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Re: Describing multi-register values in RTL
Le jeudi 21 octobre 2010 Ã 21:11 -0700, Ian Lance Taylor a Ãcrit :
> Paul Koning <paul_koning@Dell.com> writes:
>
> > To take that example, on the pdp11 an SImode is two HImodes. Could
> > the RTL template in the MD file for, say, addsi3 split that into two
> > or three insns that operate on HImode values and describe the actual
> > instructions? In this case: add high parts, then add low parts and
> > propagate carry into high. Split that way it would seem you would not
> > be constrained to adjacent registers, or for that matter to both being
> > registers at all.
This is exactly the kind of thing I'm looking at.
> The lower subreg pass will do that for you if you have the right set of
> insns.
Could you expand a bit on what the 'right set of instructions' is or
even better give an example of an md file where we could find an
example?
Thanks a lot!
Fred