Re: [PATCH][AArch64] Improve legitimize_address

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 06/09/16 14:14, Wilco Dijkstra wrote:
> Improve aarch64_legitimize_address - avoid splitting the offset if it is
> supported.  When we do split, take the mode size into account.  BLKmode
> falls into the unaligned case but should be treated like LDP/STP.
> This improves codesize slightly due to fewer base address calculations:
> 
> int f(int *p) { return p[5000] + p[7000]; }
> 
> Now generates:
> 
> f:
> 	add	x0, x0, 16384
> 	ldr	w1, [x0, 3616]
> 	ldr	w0, [x0, 11616]
> 	add	w0, w1, w0
> 	ret
> 
> instead of:
> 
> f:
> 	add	x1, x0, 16384
> 	add	x0, x0, 24576
> 	ldr	w1, [x1, 3616]
> 	ldr	w0, [x0, 3424]
> 	add	w0, w1, w0
> 	ret
> 
> OK for trunk?
> 
> ChangeLog:
> 2016-09-06  Wilco Dijkstra  <wdijkstr@arm.com>
> 
>     gcc/
> 	* config/aarch64/aarch64.c (aarch64_legitimize_address):
> 	Avoid use of base_offset if offset already in range.

OK.

R.

> --
> 
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 27bbdbad8cddc576f9ed4fd0670116bd6d318412..119ff0aecb0c9f88899fa141b2c7f9158281f9c3 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -5058,9 +5058,19 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
>        /* For offsets aren't a multiple of the access size, the limit is
>  	 -256...255.  */
>        else if (offset & (GET_MODE_SIZE (mode) - 1))
> -	base_offset = (offset + 0x100) & ~0x1ff;
> +	{
> +	  base_offset = (offset + 0x100) & ~0x1ff;
> +
> +	  /* BLKmode typically uses LDP of X-registers.  */
> +	  if (mode == BLKmode)
> +	    base_offset = (offset + 512) & ~0x3ff;
> +	}
> +      /* Small negative offsets are supported.  */
> +      else if (IN_RANGE (offset, -256, 0))
> +	base_offset = 0;
> +      /* Use 12-bit offset by access size.  */
>        else
> -	base_offset = offset & ~0xfff;
> +	base_offset = offset & (~0xfff * GET_MODE_SIZE (mode));
>  
>        if (base_offset != 0)
>  	{
>