Richard Biener <rguent...@suse.de> writes:
> On Wed, 12 Jan 2022, Andre Vieira (lists) wrote:
>
>> Hi,
>>
>> This a fix for the regression caused by '[vect] Re-analyze all modes for
>> epilogues'. The earlier patch assumed there was always at least one other
>> mode
>> than VOIDmode, but that does not need to be the case.
>> If we are dealing with a target that does not define more modes for
>> 'autovectorize_vector_modes', the behaviour before the patch would be to try
>> to create an epilogue for the same autodetected_vector_mode, which unless the
>> target supported partial vectors would always fail. So as a fix I suggest
>> trying to vectorize the epilogue with the preferred_simd_mode for QI,
>> mimicking autovectorize_vector_mode, which will be skipped if it is not a
>> vector_mode (since that already should indicate partial vectors aren't
>> possible) or if no partial vectors are supported and its pessimistic NUNITS
>> is
>> larger than the main loop's VF.
>>
>> Currently bootstrapping and regression testing, otherwise OK for trunk? Can
>> someone verify this fixes the issue for PR103971 on powerpc?
>
> Why not simply start at mode_i = 0 which means autodetecting the mode
> to use for the epilogue? That appears to be a much simpler solution to
> me, including for targets where there are more than one element in the
> vector.
VOIDmode doesn't tell us anything about what the autodetected mode
will be, so current short-circuit:
/* If the target does not support partial vectors we can shorten the
number of modes to analyze for the epilogue as we know we can't pick a
mode that has at least as many NUNITS as the main loop's vectorization
factor, since that would imply the epilogue's vectorization factor
would be at least as high as the main loop's and we would be
vectorizing for more scalar iterations than there would be left. */
if (!supports_partial_vectors
&& maybe_ge (GET_MODE_NUNITS (vector_modes[mode_i]), first_vinfo_vf))
{
mode_i++;
if (mode_i == vector_modes.length ())
break;
continue;
}
wouldn't be effective.
Thanks,
Richard
