[Patch, AArch64, ILP32] 3/5 Minor change in function.c:assign_parm_find_data_types()

[Marcus Shawcroft]

On 26 June 2013 23:39, Yufeng Zhang <Yufeng.Zhang@arm.com> wrote:
> This patch updates assign_parm_find_data_types to assign passed_mode and
> nominal_mode with the mode of the built pointer type instead of the
> hard-coded Pmode in the case of pass-by-reference.  This is in line with the
> assignment to passed_mode and nominal_mode in other cases inside the
> function.
>
> assign_parm_find_data_types generally uses TYPE_MODE to calculate
> passed_mode and nominal_mode:
>
>   /* Find mode of arg as it is passed, and mode of arg as it should be
>      during execution of this function.  */
>   passed_mode = TYPE_MODE (passed_type);
>   nominal_mode = TYPE_MODE (nominal_type);
>
> this includes the case when the passed argument is a pointer by itself.
>
> However there is a discrepancy when it deals with argument passed by
> invisible reference; it builds the argument's corresponding pointer type,
> but sets passed_mode and nominal_mode with Pmode directly.
>
> This is OK for targets where Pmode == ptr_mode, but on AArch64 with ILP32
> they are different with Pmode as DImode and ptr_mode as SImode. When such a
> reference is passed on stack, the reference is prepared by the caller in the
> lower 4 bytes of an 8-byte slot but is fetched by the callee as an 8-byte
> datum, of which the higher 4 bytes may contain junk.  It is probably the
> combination of Pmode != ptr_mode and the particular ABI specification that
> make the AArch64 ILP32 the first target on which the issue manifests itself.
>
> Bootstrapped on x86_64-none-linux-gnu.
>
> OK for the trunk?

Yufeng, this change makes sense to me, however I can't approve such a change.
/Marcus