I've found a bug in the doloop optimization that has to do with how the
Ada front end generates code.  This occurs on PowerPC and Alpha, it
doesn't seem to happen on x86 because this particular optimiation never
seems to get hit.

The problem is that the Ada front end generates code for "for" loops like:

     for I in 1 .. Len loop
         a[i] := b[i];
     end loop;

The output RTL (in pseudocode) is something like:

     I := 1;
     goto loopstart
loopcont:
     i := i + 1;
loopstart:
     a[i] := b[i];
     if (i /= Len) then
         goto loopcont;
     end if;

The doloop optimization doesn't handle this case correctly because the
loop variable is incremented after the loop comparison, not before, so
doloop optimization will execute the loop one too few times.  I've
attached a cheap hack that fixes the bug, but it's a cheap hack.  How
should this really be fixed?

-Corey