[RFC][PATCH][X86_64] Eliminate PLT stubs for specified external functions via -fno-plt=

[H.J. Lu]

On Thu, May 28, 2015 at 1:54 PM, Sriraman Tallam <tmsriram@google.com> wrote:
> On Thu, May 28, 2015 at 12:05 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Thu, May 28, 2015 at 11:50 AM, Sriraman Tallam <tmsriram@google.com> wrote:
>>> On Thu, May 28, 2015 at 11:42 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Thu, May 28, 2015 at 11:34 AM, Sriraman Tallam <tmsriram@google.com> wrote:
>>>>> I have attached a patch that adds the new attribute "noplt".  Please review.
>>>>>
>>>>> * config/i386/i386.c (avoid_plt_to_call): New function.
>>>>> (ix86_output_call_insn): Generate indirect call for functions
>>>>> marked with "noplt" attribute.
>>>>> (attribute_spec ix86_attribute_): Define new attribute "noplt".
>>>>> * doc/extend.texi: Document new attribute "noplt".
>>>>> * gcc.target/i386/noplt-1.c: New testcase.
>>>>> * gcc.target/i386/noplt-2.c: New testcase.
>>>>>
>>>>
>>>> 2 comments:
>>>>
>>>> 1. Don't remove "%!" prefix before call/jmp.  It is needed for MPX.
>>>> 2. Don't you need to check
>>>>
>>>>       && !TARGET_MACHO
>>>>       && !TARGET_SEH
>>>>       && !TARGET_PECOFF
>>>>
>>>> since it only works for ELF.
>>>
>>> Ok, I will make this change. OTOH, is it just better to piggy-back on
>>> existing -fno-plt change by Alex in calls.c
>>> and do this:
>>>
>>> Index: calls.c
>>> ===================================================================
>>> --- calls.c (revision 223720)
>>> +++ calls.c (working copy)
>>> @@ -226,9 +226,11 @@ prepare_call_address (tree fndecl_or_type, rtx fun
>>>         && targetm.small_register_classes_for_mode_p (FUNCTION_MODE))
>>>        ? force_not_mem (memory_address (FUNCTION_MODE, funexp))
>>>        : memory_address (FUNCTION_MODE, funexp));
>>> -  else if (flag_pic && !flag_plt && fndecl_or_type
>>> +  else if (fndecl_or_type
>>>     && TREE_CODE (fndecl_or_type) == FUNCTION_DECL
>>> -   && !targetm.binds_local_p (fndecl_or_type))
>>> +   && !targetm.binds_local_p (fndecl_or_type)
>>> +   && ((flag_pic && !flag_plt)
>>> +       || (lookup_attribute ("noplt", DECL_ATTRIBUTES(fndecl_or_type)))))
>>>      {
>>>        funexp = force_reg (Pmode, funexp);
>>>      }
>>>
>>
>> Does it work on non-PIC calls?
>
> You are right, it doesnt work.  I have attached the patch with the
> changes you mentioned.
>

Since direct_p is true, do wee need

+  if (GET_CODE (call_op) != SYMBOL_REF
+      || SYMBOL_REF_LOCAL_P (call_op))
+    return false;

H.J.