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Re: [PATCH i386] Allow sibcalls in no-PLT PIC


On Fri, May 15, 2015 at 9:27 AM, Alexander Monakov <amonakov@ispras.ru> wrote:
> Ping?  Any comment about this patch?
>
> On Mon, 4 May 2015, Alexander Monakov wrote:
>
>> With -fno-plt, we don't have to reject even direct calls as sibcall
>> candidates.
>>
>> This patch depends on '-fplt' flag that is introduced in another patch.
>>
>> This patch requires that with -fno-plt all sibcall candidates go through
>> prepare_call_address that transforms the call to a GOT lookup.
>>
>> OK?
>>       * config/i386/i386.c (ix86_function_ok_for_sibcall): Check flag_plt.
>>
>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>> index f29e053..b734350 100644
>> --- a/gcc/config/i386/i386.c
>> +++ b/gcc/config/i386/i386.c
>> @@ -5448,12 +5448,13 @@ ix86_function_ok_for_sibcall (tree decl, tree exp)
>>    /* If we are generating position-independent code, we cannot sibcall
>>       optimize any indirect call, or a direct call to a global function,
>>       as the PLT requires %ebx be live. (Darwin does not have a PLT.)  */
>>    if (!TARGET_MACHO
>>        && !TARGET_64BIT
>>        && flag_pic
>> +      && flag_plt
>>        && (decl && !targetm.binds_local_p (decl)))
>>      return false;
>>
>>    /* If we need to align the outgoing stack, then sibcalling would
>>       unalign the stack, which may break the called function.  */
>>    if (ix86_minimum_incoming_stack_boundary (true)
>>

I think it should be done via psABI change similar to

https://groups.google.com/forum/#!topic/x86-64-abi/n8GYMpqvBxI

which I have implemented on users/hjl/relax branch in binutils.

-- 
H.J.


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