[LLVMdev] InstVisitor Example

[Luke Dalessandro]

Brice Lin wrote:
> Thanks for providing me with those examples. My rather inefficient
> pass, which inherits from ModulePass, currently iterates through the
> Module, Functions, and BasicBlocks multiple times (once to find
> strcpy, another to find strcat, and so on for various other
> functions). If I only care about the direct calls, would I benefit
> more from switching to multiple use_iterators or the InstVisitor
> template?

I think use_iterators are probably the best for you if that's all you 
want. It is the most efficient because you only touch the actual users 
of each function, and it leads to really clear code. On the other hand, 
it works best in a ModulePass setting. If you want something for a 
smaller granularity the InstVisitor is probably as good a choice, as 
your runOnX function just ends up calling visit(x).

Luke

> 
> - Brice
> 
> On Tue, Apr 14, 2009 at 1:13 PM, Luke Dalessandro
> <luked at cs.rochester.edu> wrote:
>> On Apr 14, 2009, at 1:49 PM, Luke Dalessandro wrote:
>>
>> 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
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev