core changes for mep port

[Julian Brown]

Steven Bosscher wrote:
> All of this feels (to me anyway) like adding a lot of code to the
> middle end to support MEP specific arch features.  I understand it is
> in the mission statement that more ports is a goal for GCC, but I
> wonder if this set of changes is worth the maintenance burden...

FWIW, it sounds to me like this feature may also be useful for current 
iterations of the ARM NEON extension (which we're planning to submit 
support for quite soon). NEON supports various operations on DImode 
quantities, but we don't use them for normal code at present because 
moving values from NEON back to ARM core registers is relatively slow, 
so we want to avoid doing that as far as possible.

So, if there was a way of specifying that a particular value should be 
kept in a NEON register, that'd be a good thing, I think.

Cheers,

Julian