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From
SubjectRe: NOP instruction
Date
Followup to:  <199812151439.PAA01120@Eris.it>
By author: Caffeina et Nutella <lomarcan@tin.it>
In newsgroup: linux.dev.kernel
>
> XCHG AX, AX (opcode 0x90) was used as a synonym of NOP (NOP was/is
> accepted as NOP -- at least by TASM and is assembled as XCHG AX,AX)
> XCHG doesn't set flags so it's good
>
> BUT, something should be wrong in my manual: XCHG is rated for 3 clock
> ticks on a 486 (Pentium weren't invented yet...) but his 'synonym' NOP
> is rated for only 1 tick....
>

Long time has passed since the 8086. Don't be surprised if some of
the x86 series chips optimize NOP.

-hpa
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