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Re: Enable EBX for x86 in 32bits PIC code


2014-08-28 16:42 GMT+04:00 Uros Bizjak <ubizjak@gmail.com>:
> On Thu, Aug 28, 2014 at 10:37 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>> 2014-08-28 1:39 GMT+04:00 Jeff Law <law@redhat.com>:
>>> On 08/26/14 15:42, Ilya Enkovich wrote:
>>>>
>>>> diff --git a/gcc/calls.c b/gcc/calls.c
>>>> index 4285ec1..85dae6b 100644
>>>> --- a/gcc/calls.c
>>>> +++ b/gcc/calls.c
>>>> @@ -1122,6 +1122,14 @@ initialize_argument_information (int num_actuals
>>>> ATTRIBUTE_UNUSED,
>>>>       call_expr_arg_iterator iter;
>>>>       tree arg;
>>>>
>>>> +    if (targetm.calls.implicit_pic_arg (fndecl ? fndecl : fntype))
>>>> +      {
>>>> +       gcc_assert (pic_offset_table_rtx);
>>>> +       args[j].tree_value = make_tree (ptr_type_node,
>>>> +                                       pic_offset_table_rtx);
>>>> +       j--;
>>>> +      }
>>>> +
>>>>       if (struct_value_addr_value)
>>>>         {
>>>>         args[j].tree_value = struct_value_addr_value;
>>>
>>> So why do you need this?  Can't this be handled in the call/call_value
>>> expanders or what about attaching the use to CALL_INSN_FUNCTION_USAGE from
>>> inside ix86_expand_call?  Basically I'm not seeing the need for another
>>> target hook here.  I think that would significantly simply the patch as
>>> well.
>>
>> GOT base address become an additional implicit arg with EBX relaxed
>> and I handled it as all other args. I can move EBX initialization into
>> ix86_expand_call. Would still need some hint from target to init
>> pic_offset_table_rtx with proper value in the beginning of function
>> expand.
>
> Maybe you can you use get_hard_reg_initial_val for this?

Actually there is no input hard reg holding GOT address.  Currently I
use initialization with ebx with following ebx initialization in
prolog_epilog pass.  But this is a temporary workaround.  It is
inefficient because always uses callee save reg to get GOT address.  I
suppose we should generate pseudo reg for pic_offset_table_rtx and
also set_got with this register as a destination in expand pass.
After register allocation set_got may be transformed into get_pc_thunk
call with proper hard reg.  But some target hook has to be used for
this.

Ilya

>
> Uros.


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