argument of alloca in terms of units or not

[Richard Guenther]

On Thu, Sep 29, 2011 at 5:57 PM, Tom de Vries <Tom_deVries@mentor.com> wrote:
> Richard,
>
> in gimplify_vla_decl, the alloca argument seems to be the size of the vla in units:
> ...
>  t = build_call_expr (t, 1, DECL_SIZE_UNIT (decl));
> ...
>
> I wonder why we are going through this 8 vs. BITS_PER_UNIT conversion here:
> ...
>  elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
>  n_elem = size * 8 / BITS_PER_UNIT;
>  align = MIN (size * 8, BIGGEST_ALIGNMENT);
> ...
> The element size is BITS_PER_UNIT, so 1 unit, and size is in units.

No, the size is in bytes and the gimplify code lacks the conversion.

Richard.

>
> Shouldn't this be:
> ...
> Index: tree-ssa-ccp.c
> ===================================================================
> --- tree-ssa-ccp.c (revision 179210)
> +++ tree-ssa-ccp.c (working copy)
> @@ -1722,8 +1722,8 @@ fold_builtin_alloca_for_var (gimple stmt
>
>   /* Declare array.  */
>   elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
> -  n_elem = size * 8 / BITS_PER_UNIT;
> -  align = MIN (size * 8, BIGGEST_ALIGNMENT);
> +  n_elem = size;
> +  align = MIN (size * BITS_PER_UNIT, BIGGEST_ALIGNMENT);
>   if (align < BITS_PER_UNIT)
>     align = BITS_PER_UNIT;
>   array_type = build_array_type_nelts (elem_type, n_elem);
> ...
>
> Thanks,
> - Tom
>