loongarch gas resolving constant expressions

[Lulu Cai]

On 4/16/25 1:14 PM, Alan Modra wrote:
> The test added in commit 4fe96ddaf614 results in an asan complaint:
> loongarch-parse.y:225:16: runtime error: left shift of negative value -1
> To avoid the complaint, perform left shifts as unsigned (which gives
> the same result on 2's complement machines).  Do the same for
> addition, subtraction and multiplication.  Furthermore, warn on
> divide/modulus by zero.
>
> OK?

We think it's OK. Thanks.

> diff --git a/gas/config/loongarch-parse.y b/gas/config/loongarch-parse.y
> index 97055fe42c3..b75040c14b1 100644
> --- a/gas/config/loongarch-parse.y
> +++ b/gas/config/loongarch-parse.y
> @@ -207,29 +207,41 @@ emit_bin (int op)
>         switch (op)
>   	{
>   	case '*':
> -	  opr1 = opr1 * opr2;
> +	  opr1 = (valueT) opr1 * (valueT) opr2;
>   	  break;
>   	case '/':
> -	  opr1 = opr1 / opr2;
> +	  if (opr2 == 0)
> +	    {
> +	      as_warn (_("Divide by zero!"));
> +	      opr1 = 0;
> +	    }
> +	  else
> +	    opr1 = opr1 / opr2;
>   	  break;
>   	case '%':
> -	  opr1 = opr1 % opr2;
> +	  if (opr2 == 0)
> +	    {
> +	      as_warn (_("Divide by zero!"));
> +	      opr1 = 0;
> +	    }
> +	  else
> +	    opr1 = opr1 % opr2;
>   	  break;
>   	case '+':
> -	  opr1 = opr1 + opr2;
> +	  opr1 = (valueT) opr1 + (valueT) opr2;
>   	  break;
>   	case '-':
> -	  opr1 = opr1 - opr2;
> +	  opr1 = (valueT) opr1 - (valueT) opr2;
>   	  break;
>   	case LEFT_OP:
> -	  opr1 = opr1 << opr2;
> +	  opr1 = (valueT) opr1 << opr2;
>   	  break;
>   	case RIGHT_OP:
>   	  if (opr1 < 0)
> -	    as_warn(_("Right shift of negative numbers may be changed "
> -		  "from arithmetic right shift to logical right shift!"));
> -	  /* Algorithm right shift.  */
> -	  opr1 = (offsetT)opr1 >> (offsetT)opr2;
> +	    as_warn (_("Right shift of negative numbers may be changed "
> +		       "from arithmetic right shift to logical right shift!"));
> +	  /* Arithmetic right shift.  */
> +	  opr1 = opr1 >> opr2;
>   	  break;
>   	case '<':
>   	  opr1 = opr1 < opr2;
>