On Fri, May 29, 2015 at 12:35 PM, Jan Hubicka <hubi...@ucw.cz> wrote:
>> * 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.
>>
>> Index: config/i386/i386.c
>> ===================================================================
>> --- config/i386/i386.c (revision 223720)
>> +++ config/i386/i386.c (working copy)
>> @@ -25599,6 +25599,24 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx call
>> return call;
>> }
>>
>> +/* Return true if the function being called was marked with attribute
>> + "noplt". If this function is defined, this should return false. */
>> +static bool
>> +avoid_plt_to_call (rtx call_op)
>> +{
>> + if (SYMBOL_REF_LOCAL_P (call_op))
>> + return false;
>> +
>> + tree symbol_decl = SYMBOL_REF_DECL (call_op);
>> +
>> + if (symbol_decl != NULL_TREE
>> + && TREE_CODE (symbol_decl) == FUNCTION_DECL
>> + && lookup_attribute ("noplt", DECL_ATTRIBUTES (symbol_decl)))
>> + return true;
>> +
>> + return false;
>> +}
>
> OK, now we have __attribute__ (optimize("noplt")) which binds to the caller
> and makes
> all calls in the function to skip PLT and __attribute__ ("noplt") which binds
> to callee
> and makes all calls to function to not use PLT.
>
> That sort of makes sense to me, but why "noplt" attribute is not implemented
> at generic level
> just like -fplt? Is it only because every target supporting PLT would need
> update in its
> call expansion patterns?
Yes, that is what I had in mind.
>
> Also I think the PLT calls have EBX in call fusage wich is added by
> ix86_expand_call.
> else
> {
> /* Static functions and indirect calls don't need the pic register. */
> if (flag_pic
> && (!TARGET_64BIT
> || (ix86_cmodel == CM_LARGE_PIC
> && DEFAULT_ABI != MS_ABI))
> && GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF
> && ! SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0)))
> {
> use_reg (&use, gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM));
> if (ix86_use_pseudo_pic_reg ())
> emit_move_insn (gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM),
> pic_offset_table_rtx);
> }
>
> I think you want to take that away from FUSAGE there just like we do for
> local calls
> (and in fact the code should already check flag_pic && flag_plt I suppose.
Done that now and patch attached.
Thanks
Sri
>
> Honza
* config/i386/i386.c (avoid_plt_to_call): New function.
(ix86_expand_call): Dont use the PIC register when external function
calls are not made via PLT.
(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.
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c (revision 223720)
+++ config/i386/i386.c (working copy)
@@ -25475,6 +25475,28 @@ construct_plt_address (rtx symbol)
return tmp;
}
+/* Return true if the function being called was marked with attribute
+ "noplt". If this function is defined, this should return false. This
+ is currently used only with 64-bit ELF targets. */
+static bool
+avoid_plt_to_call (rtx call_op)
+{
+ if (!TARGET_64BIT || TARGET_MACHO|| TARGET_SEH || TARGET_PECOFF)
+ return false;
+
+ if (SYMBOL_REF_LOCAL_P (call_op))
+ return false;
+
+ tree symbol_decl = SYMBOL_REF_DECL (call_op);
+
+ if (symbol_decl != NULL_TREE
+ && TREE_CODE (symbol_decl) == FUNCTION_DECL
+ && lookup_attribute ("noplt", DECL_ATTRIBUTES (symbol_decl)))
+ return true;
+
+ return false;
+}
+
rtx
ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
rtx callarg2,
@@ -25497,13 +25519,16 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx call
}
else
{
- /* Static functions and indirect calls don't need the pic register. */
+ /* Static functions and indirect calls don't need the pic register.
Also,
+ check if PLT was explicitly avoided via no-plt or "noplt" attribute,
making
+ it an indirect call. */
if (flag_pic
&& (!TARGET_64BIT
|| (ix86_cmodel == CM_LARGE_PIC
&& DEFAULT_ABI != MS_ABI))
&& GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF
- && ! SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0)))
+ && ! SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0))
+ && flag_plt && !avoid_plt_to_call (XEXP (fnaddr, 0)))
{
use_reg (&use, gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM));
if (ix86_use_pseudo_pic_reg ())
@@ -25611,7 +25636,13 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op
if (SIBLING_CALL_P (insn))
{
if (direct_p)
- xasm = "%!jmp\t%P0";
+ {
+ if (!TARGET_MACHO && !TARGET_SEH && !TARGET_PECOFF
+ && TARGET_64BIT && avoid_plt_to_call (call_op))
+ xasm = "%!jmp\t*%p0@GOTPCREL(%%rip)";
+ else
+ xasm = "%!jmp\t%P0";
+ }
/* SEH epilogue detection requires the indirect branch case
to include REX.W. */
else if (TARGET_SEH)
@@ -25654,7 +25685,13 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op
}
if (direct_p)
- xasm = "%!call\t%P0";
+ {
+ if (!TARGET_MACHO && !TARGET_SEH && !TARGET_PECOFF
+ && TARGET_64BIT && avoid_plt_to_call (call_op))
+ xasm = "%!call\t*%p0@GOTPCREL(%%rip)";
+ else
+ xasm = "%!call\t%P0";
+ }
else
xasm = "%!call\t%A0";
@@ -46628,6 +46665,9 @@ static const struct attribute_spec ix86_attribute_
false },
{ "callee_pop_aggregate_return", 1, 1, false, true, true,
ix86_handle_callee_pop_aggregate_return, true },
+ /* Attribute to avoid calling function via PLT. */
+ { "noplt", 0, 0, true, false, false, ix86_handle_fndecl_attribute,
+ false },
/* End element. */
{ NULL, 0, 0, false, false, false, NULL, false }
};
Index: doc/extend.texi
===================================================================
--- doc/extend.texi (revision 223720)
+++ doc/extend.texi (working copy)
@@ -4858,6 +4858,13 @@ On x86-32 targets, the @code{stdcall} attribute ca
assume that the called function pops off the stack space used to
pass arguments, unless it takes a variable number of arguments.
+@item noplt
+@cindex @code{noplt} function attribute, x86-64
+@cindex functions whose calls do not go via PLT
+On x86-64 targets. the @code{noplt} attribute causes the compiler to
+call this external function indirectly using a GOT entry and avoid the
+PLT.
+
@item target (@var{options})
@cindex @code{target} function attribute
As discussed in @ref{Common Function Attributes}, this attribute
Index: testsuite/gcc.target/i386/noplt-1.c
===================================================================
--- testsuite/gcc.target/i386/noplt-1.c (revision 0)
+++ testsuite/gcc.target/i386/noplt-1.c (working copy)
@@ -0,0 +1,13 @@
+/* { dg-do compile { target x86_64-*-linux* } } */
+
+
+__attribute__ ((noplt))
+void foo();
+
+int main()
+{
+ foo();
+ return 0;
+}
+
+/* { dg-final { scan-assembler "call\[ \t\]\\*.*foo.*@GOTPCREL\\(%rip\\)" } }
*/
Index: testsuite/gcc.target/i386/noplt-2.c
===================================================================
--- testsuite/gcc.target/i386/noplt-2.c (revision 0)
+++ testsuite/gcc.target/i386/noplt-2.c (working copy)
@@ -0,0 +1,13 @@
+/* { dg-do compile { target x86_64-*-linux* } } */
+/* { dg-options "-O2" } */
+
+
+__attribute__ ((noplt))
+int foo();
+
+int main()
+{
+ return foo();
+}
+
+/* { dg-final { scan-assembler "jmp\[ \t\]\\*.*foo.*@GOTPCREL\\(%rip\\)" } }
*/
