On 10/25/2016 07:59 PM, David Gibson wrote:
> On Sat, Oct 15, 2016 at 08:37:49PM -0700, Richard Henderson wrote:
>> Use the new primitives for RDWINM and RLDICL.
>>
>> Cc: qemu-...@nongnu.org
>> Signed-off-by: Richard Henderson <r...@twiddle.net>
>> ---
>> target-ppc/translate.c | 9 ++++-----
>> 1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
>> index bfc1301..724d95c 100644
>> --- a/target-ppc/translate.c
>> +++ b/target-ppc/translate.c
>> @@ -1977,9 +1977,8 @@ static void gen_rlwinm(DisasContext *ctx)
>> if (mb == 0 && me == (31 - sh)) {
>> tcg_gen_shli_tl(t_ra, t_rs, sh);
>> tcg_gen_ext32u_tl(t_ra, t_ra);
>> - } else if (sh != 0 && me == 31 && sh == (32 - mb)) {
>> - tcg_gen_ext32u_tl(t_ra, t_rs);
>> - tcg_gen_shri_tl(t_ra, t_ra, mb);
>> + } else if (me == 31 && (me - mb + 1) + sh <= 32) {
>
> I'm having trouble figuring out what the second part of this condition
> is supposed to be checking for, and it seems like it's too
> restrictive.
>
> For example, everything except the LSB of a word would be:
> rlwnim rT,rA,31,1,31
> which would fail the test, but it should be fine to implement that
> with an extract op.
It was confusing to me too, which is why I rearranged this in the v2 of this
patchset. To which thread you also responded yesterday, so...
Anyway, in v2 this looks like
if (sh != 0 && len > 0 && me == (31 - sh)) {
tcg_gen_deposit_z_tl(t_ra, t_rs, sh, len);
} else if (me == 31 && rsh + len <= 32) {
tcg_gen_extract_tl(t_ra, t_rs, rsh, len);
} else {
Basically, we're trying to match those combinations of rotate+mask that can be
implemented with shifts instead of real rotations. That is, the mask doesn't
follow the rotate around the end of the word.
r~
