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Re: [CPROG] gcc og 686 optimering



>>>>> "Martin" == Martin Egholm Nielsen <sslug@sslug> writes:

 Martin> Hejsa, Hvordan er det lige man kompilerer specifikt til 686
 Martin> arkitekturen med g++?

Fra info libc:

Intel 386 Options
-----------------

   These `-m' options are defined for the i386 family of computers:

`-mcpu=CPU-TYPE'
     Assume the defaults for the machine type CPU-TYPE when scheduling
     instructions.  The choices for CPU-TYPE are `i386', `i486',
     `i586', `i686', `pentium', `pentiumpro', `k6', and `athlon'

     While picking a specific CPU-TYPE will schedule things
     appropriately for that particular chip, the compiler will not
     generate any code that does not run on the i386 without the
     `-march=CPU-TYPE' option being used.  `i586' is equivalent to
     `pentium' and `i686' is equivalent to `pentiumpro'.  `k6' is the
     AMD chip as opposed to the Intel ones.

`-march=CPU-TYPE'
     Generate instructions for the machine type CPU-TYPE.  The choices
     for CPU-TYPE are the same as for `-mcpu'.  Moreover, specifying
     `-march=CPU-TYPE' implies `-mcpu=CPU-TYPE'.

Dvs det er en --march=i686 du skal have fat i. Grunden til at der både
er en mcpu og en march er at mcpu kun schedulerer instruktionerne så
de passer bedste muligt til den pågældende arkitektur, dvs du kan
stadig kører programmerne på mindre maskiner, hvorimod march (kan)
bruge arkitekturspecifikke instruktioner der ikke findes på andre
(ældre) arkitekturer.

-- 
Bye, Peter Korsgaard


 
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