Better handling for multi-word values?

[Toon Moene]

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.