Re: [PATCH] Fix PR target/103100 -mstrict-align and memset on not aligned buffers

[Richard Sandiford <richard.sandiford@arm.com>]

apinski--- via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> From: Andrew Pinski <apinski@marvell.com>
>
> The problem here is with -mstrict-align, aarch64_expand_setmem needs
> to check the alginment of the mode to make sure we can use it for
> doing the stores.
>
> gcc/ChangeLog:
>
> 	PR target/103100
> 	* config/aarch64/aarch64.c (aarch64_expand_setmem):
> 	Add check for alignment of the mode if STRICT_ALIGNMENT is true.
> ---
>  gcc/config/aarch64/aarch64.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index fdf05505846..2c00583e12c 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -23738,7 +23738,9 @@ aarch64_expand_setmem (rtx *operands)
>  	 over writing.  */
>        opt_scalar_int_mode mode_iter;
>        FOR_EACH_MODE_IN_CLASS (mode_iter, MODE_INT)
> -	if (GET_MODE_BITSIZE (mode_iter.require ()) <= MIN (n, copy_limit))
> +	if (GET_MODE_BITSIZE (mode_iter.require ()) <= MIN (n, copy_limit)
> +	    && (!STRICT_ALIGNMENT
> +		|| MEM_ALIGN (dst) >= GET_MODE_ALIGNMENT (mode_iter.require ())))

Sorry for the slow review.  I think instead we should have keep
track of the alignment of the start byte.  This will be MEM_ALIGN
for the first iteration but could decrease after writing some bytes.

The net effect should be the same in practice.  It just seems
more robust.

Thanks,
Richard

>  	  cur_mode = mode_iter.require ();
>  
>        gcc_assert (cur_mode != BLKmode);