Re: [MI400] most efficient RISC instruction

["Larry Loen" <lwloen@xxxxxxxxxx>]

>From Leif Svalgaard:
>From: Dave McKenzie <davemck@zbiggroup.com>
>> Larry's probably thinking of the "with update" family of
>>instructions, e.g.:
>> Load Doubleword with Update Indexed  X-form
>>
>>   ldux    RT,RA,RB
>>
>> EA <- (RA) + (RB)
>> RT <- MEM(EA, 8)
>> RA <- EA
>
>> Let the effective address (EA) be the sum (RA)+(RB).  The doubleword in
>>storage addressed by EA is loaded into RT.
>>
>> EA is placed into register RA.
>>
>> If RA=0 or RA=RT, the instruction form is invalid.

>but this instruction does not increment the pointer in memory.
>If Larry knows about an undocumented instruction, let him tell us.
>Among the documented instructions there are none that updates
>the pointer.

You're reading more than I intended into my earlier response.

I was only trying to object to the idea someone expressed that RISC
architecture couldn't do two relevant things in one instruction.  No more,
no less.  And, for all my faults posting it up, Dave seems to have grasped
what I was up to.



Larry W. Loen  -   Senior Linux, Java, and iSeries Performance Analyst
                          Dept HP4, Rochester MN