llvm dev - Nov 2010 - [LLVMdev] the called function equal NULL

Hi,

I have a llvm-pass in hand written by other people. There are following
statements that I couldn't understand:

-------------------------------program----------------------------------------------------
...
if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) {
    const CallSite cs(inst);
    if (cs.getCalledFunction() == NULL)
      return dealAtIndirectCall(cs);
    else
      return dealAtDirectCall(cs);
}
...
-------------------------------------------------------------------------------------------

My question is:

When does the called function equal NULL, could you give an example?  I mean
what kind of call in source code could change to this case in llvm-IR, could you
give an example?

Thank you for your time.

Best Regards

2010-11-30 



WeiHu
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On Nov 29, 2010, at 5:22 PM, huwei8717 wrote:
> Hi,
>  
> I have a llvm-pass in hand written by other people. There are following
statements that I couldn't understand:
>  
>
-------------------------------program----------------------------------------------------
> ...
> if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) {
>     const CallSite cs(inst);
>     if (cs.getCalledFunction() == NULL)
>       return dealAtIndirectCall(cs);
>     else
>       return dealAtDirectCall(cs);
> }
> ...
>
-------------------------------------------------------------------------------------------
>  
> My question is:
>  
> When does the called function equal NULL, could you give an example?  I
mean what kind of call in source code could change to this case in llvm-IR,
could you give an example?
A call to a value of function-pointer type, e.g.
  void callit(void (*f)()) { f(); }

Virtual calls in C++ would also have no known called function.

John.
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Than you John, It's very nice of you.

Best Regards

2010-11-30 



-Wei



发件人： John McCall 
发送时间： 2010-11-30  09:26:17 
收件人： huwei8717 
抄送： llvmdev 
主题： Re: [LLVMdev] the called function equal NULL 
 


On Nov 29, 2010, at 5:22 PM, huwei8717 wrote:


Hi,

I have a llvm-pass in hand written by other people. There are following
statements that I couldn't understand:

-------------------------------program----------------------------------------------------
...
if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) {
    const CallSite cs(inst);
    if (cs.getCalledFunction() == NULL)
      return dealAtIndirectCall(cs);
    else
      return dealAtDirectCall(cs);
}
...
-------------------------------------------------------------------------------------------

My question is:

When does the called function equal NULL, could you give an example?  I mean
what kind of call in source code could change to this case in llvm-IR, could you
give an example?


A call to a value of function-pointer type, e.g.
  void callit(void (*f)()) { f(); }


Virtual calls in C++ would also have no known called function.


John.
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