Code optimization <LEA Instruction>

[Richard B. Johnson]

On Thu, 27 Jan 2000, Alan Cox wrote:

> > One of the things it states is that the LEA instruction can
> > be used to change the value of an index register faster than
> > using the ADD instruction (Page G-10, Intel '486 Rag).
> 
> It is

It is not. Never was and can't possibly be. Further, tests show
as expected, that address generation takes more time than register
addition.

> > 
> > As usual, the Intel reference manual is wrong for all types
> > of CPUs that I have tested (486-686).
> 
> Your test is wrong. See the notes on address generation stalls
> 

Yea. Sure.

Cheers,
Dick Johnson

Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).


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