[LLVMdev] InstVisitor Example

[Vikram S. Adve]

Brice,

As Luke said, you can find all *uses* of the function name 'strcpy' by  
iterating over all the uses.  If you just need to replace one function  
with another one without changing the arguments being passed, that is  
enough even for indirect calls (within the code being compiled, not  
external code) because you will find all the places where the function  
address is taken.

If you want to modify the arguments being passed, you need to find the  
actual call sites, which requires the call graph (include/Analysis/ 
CallGraph.h).

--Vikram
Associate Professor, Computer Science
University of Illinois at Urbana-Champaign
http://llvm.org/~vadve



On Apr 14, 2009, at 1:13 PM, Luke Dalessandro wrote:

>
> On Apr 14, 2009, at 1:49 PM, Luke Dalessandro wrote:
>
>>
>> On Apr 14, 2009, at 12:48 PM, Brice Lin wrote:
>>
>>> I just read the LLVM Programmer's Manual, which mentions (but
>>> specifically does not include any details of) the InstVisitor
>>> template. Could someone please provide an example of how to use this
>>> template to find (as an example) all CallSites for the function
>>> strcpy?
>>
>> If this is really what you want to do, then the easiest method is to
>> just get the declaration of the strcpy function, and iterate over its
>> uses.
>
> I guess I should note that the "use iteration" will only work for
> direct calls. If you are concerned with indirect calls you need an
> alias analysis or call graph or some such thing. There are lots of
> ways to deal with this.
>
> Also, you might need to be smarter about the Instruction check if you
> expect ConstantExpr casts or any other such use of the declaration.
>
> Luke
>
>>
>>
>>  Function* const strcpy = m.getFunction("strcpy");
>>  for (Value::use_iterator i = strcpy->use_begin(), e = strcpy-
>>> use_end(); i != e; ++i)
>>    if (Instruction* const use = dyn_cast<Instruction>(i)) {
>>      // Do what you need here
>>      CallSite call(use);
>>      ...
>>    }
>>
>> If you want to know how to use InstVisitor for other purposes, you
>> just derive a class from the InstVisitor template, and overload the
>> visit routines that you want.
>>
>>  class StrcpyVisitor : public InstVisitor<StrcpyVisitor> {
>>    void handleStrcpy(CallSite strcpy);
>>    string strcpyName;
>>   public:
>>    void visitCallInst(CallInst& call) {
>>      if (call.getName() == strcpyName)
>>        handleStrcpy(&call);
>>    }
>>    void visitInvokeInst(InvokeInst& invoke) {
>>      if (call.getName() == strcpyName)
>>        handleStrcpy(&invoke);
>>    }
>>  };
>>
>> Then, you probably want to inherit from ModulePass, or FunctionPass,
>> or BasicBlockPass, or whatever makes sense, and in the relevant
>> runOnX(X& x) callback you say:
>>
>>  bool runOnX(X& x) {
>>    visit(x);
>>    return true/false/something_computed;
>>  }
>>
>> Hope this helps,
>> Luke
>>
>>>
>>>
>>> Thanks,
>>> Brice Lin
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