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

[Andrew Pinski <pinskia at gmail dot com>]

On Wed, Jun 26, 2013 at 3:39 PM, 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?


IA64-hpux also uses Pmode != ptr_mode, can you provide the testcase
which fails without this change?
I used a powerpc64 target where Pmode != ptr_mode which did not hit
this bug either.

Thanks,
Andrew

>
> Thanks,
> Yufeng
>
>
> gcc/
>         * function.c (assign_parm_find_data_types): Set passed_mode and
>         nominal_mode to the TYPE_MODE of nominal_type for the built
>         pointer type in case of the struct-pass-by-reference.