discouraging register use

[DJ Delorie]

> > >   [(set (match_operand:SI 0 "" "c,c,?m,?m")
> > >         (plus:SI (match_operand:SI 1 "" "0,0,0,0")
> > > 		 (match_operand:SI 1 "" "c,?m,c,?m")))]
> > 
> > Yes, that looks plausible.  The other way isn't going to work because
> > you penalize c at the same time as m by using "?cm".
> > 
> > Does it actually work?
> 
> One case I tried seems to work,

I found out a seemingly fundamental breakage for this.

In reload.c, we read:

      /* If this alternative can be made to work by reloading,
	 and it needs less reloading than the others checked so far,
	 record it as the chosen goal for reloading.  */

Apparently, if reloading is needed, ONE alternative is chosen, and
reload tries to make it work.  If it fails, there doesn't seem to be a
mechanism for trying other alternatives to see if they work.  Am I
reading this right?