Re: memset and host char requirement

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, Jul 26, 2012 at 2:11 PM, Paulo J. Matos <paulo@matos-sorge.com> wrote:
> Hi,
>
> My target has 16bit chars.
> What I am seeing is that in a memset call, the call is not inlined by GCC
> whenever fill value is bigger than host char.
>
> This seems to be due to the code (GCC 4.6.5) in target_char_cast
> (builtins.c), called from expand_builtin_memset_args:
>
> static int
> target_char_cast (tree cst, char *p)
> {
>   unsigned HOST_WIDE_INT val, hostval;
>
>   if (TREE_CODE (cst) != INTEGER_CST
>       || CHAR_TYPE_SIZE > HOST_BITS_PER_WIDE_INT)
>     return 1;
>
>   val = TREE_INT_CST_LOW (cst);
>   if (CHAR_TYPE_SIZE < HOST_BITS_PER_WIDE_INT)
>     val &= (((unsigned HOST_WIDE_INT) 1) << CHAR_TYPE_SIZE) - 1;
>
>   hostval = val;
>   if (HOST_BITS_PER_CHAR < HOST_BITS_PER_WIDE_INT)
>     hostval &= (((unsigned HOST_WIDE_INT) 1) << HOST_BITS_PER_CHAR) - 1;
>
>   if (val != hostval)
>     return 1;
>
>   *p = hostval;
>   return 0;
> }
>
>
> This requires the tree cst variable to fit in target char (which makes
> sense) and in host char (which doesn't make sense).
>
> Why would the fill value in a memset call be required to fit in a host char?

Obviously because of the implementation detail of its caller.

Richard.

> Cheers,
>
> --
> PMatos
>
>