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

[Dan Liew]

Hi Dingbao,

On 5 November 2014 22:37, Dingbao Xie <xiedingbao at gmail.com> wrote:
> 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.

Please see this [1] issue on KLEE's issue tracker.

After talking to Daniel (CC'ed) I was under the impression that the
easiest thing to do would be to treat these as no-ops rather than
trying to lower them.

Reading the docs on llvm.objectsize couldn't we just be really lazy
and return 0 or -1 (indicating unknown) depending on the value of the
"min" argument? If there are programs where control flow depends on
the return value of llvm.objectsize() this would probably break things
but I don't know if clang ever generates IR in that form.

What Nuno just suggested sounds quite promising way to do this that
isn't as lazy as what I suggested.

[1] https://github.com/klee/klee/issues/33
[2] http://llvm.org/docs/LangRef.html#llvm-objectsize-intrinsic

Thanks,
Dan.