PATCH: [4.1 Regression]: java compiler generates wrong code on ia64

[Bryce McKinlay]

H. J. Lu wrote:

>On Mon, Apr 18, 2005 at 12:34:04PM -0700, H. J. Lu wrote:
>  
>
>>On Mon, Apr 18, 2005 at 12:16:10PM -0700, H. J. Lu wrote:
>>    
>>
>>>On Mon, Apr 18, 2005 at 03:03:02PM -0400, Bryce McKinlay wrote:
>>>      
>>>
>>>>H. J. Lu wrote:
>>>>
>>>>        
>>>>
>>>>>>The function pointers in the GCJ method metadata (_Jv_Method) are always 
>>>>>>local, except in the case of CNI functions. But, even local function 
>>>>>>references in a .so will point at PLT entries if the function is also 
>>>>>>referenced from the main binary.
>>>>>>  
>>>>>>
>>>>>>            
>>>>>>
>>>>>Whan you said "local function", did you mean
>>>>>
>>>>>1. A local data variable with function type. Or
>>>>>2. A function symbol which isn't visible to the outside. Or
>>>>>3. A global data variable with function type pointing to a local
>>>>>function.
>>>>>
>>>>>I ran into a very tricky issue. But I don't have a testcase. This
>>>>>problem may be related.
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>I mean "a reference to a function which is public (visible to the 
>>>>outside) and defined within the same compilation unit"
>>>>        
>>>>
>>>That makes senses now. For me, "local function" means a different
>>>thing :-). If you want to know if a function will be bound locally
>>>at the run time, you should use targetm.binds_local_p. I think this
>>>patch is correct.
>>>
>>>
>>>H.J.
>>>---
>>>2005-04-18  H.J. Lu  <hongjiu.lu@intel.com>
>>>
>>>	PR java/21070
>>>	* class.c (make_local_function_alias): Use targetm.binds_local_p
>>>	to check if a function is bound locally.
>>>
>>>      
>>>
>>Second thought. Since you can only create an aliase for a symbol
>>defined within the same file, targetm.binds_local_p alone may not be
>>suitable for this purpose.
>>
>>    
>>
>
>I am not familiar with Java semantics. targetm.binds_local_p will
>tell you if a function may be discarded at the link time or overriden
>by something else at the run time. If a function is public and defined
>within the same compilation unit, it can be discarded at the link time
>due to linkonce/comdat and can be overriden by dynamic linker. If it is
>discarded or overriden, does a local alias make any more senses for
>Java? It seems that
>
>  if (DECL_EXTERNAL (method) || !targetm.binds_local_p (method))
>    return method;
>
>will make sure that an aliase will only be created when the function
>is defined within the compilation unit and won't be discarded or
>overriden.
>  
>

Well, this is certainly the behaviour we would like for Java, but AFAIK 
we have no way to ensure that something always binds locally.

binds_local_p is described as:

  /* True if EXP names an object for which name resolution must resolve
     to the current module.  */

It seems to me that, given ELF semantics, a public symbol can always be 
overriden by the linker at runtime, thus targetm.binds_local_p will 
always be false? If there was some way to force targetm.binds_local_p 
then we wouldn't need make_local_function_alias()!

Bryce