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Re: Better handling for multi-word values?
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?
And Richard replied:
[ Glad am I that thou hast asked this question - oops, wrong track ]
> 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.
I hate to break into this discussion, because I do not really have
studied all the ins and outs of (paradoxical) SUBREGs vs.
MULTIWORDs, but one of the things I *do* want to know is - do we
understand why using [SD]Cmode "registers" leads to far better code
than the Fortran frontend spelling out the complex arithmetic in
[SD]Fmode ?
I.e., do we understand why I see the following phenomenon:
http://www.cygnus.com/ml/egcs-bugs/1998-Apr/0245.html ?
Cheers,
Toon.