This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: RFA: Remove alias usage from libgcc/sync.c


Richard Biener <richard.guenther@gmail.com> writes:
>>> Honza?  For tailr this boils down to symtab_semantically_equivalent_p ().
>>> I suppose we don't want to change that but eventually special case
>>> builtins in tailr, thus
>>>
>>> Index: gcc/tree-tailcall.c
>>> ===================================================================
>>> --- gcc/tree-tailcall.c (revision 203409)
>>> +++ gcc/tree-tailcall.c (working copy)
>>> @@ -446,7 +446,9 @@ find_tail_calls (basic_block bb, struct
>>>    /* We found the call, check whether it is suitable.  */
>>>    tail_recursion = false;
>>>    func = gimple_call_fndecl (call);
>>> -  if (func && recursive_call_p (current_function_decl, func))
>>> +  if (func
>>> +      && ! DECL_BUILT_IN (func)
>>> +      && recursive_call_p (current_function_decl, func))
>>>      {
>>>        tree arg;
>>>
>>> which makes -O2 not turn it into an infinite loop (possibly also applies
>>> to the original code with the alias declaration?)
>>
>> If that's OK then I'm certainly happy with it :-)
>
> I'm happy with the tailcall change (if you can do the testing ... ;))

Thanks.

>>  FWIW, the alias case
>> was first optimised from __sync_synchronize->sync_synchronize, before it
>> got converted into a tail call.  That happened very early in the pipeline
>> and I suppose would stop the built-in expansion from kicking in,
>> even with tail calls disabled.  But if we say that:
>>
>> foo () { foo (); }
>>
>> is a supported way of defining out-of-line versions of built-in foo,
>> then that's much more convenient than the aliases anyway.
>
> Btw, if it is supported then we should add a testcase that makes sure
> we don't regress for this.  (I wouldn't say we should document this
> "feature" just in case we want to decide it's not the way we want it
> in the future).

OK, I adjusted the x86 test I posted on gcc@ (and fixed the \; problem
Jakub pointed out).

Tested on x86_64-linux-gnu and mips64-linux-gnu.  OK to install?

Thanks,
Richard


gcc/
2013-10-15  Richard Biener  <rguenther@suse.de>

	* tree-tailcall.c (find_tail_calls): Don't use tail-call recursion
	for built-in functions.

gcc/testsuite/
	* gcc.dg/torture/builtin-self.c: New file.

libgcc/
	* sync.c: Remove static aliases and define each function directly
	under its real name.

Index: gcc/tree-tailcall.c
===================================================================
--- gcc/tree-tailcall.c	2013-10-15 08:52:07.358853220 +0100
+++ gcc/tree-tailcall.c	2013-10-15 08:53:06.980419473 +0100
@@ -446,7 +446,9 @@ find_tail_calls (basic_block bb, struct
   /* We found the call, check whether it is suitable.  */
   tail_recursion = false;
   func = gimple_call_fndecl (call);
-  if (func && recursive_call_p (current_function_decl, func))
+  if (func
+      && !DECL_BUILT_IN (func)
+      && recursive_call_p (current_function_decl, func))
     {
       tree arg;
 
Index: gcc/testsuite/gcc.dg/torture/builtin-self.c
===================================================================
--- /dev/null	2013-10-13 08:29:45.608935301 +0100
+++ gcc/testsuite/gcc.dg/torture/builtin-self.c	2013-10-15 08:58:00.064045777 +0100
@@ -0,0 +1,10 @@
+/* { dg-do compile { target i?86-*-* x86_64-*-* } } */
+/* Check that we can use this idiom to define out-of-line copies of built-in
+   functions.  This is used by libgcc/sync.c, for example.  */
+void __sync_synchronize (void)
+{
+  __sync_synchronize ();
+}
+/* { dg-final { scan-assembler "__sync_synchronize" } } */
+/* { dg-final { scan-assembler "\t(lock|mfence)" } } */
+/* { dg-final { scan-assembler-not "\tcall" } } */
Index: libgcc/sync.c
===================================================================
--- libgcc/sync.c	2013-10-15 08:52:07.358853220 +0100
+++ libgcc/sync.c	2013-10-15 08:53:06.981419482 +0100
@@ -72,22 +72,22 @@ Software Foundation; either version 3, o
    TYPE is a type that has UNITS bytes.  */
 
 #define DEFINE_V_PV(NAME, UNITS, TYPE)					\
-  static TYPE								\
-  NAME##_##UNITS (TYPE *ptr, TYPE value)				\
+  TYPE									\
+  __##NAME##_##UNITS (TYPE *ptr, TYPE value)				\
   {									\
     return __##NAME (ptr, value);					\
   }
 
-#define DEFINE_V_PVV(NAME, UNITS, TYPE)				\
-  static TYPE								\
-  NAME##_##UNITS (TYPE *ptr, TYPE value1, TYPE value2)			\
+#define DEFINE_V_PVV(NAME, UNITS, TYPE)					\
+  TYPE									\
+  __##NAME##_##UNITS (TYPE *ptr, TYPE value1, TYPE value2)		\
   {									\
     return __##NAME (ptr, value1, value2);				\
   }
 
 #define DEFINE_BOOL_PVV(NAME, UNITS, TYPE)				\
-  static _Bool								\
-  NAME##_##UNITS (TYPE *ptr, TYPE value1, TYPE value2)			\
+  _Bool									\
+  __##NAME##_##UNITS (TYPE *ptr, TYPE value1, TYPE value2)		\
   {									\
     return __##NAME (ptr, value1, value2);				\
   }
@@ -118,9 +118,7 @@ #define local_sync_lock_test_and_set DEF
 #define DEFINE1(NAME, UNITS, TYPE) \
   static int unused[sizeof (TYPE) == UNITS ? 1 : -1]	\
     __attribute__((unused));				\
-  local_##NAME (NAME, UNITS, TYPE);			\
-  typeof (NAME##_##UNITS) __##NAME##_##UNITS		\
-    __attribute__((alias (#NAME "_" #UNITS)));
+  local_##NAME (NAME, UNITS, TYPE);
 
 /* As above, but performing macro expansion on the arguments.  */
 #define DEFINE(NAME, UNITS, TYPE) DEFINE1 (NAME, UNITS, TYPE)
@@ -167,13 +165,11 @@ DEFINE (FN, 8, UOItype)
 
 #if defined Lsync_synchronize
 
-static void
-sync_synchronize (void)
+void
+__sync_synchronize (void)
 {
   __sync_synchronize ();
 }
-typeof (sync_synchronize) __sync_synchronize \
-  __attribute__((alias ("sync_synchronize")));
 
 #endif
 


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]