[LLVMdev] Assertion `castIsValid(getOpcode(), S, Ty) && "Illegal BitCast"' failed.

[Nick Lewycky]

bhavani krishnan wrote:
> ok.. So I am trying out what you have suggested. I have written the below code which basically tries to write the constant 10 to a file. myprint is a function pointer to a function which takes char * parameter and writes it to file.
> 
> Value *Ten = ConstantInt::get(Type::Int32Ty, 10);
> const Type *VoidPtrTy = PointerType::getUnqual(Type::Int8Ty);
> AllocaInst *AI = new AllocaInst(Type::Int32Ty);
> Value *ST = new StoreInst(Ten,AI,false,4,j);

Realize that StoreInst's don't have a result. A 'store' does not 
evaluate to a particular value at run time. Its type is Void.

> Value *BT = new BitCastInst(ST,VoidPtrTy,"",j);

Trying to cast (void) to (void*) is invalid. Instead, you should cast 
the AllocaInst, ala:

   Value *BT = new BitCastInst(AI,VoidPtrTy,"",j);

Nick

> CallInst *CallPrint = CallInst::Create(myprint, BT, "", j);
> CallPrint->setTailCall(true);
> 
> I am getting the following error while executing.
>  Assertion `castIsValid(getOpcode(), S, Ty) && "Illegal BitCast"' failed.
> 
> What am I doing wrong :(? I always get stuck badly when these assertions fail :(. Please help me out here. 
> 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
>> Cc: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>, "John Criswell" <criswell at uiuc.edu>
>> Date: Sunday, November 16, 2008, 9:22 PM
>> On Sun, Nov 16, 2008 at 7:54 AM, bhavani krishnan
>> <bhavi63 at yahoo.com> wrote:
>>> 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?
>>
>> Well, you can do something like the following:
>> define i32 @f() nounwind {
>> entry:
>> 	%x = alloca i32
>> 	%resulttoprint = call i32 (...)* @a() nounwind
>> ;start instrumentation
>> 	store i32 %resulttoprint, i32* %x, align 4
>> 	%x1 = bitcast i32* %x to i8*
>> 	call void @print(i8* %x1) nounwind
>> ;end instrumentation
>> 	ret i32 %resulttoprint
>> }
>>
>> That said, you might need to do something that's aware
>> of the type of
>> the result; printing a value in human-readable form
>> requires calling
>> something like printf.
>>
>> -Eli
> 
> 
> 
>       
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