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

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

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
>
> ;; 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
>

Here is a different approach.  It uses UNSPEC for 8bit divmod.
The generated code is the same.


-- 
H.J.
---
gcc/

2010-06-22  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/44588
	* config/i386/i386.md (UNSPEC_DIVQI): New.
	(UNSPEC_UDIVQI): Likewise.
	(extend_code): Likewise.
	(extract_code): Likewise.
	(*movqi_extzv_3): Likewise.
	(*movqi_extzv_3_rex64): Likewise.
	(<u>divmodqi4): Likewise.
	(*divqi3): Likewise.
	(*udivqi3): Likewise.
	(<u>divqi3): Remvoved.

gcc/testsuite/

2010-06-22  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/44588
	* gcc.target/i386/umod-1.c: New.
	* gcc.target/i386/umod-2.c: Likewise.
	* gcc.target/i386/umod-3.c: Likewise.

Attachment: gcc-pr44588-8.patch
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