On Thu, Aug 28, 2014 at 3:29 PM, Ilya Enkovich <enkovich....@gmail.com> 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.
>>
>> Let me expand my idea a bit. IIRC, get_hard_reg_initial_val and
>> friends will automatically emit intialization of a pseudo from
>> pic_offset_table_rtx hard reg. After reload, real initialization of
>> pic_offset_table_rtx hard reg is emitted in pro_and_epilogue pass. I
>> don't know if this works with current implementation of dynamic
>> pic_offset_table_rtx selection, though.
>
> That means you should choose some hard reg early before register
> allocation to be used for PIC reg initialization. I do not like we
> have to do this and want to just generate set_got with pseudo reg and
> do not involve any additional hard reg. That would look like
>
> (insn/f 168 167 169 2 (parallel [
> (set (reg:SI 127)
> (unspec:SI [
> (const_int 0 [0])
> ] UNSPEC_SET_GOT))
> (clobber (reg:CC 17 flags))
> ]) test.cc:42 -1
> (expr_list:REG_CFA_FLUSH_QUEUE (nil)
> (nil)))
>
> after expand pass. r127 is pic_offset_table_rtx here. And after
> reload it would become:
>
> (insn/f 168 167 169 2 (parallel [
> (set (reg:SI 3 bx)
> (unspec:SI [
> (const_int 0 [0])
> ] UNSPEC_SET_GOT))
> (clobber (reg:CC 17 flags))
> ]) test.cc:42 -1
> (expr_list:REG_CFA_FLUSH_QUEUE (nil)
> (nil)))
>
> And no additional actions are required on pro_and_epilogue. Also it
> simplifies analysis whether we should generate set_got at all.
> Current we check hard reg is ever live which is wrong with not fixed
> ebx because any usage of hard reg used to init GOT doesn't mean GOT
> usage. And with my proposed scheme unused GOT would mean DCE just
> removes useless set_got.
Yes this is better. I was under impression you want to retain current
initialization insertion in expand_prologue.
Uros.
