powerpc compare_and_swap fails

[Richard Henderson]

On 11/17/2011 12:37 AM, Alan Modra wrote:
> -      oldval = convert_modes (SImode, mode, oldval, 1);
> +      oldval = gen_reg_rtx (SImode);
> +      convert_move (oldval, orig, 1);
>        oldval = expand_simple_binop (SImode, ASHIFT, oldval, shift,
>  				    oldval, 1, OPTAB_LIB_WIDEN);

Gah.  From convert_modes, oldval is a subreg, and modifying that
subreg gets us into all sorts of trouble.  The fix should be as
simple as 

- 				    oldval, 1, OPTAB_LIB_WIDEN);
+ 				    NULL_RTX, 1, OPTAB_LIB_WIDEN);

so that we don't write back into the subreg.


r~