Re: Enable EBX for x86 in 32bits PIC code

[Jeff Law <law@redhat.com>]

On 08/28/14 02:37, Ilya Enkovich 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.
It doesn't really need to be an argument in the traditional sense and 
adding it just complicates things with a target implementation detail as 
far as I can see.

I think you'll find that if you have the call pattern emit a copy from 
pic_offset_table_rtx into EBX and attach of use of EBX to the call then 
most of the code you've written to add the implicit argument just 
disappears.

jeff