Re: PATCH: PR target/44588: Very inefficient 8bit mod/div

["H.J. Lu" <hjl.tools@gmail.com>]

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

;; Divide AX by r/m8, with result stored in
;; AL <- Quotient
;; AH <- Remainder
(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")))
   (clobber (reg:CC FLAGS_REG))]
  "TARGET_QIMODE_MATH"
  "<sgnprefix>div{b}\t%2"
  [(set_attr "type" "idiv")
   (set_attr "mode" "QI")])

and use

;; Used to extract remainder from AH by 8bit divmod.  Use unspec so
;; that we can extract it from AL.
(define_insn "*movqi_extzh"
  [(set (match_operand:QI 0 "nonimmediate_operand" "=Qm,?R")
        (unspec:QI [(match_operand 1 "register_operand" "Q,Q")]
                   UNSPEC_MOVQI_EXTZH))]

to extract it from AL



-- 
H.J.