Re: RFC: Avoid calling convert_to_mode with invalid rtl.

[Eric Botcazou <ebotcazou at adacore dot com>]

> 	if (offset)
> 	  {
> 	    machine_mode address_mode;
> 	    rtx offset_rtx = expand_expr (offset, NULL_RTX, VOIDmode,
> 					  EXPAND_SUM);
> 
> 	    gcc_assert (MEM_P (op0));
> 
> 	    address_mode = get_address_mode (op0);
> 	    if (GET_MODE (offset_rtx) != address_mode)
> 	      offset_rtx = convert_to_mode (address_mode, offset_rtx, 0);
> 
>   The problem here is that convert_to_mode() may decide to offload
>   offset_rtx into another reg and then extend the reg to address_mode,
>   but it assumes that offset_rtx is a valid rtl expression for the
>   target.

Note that the very same code is in expand_assignment, so they probably should 
be kept in sync.

>   The patch adds a second call to expand_expr(), giving the address mode
>   as the suggested mode, and using a normal expansion, rather than
>   EXPAND_SUM.  This might work, but even if it does not the rtl in
>   offset_rtx will be valid in a non-address context so that whatever
>   convert_to_mode does will still remain valid.

I don't think that we want to expand twice the same expression.  What about 
calling force_operand on offset_rtx right before convert_to_mode?

-- 
Eric Botcazou