On 8/25/20 6:43 AM, Peter Maydell wrote:
> On Sat, 15 Aug 2020 at 02:32, Richard Henderson
> <richard.hender...@linaro.org> wrote:
>>
>> Missed out on compressing the second half of a predicate
>> with length vl % 512 > 256.
>>
>> Adjust all of the x + (y << s) to x | (y << s) as a
>> general style fix.
>>
>> Reported-by: Laurent Desnogues <laurent.desnog...@gmail.com>
>> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
>> ---
>> target/arm/sve_helper.c | 30 +++++++++++++++++++++---------
>> 1 file changed, 21 insertions(+), 9 deletions(-)
>>
>> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c
>> index 4758d46f34..fcb46f150f 100644
>> --- a/target/arm/sve_helper.c
>> +++ b/target/arm/sve_helper.c
>> @@ -1938,7 +1938,7 @@ void HELPER(sve_uzp_p)(void *vd, void *vn, void *vm,
>> uint32_t pred_desc)
>> if (oprsz <= 8) {
>> l = compress_bits(n[0] >> odd, esz);
>> h = compress_bits(m[0] >> odd, esz);
>> - d[0] = extract64(l + (h << (4 * oprsz)), 0, 8 * oprsz);
>> + d[0] = l | (h << (4 * oprsz));
>
> Why did we drop the extract64() here ? This doesn't seem
> to correspond to either of the things the commit message
> says we're doing.
Indeed, the commit message could use expansion.
> Also, if oprsz is < 8, don't we need to mask out the high
> bits in l that would otherwise overlap with h << (4 * oprsz) ?
> Are they guaranteed zeroes somehow?
They are guaranteed zeros. See aarch64_sve_narrow_vq.
>> for (i = 0; i < oprsz_16; i++) {
>> l = m[2 * i + 0];
>> h = m[2 * i + 1];
>> l = compress_bits(l >> odd, esz);
>> h = compress_bits(h >> odd, esz);
>> - tmp_m.p[i] = l + (h << 32);
>> + tmp_m.p[i] = l | (h << 32);
>> }
>> - tmp_m.p[i] = compress_bits(m[2 * i] >> odd, esz);
>> + l = m[2 * i + 0];
>> + h = m[2 * i + 1];
>> + l = compress_bits(l >> odd, esz);
>> + h = compress_bits(h >> odd, esz);
>> + tmp_m.p[i] = l | (h << final_shift);
>>
>> swap_memmove(vd + oprsz / 2, &tmp_m, oprsz / 2);
>
> Aren't there cases where the 'n' part of the result doesn't
> end up a whole number of bytes and we have to do a shift as
> well as a byte copy?
No, oprsz will always be a multiple of 2 for predicates.
Just like oprsz will always be a multiple of 16 for sve vectors.
r~
