llvm dev - Sep 2014 - [LLVMdev] 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
https://github.com/liuml07/giri

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";
      exit(0);
    }
    CastInst *I = CastInst::CreateZExtOrBitCast(Lvals[j],
UnionVar->getType(), "", F);


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

Thanks!
Manish
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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.

Regards,

John Criswell


On 9/1/14, 4:50 PM, Manish Gupta wrote:
> 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 https://github.com/liuml07/giri
>
> 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";
>       exit(0);
>     }
>     CastInst *I = CastInst::CreateZExtOrBitCast(Lvals[j], 
> UnionVar->getType(), "", F);
>
> Is this even possible or some other method will be better?
>
> Thanks!
> Manish
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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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.


On Mon, Sep 1, 2014 at 5:13 PM, John Criswell <jtcriswel at gmail.com>
wrote:
>  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.
>
> Regards,
>
> John Criswell
>
>
>
> On 9/1/14, 4:50 PM, Manish Gupta wrote:
>
>  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
> https://github.com/liuml07/giri
>
>  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";
>       exit(0);
>     }
>     CastInst *I = CastInst::CreateZExtOrBitCast(Lvals[j],
> UnionVar->getType(), "", F);
>
>
>  Is this even possible or some other method will be better?
>
>  Thanks!
> Manish
>
>
> _______________________________________________
> LLVM Developers mailing listLLVMdev at cs.uiuc.edu        
http://llvm.cs.uiuc.eduhttp://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
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