How to retrieve IntToPtr from StoreInst?

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1

hi,

i am writing a simple LLVM pass to analyze the Store instruction.
my pass derives from InstVisitor class, and the method to handle Store instruction is like this:

void MyPass::visitStoreInst(StoreInst &I) {
…
}

It is pretty simple to handle Store. however, in on test i got an instruction like below:

store i8 %tmp5, i8* inttoptr (i32 301959828 to i8*)

the second operand is “i8* inttoptr (i32 301959828 to i8*)”, and i have no idea how i can retrieve the address 301959828, given the StoreInst argument of visitStoreInst.

i am looking in the the code of LLVM, but still fail to see how to extract this information.

any suggestion is very appreciated. i am really struggling here now …

thanks so much.
Jun

2

The inttoptr used here is a Constant Expression (llvm::ConstantExpr). You’ll need to take the operand to the store, cast it to llvm::ConstantExpr, and then examine the opcode and operands of the constant expression. The ConstantExpr class is documented at and is described in the LLVM Language Reference Manual. – John T.

3

OK, I tried my best, and come up with code like below:

void MyPass::visitStoreInst(StoreInst &I)
{
    Value *op2 = I.getOperand(1); // the address where we store data

    if (const ConstantExpr *c = dyn_cast <ConstantExpr>(op2)) {
    // how to extract the Int Constant here?
    }
}

The problem is that given ConstantExpr, i am not sure how to extract the
Int Constant operand.
According to http://llvm.org/doxygen/classllvm_1_1ConstantExpr.html, this
class only provides method such as getWithOperands(), but this method
doesnt seem to do what I want.

I grep through the code of LLVM, but cannot find any example doing this.

any more hint, please?

Thanks,
Jun

4

Hi,

According to http://llvm.org/doxygen/classllvm_1_1ConstantExpr.html, this
class only provides method such as getWithOperands(), but this method doesnt
seem to do what I want.

At the top is DECLARE_TRANSPARENT_OPERAND_ACCESSORS, which means you
can call "getOperand(OpNum)" and so on to access the actual operands.
Presumably in your simple case the first operand will be (castable to)
an instance of ConstantInt, which you can call "getZExtValue" on. With
appropriate checks, obviously.

Tim.