GNU and Freescale MPC83xx / e300 core support?

[Kumar Gala]

On Mar 7, 2006, at 9:54 AM, Russell McGuire wrote:

> Thanks all...
>
> The author of that comment humbly apologizes for his ineptitude on  
> the FPU.
>
> It would appear both cores have the same number of execution units,  
> i.e. 5
> So David, I guess in all this the only real difference seems to be  
> the bus
> architecture, raw clock speed, and perhaps a few new instructions.  
> I checked
> both manuals this morning and they do differ in some small ways.
>
> * 603e, up to 4 instructions in the pipeline, only 3 being complete  
> per
> clock
> * e300, up to 5 instructions in the pipeline, still only 3 being  
> completed
> or start per clock.
> * Add/compare instructions are now executed in the IU unit instead  
> of the
> load/store unit. May be the same, but wasn't specific in earlier 603e
> manuals.
> * One more HID0 bit than G2, ability to interrupt based on cache  
> parity
> error
> * new icbt instruction, instruction cache initialization
>
> So there is a section inside the 8360E manual that outlines the  
> specific
> enhancements. "Features specific to the e300 core not present on  
> the G2
> processors follow:" Page  1-5.
>
> So I guess my question is back up, does anyone know if an optimized  
> compiler
> would offer any noticeable performance enhancements in regards to  
> these
> changes? Other than the obvious instruction being added?

If you are asking about relative performance between the same  
compiler tuned for a 603 vs e300, the there would most likely be a  
small improvement.

However, a few things to note.  The new icbt instruction is really  
intended for hand written assemble code and its highly unlikely that  
a compiler will ever generate it.  Second, the other improvements  
from the base 603e/G2LE in 8280, like doubling of the L1 caches has a  
significant improvement in performance.

- kumar