power4 optimization

Hollis Blanchard hollisb at us.ibm.com
Thu Oct 16 03:56:25 EST 2003

On Tuesday, Oct 14, 2003, at 18:08 US/Central, Anton Blanchard wrote:
> It makes sense to optimise for POWER4 in the default kernel. Up until
> recently -mcpu=POWER4 would tune for it but would still run on RS64 and
> Unfortunately the mtcrf optimisation in POWER4 results in an illegal
> instruction on POWER3.

How about the (totally untested) attached patch?

As future CPUs gain their own gcc optimizations it should turn into a
Kconfig "choice", but this will work for now...

1. what version of gcc started using the mtcrf optimization?
2. do RS64 CPUs support mtcrf?
3. what is the marketing name for RS64? :) (for the Kconfig help text)

Hollis Blanchard
IBM Linux Technology Center
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