[LLVMdev] How do I get the result of an instruction?

[bhavani krishnan]

Hi,

I am writing an optimization pass where I need to instrument the code such that I need to store the results of some instructions in file. Using llc -march=cpp option I figured out how to add a function(say writeToFile) which takes char* parameter and writes to file. Now, I need put in a CallInst which calls writeToFile passing the Instruction result as parameter. How do I do this? 

So, in my optimization pass...
Func *myprint = makewriteToFile() //creates a function which writes to file
for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
{
        blk=i;
        for (BasicBlock::iterator j = blk->begin(), k = blk->end(); j != k; ++j){
            Instruction *inst = j;
            //if inst satisfies my condition, write reults to file
            CallInst *CallPrint = CallInst::Create(myprint, ???, "", j);
            CallPrint->setTailCall(true);
       }
}       
What do I put in the ???. How do I cast Instruction *inst into char * which can be passed into the function?


Hope this is clear.
Thanks,
Bhavani


--- On Sun, 11/16/08, Eli Friedman <eli.friedman at gmail.com> wrote:

> From: Eli Friedman <eli.friedman at gmail.com>
> Subject: Re: [LLVMdev] How do I get the result of an instruction?
> To: bhavi63 at yahoo.com, "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
> Cc: "John Criswell" <criswell at uiuc.edu>
> Date: Sunday, November 16, 2008, 6:35 AM
> On Sat, Nov 15, 2008 at 3:58 PM, bhavani krishnan
> <bhavi63 at yahoo.com> wrote:
> > Thanks!
> >
> > How do I cast the result to a string? I basically need
> to store the results of some instructions in a file.
> 
> If you're confused about how the IR works,
> http://llvm.org/demo/ can
> be useful.  The question you're asking doesn't
> really seem to make
> sense.
> 
> -Eli