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Re: PATCH: PR target/44588: Very inefficient 8bit mod/div
On Wed, Jun 23, 2010 at 3:39 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
> On 06/24/2010 12:01 AM, H.J. Lu wrote:
>>
>> On Wed, Jun 23, 2010 at 2:22 PM, H.J. Lu<hjl.tools@gmail.com> ?wrote:
>>>
>>> On Wed, Jun 23, 2010 at 12:50 PM, H.J. Lu<hjl.tools@gmail.com> ?wrote:
>>>>
>>>> On Wed, Jun 23, 2010 at 12:36 PM, Paolo Bonzini<bonzini@gnu.org> ?wrote:
>>>>>
>>>>> On 06/23/2010 09:35 PM, H.J. Lu wrote:
>>>>>>
>>>>>> On Wed, Jun 23, 2010 at 12:16 PM, Paolo Bonzini<bonzini@gnu.org>
>>>>>> ?wrote:
>>>>>>>
>>>>>>> On 06/23/2010 08:24 PM, H.J. Lu wrote:
>>>>>>>>
>>>>>>>> ?[(set (match_operand:HI 0 "register_operand" "=a")
>>>>>>>> ? ? ? ? (div:HI
>>>>>>>> ? ? ? ? ? (match_operand:HI 1 "register_operand" "0")
>>>>>>>> ? ? ? ? ? (match_operand:QI 2 "nonimmediate_operand" "qm")))
>>>>>>>> ? ?(clobber (reg:CC FLAGS_REG))]
>>>>>>>
>>>>>>> Maybe this:
>>>>>>>
>>>>>>> [(set (match_operand:QI 0 "register_operand" "=a")
>>>>>>> ? (subreg:QI
>>>>>>> ? ?(div:HI
>>>>>>> ? ? (match_operand:HI 1 "register_operand" "0")
>>>>>>> ? ? (match_operand:QI 2 "nonimmediate_operand" "qm")) 0))
>>>>>>> ?(clobber (reg:CC FLAGS_REG))]
>>>>>>>
>>>>>>
>>>>>> It doesn't make a big difference since only lower 8bit
>>>>>> is set by it.
>>>>>
>>>>> For full divmod you have to shift mod and ior of course. ?I understood
>>>>> that
>>>>> you were talking of *<u>divqi3.
>>>>>
>>>>
>>>> I can't do shift/ior on QI output from *<u>divqi3. I have
>>>>
>>> Here is a different approach. ?It uses UNSPEC for 8bit divmod.
>>> The generated code is the same.
>>
>> An updated patch. ?No need for *movqi_extzv_3 and
>> *movqi_extzv_3_rex64.
>
> I don't understand exactly what the problem was; clearly it couldn't work as
> long as this pattern was cheating blatantly:
Upper 8bit registers aren't real registers. You can't
do RA with them.
> (define_insn "*<u>divqi3"
> ?[(set (match_operand:QI 0 "register_operand" "=a")
> ? ? ? ?(any_div:QI
> ? ? ? ? ?(match_operand:HI 1 "register_operand" "0")
> ? ? ? ? ?(match_operand:QI 2 "nonimmediate_operand" "qm")))
>
> Anyway this patch is IMO much nicer than the first ones, so if Uros is okay
> I don't think it's useful to pursue a more accurate representation. ?Just
> make sure that REG_EQUAL notes are added to the two extractions.
>
What are REG_EQUAL notes used for? As far as the
rest of gcc is concerned, there are no upper 8bit
registers. But you can access bits 8-15 of HI, SI,
DI registers via XXX_extract.
--
H.J.