[LLVMdev] dyn_cast<Instruction *> returns NULL where it should return a valid instruction

[Chuck Zhao]

I have the following prototype for a function:
void bkp_memory(char *, int);

Inside my LLVM IR, I have a callsite looks like the following:

tail call void @bkp_memory(i8* bitcast (i32** @P to i8*), i32 4) nounwind



When I try to obtain its 1st argument and check whether it is a valid 
instruction, using:
Instruction *Inst = dyn_cast<Instruction *>(I->getOperand(0));

it gives me a NULL Ptr, which is quite a surprise to me.

Am I doing anything wrong here?


Note that in many other cases, the bkp_memory() callsite won't have the 
embedded form. They look like:

   store i32* %21, i32** @P, align 4
   %22 = bitcast i32* %21 to i8*
   tail call void @bkp_memory(i8* %22, i32 4) nounwind

And the dyn_cast<>  conversion is fine in these cases.

Would that be the problem?


Thank you

Chuck

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