Re: Can't use SImode as Pmode for x32

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Mar 18, 2011 at 3:42 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Fri, Mar 18, 2011 at 03:32:45PM -0700, H.J. Lu wrote:
>> On Fri, Mar 18, 2011 at 3:18 PM, Richard Henderson <rth@redhat.com> wrote:
>> > On 03/18/2011 02:56 PM, H.J. Lu wrote:
>> >> X86 backend uses Pmode for hardware pointer size. Changes
>> >> it to 32bit for x32, which is really 64bit process, breaks many
>> >> assumptions of x86 backend. push/pop/call is just the tip of
>> >> the iceberg.
>> >
>> > Please enumerate "many assumptions". ?I can't think of any off
>> > the top of my head.
>> >
>>
>> I don't have a complete list. ?gen_push is one of them:
>>
>> static rtx
>> gen_push (rtx arg)
>> {
>> ? struct machine_function *m = cfun->machine;
>>
>> ? if (m->fs.cfa_reg == stack_pointer_rtx)
>> ? ? m->fs.cfa_offset += UNITS_PER_WORD;
>> ? m->fs.sp_offset += UNITS_PER_WORD;
>>
>> ? return gen_rtx_SET (VOIDmode,
>> ? ? ? ? ? ? ? ? ? ? ? gen_rtx_MEM (Pmode,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?gen_rtx_PRE_DEC (Pmode,
>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? stack_pointer_rtx)),
>> ? ? ? ? ? ? ? ? ? ? ? arg);
>> }
>>
>> You can only push/pup 64bit in hardware 64bit mode.
>
> That's still push/pop/call. ?And you can certainly use a Pmode (== SImode)
> stack_pointer_rtx to describe it too, push/pop reference %rsp just
> implicitly. ?For the MEM you would just use DImode for x32 in that case,
> or for <= 32 bit pushes you could describe it as a SImode MEM with
> PRE_MODIFY inside of it.

Because TARGET_MEM_REF only works on ptr_mode:

http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00655.html

x32 accepts (%eax,%ebx,4).

> For addresses, you could use 32-bit regs (i.e. addr32 prefix) by default,
> perhaps with machine reorg optimizing away some of the addr32 prefixes when
> it can prove the base register is already zero extended, and if there is no
> added or very small one.

You can change 32bit registers in memory address to 64bit only if there is
no index register.

I will try ptr_mode == SImode and report any new problems.

Thanks.


-- 
H.J.