Re: [PR55547] fix alias regression on alpha on misaligned symbols

[Richard Henderson <rth at redhat dot com>]

On 01/15/2013 08:29 PM, Alexandre Oliva wrote:
>     if (rtx_equal_for_memref_p (x, y))
>       {
> -      if (xsize <= 0 || ysize <= 0)
> +      if (xsize == 0 || ysize == 0)
>   	return 1;
> -      if (c >= 0 && xsize > c)
> +      if (c >= 0 && abs (xsize) - c > 0)
>   	return 1;
> -      if (c < 0 && ysize+c > 0)
> +      if (c < 0 && abs (ysize) + c > 0)
>   	return 1;
>         return 0;
>       }
> @@ -2063,7 +2063,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c)
>   	  y0 = canon_rtx (XEXP (y, 0));
>   	  if (rtx_equal_for_memref_p (x0, y0))
>   	    return (xsize == 0 || ysize == 0
> -		    || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
> +		    || (c >= 0 && abs (xsize) - c > 0)
> +		    || (c < 0 && abs (ysize) + c > 0));
>
>   	  /* Can't properly adjust our sizes.  */
>   	  if (!CONST_INT_P (x1))
> @@ -2119,8 +2120,9 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c)
>         if (CONST_INT_P (x) && CONST_INT_P (y))
>   	{
>   	  c += (INTVAL (y) - INTVAL (x));
> -	  return (xsize <= 0 || ysize <= 0
> -		  || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
> +	  return (xsize == 0 || ysize == 0
> +		  || (c >= 0 && abs (xsize) - c > 0)
> +		  || (c < 0 && abs (ysize) + c > 0));
>   	}

I notice that these expressions (including the first hunk that uses ifs) 
are now all the same. It would seem extremely prudent to pull this out 
to a function so that they stay the same.

That said, I question the change of <= to == 0.  If negative, we don't 
know how much overlap there is as far as I can see.


>         if (GET_CODE (x) == CONST)
> @@ -2139,7 +2141,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y, HOST_WIDE_INT c)
>         if (CONSTANT_P (y))
>   	return (xsize <= 0 || ysize <= 0
>   		|| (rtx_equal_for_memref_p (x, y)
> -		    && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0))));
> +		    && ((c >= 0 && abs (xsize) - c > 0)
> +			|| (c < 0 && abs (ysize) + c > 0))));

This hunk is not needed, as we begin by eliminating <= 0.  So the abs is 
certain to do nothing.


r~