On Oct 11, 2012, Jason Merrill <ja...@redhat.com> wrote:
> On 10/11/2012 11:14 AM, Alexandre Oliva wrote:
>> How about marking the singleton containing the call to the initializer
>> as always_inline, but not the initializer itself?
>>
>> The compiler can then infer that initialized is set on the first inlined
>> call and optimize away subsequent tests and initializer calls
>> (call_some_function_that_may_modify_memory).
> That would require exporting the initialized flag in addition to the
> initializer function; currently it is private to the translation unit
> with the initializer function. That is, the wrapper currently looks
> like
> int& i_wrap() { if (i_init) i_init(); return i; }
This is not entirely clear to me; where is i defined in the first place?
Is it i_init that defines and tests i_initialized?
I.e., do we translate:
[EXTERN] thread_local T i;
int f()
{
T& j = i;
...
}
to:
[EXTERN] __thread T i;
#if !EXTERN
void
i_init()
{
static __thread bool initialized;
if (!initialized)
{
initialized = true;
i.T();
}
}
#endif
static T&
i_wrap ()
{
if (i_init)
i_init ();
return i;
}
int
f()
{
T& j = i_wrap();
...
}
?
Consider instead the following expansion:
[EXTERN] __thread T i;
#if !EXTERN
static void i_init (void);
__thread void (*i_initialize)(void) = i_init;
static void
i_init ()
{
i_initialize = NULL;
i.T();
}
#else
EXTERN __thread void (*i_initialize)(void);
#endif
static T& __attribute__((__always_inline__))
i_wrap ()
{
if (i_initialize)
{
i_initialize ();
// this is redundant, but it should enable removal of subsequent calls
i_initialize = NULL;
}
return i;
}
or this:
[EXTERN] __thread T *i;
#if !EXTERN
static __thread T i_data;
void
i_init ()
{
i = &i_data; // or maybe allocate it dynamically?
i->T();
}
#else
extern void i_init ();
#endif
static T& __attribute__((__always_inline__))
i_wrap ()
{
if (!i)
i_init ();
return *i; // dereference should enable cse
}
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer
