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

[Sriraman Tallam]

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);
     }


Thanks
Sri

>
> --
> H.J.