[LLVMdev] Question About inserting Instruction?

[Vladimir Prus]

On Wednesday 11 May 2005 14:21, Qiuyu Zhang wrote:

> I am working on a project with LLVM. What I need to do is to
> generate/insert some dummy/dead basic blocls which never have chance to be
> executed and put some instructions in those dummy/dead basic blocks.
>
> So far, the dummy/dead BB insertion is done. I am trying insert
> instructions in those dummy/dead BB. Actually, I can insert the legal
> instructions to dummy/dead BB, however, I really want to insert some
> illegal instructions/any thing into those BB since those instructions have
> no chance to be executed. I am not sure if it could be done or not.
>
> For example,
>  Correct way:
>     Instruction *NewInst = new LoadInst(...);
>     NewBB->getInstList().push_back(NewInst);
>
>  what I need just put some junk data in the BB, not instructions. From
> assemble code level, it looks like the following,
.....
>     what I tried is to make *NewInst point to random memory(cast to
> Instuction pointer) and push_back to instList. But I failed to do it.
>
>             Instruction *NewInst  =  ;
>             NewBB->getInstList().push_back(NewInst);
>
> So I was wondering if it is allowed in LLVM or not, if so, how to do that?
>
> Let me know if my question is not clear.

Actually, it's not clear. Why do you want to put bogus Instruction* pointers 
into basic blocks? If you are not going to ever use those instructions, you 
can create/insert instances of UnreachableInst, or any other instruction you 
like.

If you do want to use the inserted instructions in any way, then inserting 
bogus Instruction* pointers would just crash your application.

- Volodya




>
> Thanks
> Qiuyu