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gcc flags: differences between (mcpu=)7450 and G4
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panzerdampf
n00b
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Joined: 03 May 2003
Posts: 25
Location: Germany / Dresden

PostPosted: Tue Sep 28, 2004 9:41 am    Post subject: gcc flags: differences between (mcpu=)7450 and G4 Reply with quote

Today I saw G4 as a cpu-type in the gcc-manpage. Till now, I'm using 7450.

So does anyone know the differences between 7450 and G4?
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toojays
Apprentice
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Joined: 21 Jul 2002
Posts: 150
Location: Adelaide, Australia

PostPosted: Tue Sep 28, 2004 10:50 am    Post subject: Reply with quote

G4 is actually equivalent to 7400. mpcu=7450 is for what Motorola used to call G4e (or G4+ or something). Check the Moto or Freescale websites for more info, but I know the G4e has a slightly different pipeline; it may have a different number of functional units as well.

Code compiled with either switch will work on any G4, but one will be tweaked better for the specific CPU. My advice would be to try both and benchmark for yourself.
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_savage
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Joined: 06 Jun 2004
Posts: 308
Location: Redmond, WA

PostPosted: Thu Sep 30, 2004 4:49 pm    Post subject: Reply with quote

Beware of the gcc version though! The G4 flag was introduced with 3.4 and previous releases don't know it. So if you're compiling with 3.3- then sooner or later one of your builds will fail due to an unknown -mcpu flag.
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