Instrumenting Various Types Using Single Instrumentation Function

Hi All,

My instrumentation code needs to insert calls to transmit Value list. Each element in this list could be of different type. The list is sent to instrumenting function say void recordVarInputValues(int num, …) . So, I have created a Union type in Tracing.cpp, which I link with my benchmark module at compile time. These steps are similar to giri instrumentation

union NumericType
int iValue;
long lValue;
double dValue;


Now, I would like to convert all the llvm Values, required by recordVarInputValues function, to be of NumericType. So that a variable length list of NumerricType values can be passed to my instrumentation function. This way I will not have to create different instrumentation functions for different data types.

Can I cast say i32 value to NumericType value in my instrumentation code, without inserting additional instructions in my benchmark code. I tried inserting bitcast instructions and it doesn’t work for me…

if(!CastInst::isCastable(Lvals[j]->getType(), UnionVar->getType())){
errs()<<“CAST TO NumericType NOT POSSIBLE\n”;
CastInst *I = CastInst::CreateZExtOrBitCast(Lvals[j], UnionVar->getType(), “”, F);

Is this even possible or some other method will be better?


Dear Manish,

Union types in LLVM are points to structures, so casting 8, 16, 32, and 64 bit values to a union pointer is probably not what you want.

I think the easiest thing to do is to:

1) Change the function in your run-time library to take the largest integer size supported by your target.

2) Change the instrumentation code to cast all values (including pointers) to this type.

I'm not sure if CastInst::isCastable() is what you want to use to check to see that the casting can be done. I would just go ahead and use the bit-cast since, for the call, you should always be casting from a type with lower bit-width to higher bit-width. If you enable assertions when you build LLVM, then you should get an assertion if you try to create a Bitcast instruction that isn't going to work.


John Criswell

Thanks again John. I am working on it. Once I get it working. I will post the relevant instructions for others to take a look, in future, and complete the loop. Thanks again.