K6 patches for review

[Joern Rennecke]

>   > scheme, now for FPU code Haifa gets quad issue often.  ADJUST_COST is
>   > yet another hack that doesn't work at all...
> I'd argue with "doesn't work at all...".   It's value as diminished
> over time as superscalar machines have become popular.

It is crucial to note that while you can adjust a cost downwards, adjusting
it upwards doesn't work.  So if you have an exception where a cost is higher,
you have to set the default cost to the higher value, and use ADJUST_COST
to lower it in the non-exceptional case.