[LLVMdev] How to lower the intrinsic function 'llvm.objectsize'?

[Dingbao Xie]

Thanks for your reply.
I'm attempting to expand KLEE to support this intrinsic function.
That's why I need to handle this myself.
According to the reply, the correct implementation should first find the
definition of the object and then determine the
size of the object.
BTW, can I just refer to the implementation in InstCombineCalls.cpp.


On Wed, Nov 5, 2014 at 2:24 PM, Matt Arsenault <Matthew.Arsenault at amd.com>
wrote:

>  On 11/05/2014 02:04 PM, Dingbao Xie wrote:
>
>  The documentation of LLVM says that "The llvm.objectsize intrinsic is
> lowered to a constant representing the size of the object concerned". I'm
> attempting to lower this intrinsic function to a constant in a pass. Below
> is the code snippet that I wrote:
>
> Why do you need to handle this yourself? This should already be handled
> for you (see InstCombineCalls.cpp). However, you have a few problems with
> this.
>
>   for (BasicBlock::iterator i = b.begin(), ie = b.end();
>    (i != ie) && (block_split == false);) {
>  IntrinsicInst *ii = dyn_cast<IntrinsicInst>(&*i);
>  ++i;
>  if(ii) {
>  switch (ii->getIntrinsicID()) {
>   case Intrinsic::objectsize: {
>    IRBuilder<> builder(ii->getParent(), ii);
>    Value *op1 = ii->getArgOperand(0); //i8*
>    uint64_t bit_size = op1->getType()->getPointerElementType()->getPrimitiveSizeInBits();
>
>   First, you can't always determine the size. Just looking at the pointer
> element type isn't enough. This requires finding the object definition,
> which can fail, and the existing handling uses llvm::getObjectSize to for.
> In general when looking at type sizes you don't want to use
> getPrimitiveSizeInBits, and should use the DataLayout for various reasons.
>
>
>    Value *result = ConstantInt::get(ii->getType(), bit_size);
>    ii->replaceAllUsesWith(result);
>    ii->removeFromParent();
>    delete ii;
>
>   You shouldn't use delete here. You probably want ii->eraseFromParent().
>
>
>    break;
>   }
>  }
> }
>
> I'm new to LLVM and not sure whether the implementation is correct. Can
> anybody tell me whether the implementation is correct?
>
> Thanks in advance.
>
>
> --
>  Dingbao Xie
>
>
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>
>
>


-- 
Dingbao Xie
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