Better handling for multi-word values?

Richard Henderson
Tue Sep 8 06:23:00 GMT 1998

On Mon, Sep 07, 1998 at 01:56:37PM -0600, Jeffrey A Law wrote:
> So if concats where extended to handle multiple objects would we be
> able to use them to do the same thing efficiently?
> Or should CONCAT go away after your MULTIWORD changes?

Six the one, half dozen the other.

I'm not sure how much a thing like MULTIWORD buys us, at least
in the context of the DImode bits being discussed here.  It's
basically SUBREGs turned inside out, and would still require
special code in combine and elsewhere to be able to deal with
them effectively.

I'm willing to be proven wrong, but my take on this issue is
that we should just split up multi-word arithmetic entirely into
its constituant parts right from the start, and just deal with
plain ol' REGs.

That said, you and I have before discussed the need for a bit
of RTL that could represent entire structures (holes and all)
so that individual slots could more readily be optimized into
registers etc.  Perhaps the memory optimizations that have been
discussed make this unnecessary, but the less guessing the alias
code has to do, the better.


More information about the Gcc mailing list