprom_mult.type)
>> : TYPE_SIGN (unprom_mult.type) != TYPE_SIGN (half_type)))
>> return NULL;
>>
>
> I went with the first one which doesn't add the extra constraints for the
> normal dotproduct as that makes it too restrictive. It's the type of the
> multiplication that determines the operation so dotproduct can be used
> a bit more than where we currently do.
>
> This was relaxed in an earlier patch.
I didn't mean that we should add extra constraints to the normal case
though. The existing test I was referring to above was:
/* If there are two widening operations, make sure they agree on
the sign of the extension. */
if (TYPE_PRECISION (unprom_mult.type) != TYPE_PRECISION (type)
&& TYPE_SIGN (unprom_mult.type) != TYPE_SIGN (half_type))
return NULL;
Although this existing test makes sense for the normal case, IMO testing
TYPE_SIGN (half_type) doesn't make sense for the mixed-sign case. I think
we should therefore replace the existing test with:
/* If there are two widening operations, make sure they agree on the sign
of the extension. The result of an optab_vector_mixed_sign operation
is signed; otherwise, the result has the same sign as the operands. */
if (TYPE_PRECISION (unprom_mult.type) != TYPE_PRECISION (type)
&& (subtype == optab_vector_mixed_sign
? TYPE_UNSIGNED (unprom_mult.type)
: TYPE_SIGN (unprom_mult.type) != TYPE_SIGN (half_type)))
return NULL;
rather than add a separate condition for the mixed-sign case.
The behaviour of the normal case is the same both ways.
Thanks,
Richard
