Re: [PATCH] Fix expansion issues on type changing MEM_REFs on LHS (PR middle-end/48335)

[Mike Stump <mikestump at comcast dot net>]

On Mar 30, 2011, at 9:05 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> +	  else if (bitpos >= mode_bitsize / 2)
> +	    result = store_field (XEXP (to_rtx, 1), bitsize,
> +				  bitpos - mode_bitsize / 2, mode1, from,
> +				  TREE_TYPE (tem), get_alias_set (to),
> +				  nontemporal);

> -	      gcc_assert (bitpos == 0 || bitpos == GET_MODE_BITSIZE (mode1));
> -	      result = store_expr (from, XEXP (to_rtx, bitpos != 0), false,
> -				   nontemporal);
> +	      rtx temp = assign_stack_temp (GET_MODE (to_rtx),
> +					    GET_MODE_SIZE (GET_MODE (to_rtx)),
> +					    0);
> +	      write_complex_part (temp, XEXP (to_rtx, 0), false);
> +	      write_complex_part (temp, XEXP (to_rtx, 1), true);
> +	      result = store_field (temp, bitsize, bitpos, mode1, from,
> +				    TREE_TYPE (tem), get_alias_set (to),
> +				    nontemporal);
> +	      emit_move_insn (XEXP (to_rtx, 0), read_complex_part (temp, false));
> +	      emit_move_insn (XEXP (to_rtx, 1), read_complex_part (temp, true));

I think this is bad.  I think this patch fixes it.  The problem is that we can't write outside the bounds of the object.  So, instead we punt out of the register case, and instead spill it to memory that _is_ big enough, and then spill it back to registers.  Of course, I'd rather emit a diagnostic when extra is non-zero…  but not sure people yet buy into that around here.

Thoughts?

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