[LLVMdev] How can i differentiate pointer type int 32* from int 32** ?

John Criswell
Sat, 18 Jul 2015 14:54:11 -0000

On 7/17/15 8:32 PM, Shen Liu wrote:
> John, thanks for your helpful advice.
>
> My ultimate goal is to construct a full instruction-level program
> dependence graph for a given IR file. The hard point is how to
> establish the correct data dependence edges when some function
> arguments are multi-level pointers. To solve this problem I hope to
> check the point-to level for each pointer variable. I think the data
> dependence through pointers can be described more accurately in this
> way. Unfortunately i didn't find any available interface to finish
> this job, so i guess i have to write it by myself.

It sounds like you need a shape graph.  DSA can provide that, and it
currently works with LLVM mainline.  You can find it in the poolalloc
module (svn co http://llvm.org/svn/llvm-project/poolalloc/trunk
poolalloc) or a slightly older version on my Github page
(https://github.com/jtcriswell/llvm-dsa).  Please note that the version
from LLVM SVN will only compile lib/DSA.  I don't think anyone has
brought lib/PoolAllocate up to date.

There is documentation which gives a very basic overview of the DSA
passes and how to use the shape graph.

The open question is whether DSA will be sufficiently accurate for your
needs.  Of that, I'm not sure.  You would need to try it out and see if
it's sufficient accurate for you.

Regards,

John Criswell


>
> Best regards,
>
> Shen
>
>
>
> On Fri, Jul 17, 2015 at 2:22 PM, John Criswell <jtcriswel at gmail.com
> <mailto:jtcriswel at gmail.com>> wrote:
>
>     On 7/17/15 1:06 PM, Shen Liu wrote:
>>      John, thanks for you answer! But as far as I know LLVM doesn't
>>     provide any interface for finding the pointee of a pointer
>>     directly, so i have to process a multi-level pointer i need to
>>     write my own function to check pointers level by level, is that
>>     right?
>
>     I'm not sure what you're trying to do.  If you're trying to
>     determine the LLVM pointer type and the LLVM type to which it
>     points, what I've said will work.
>
>     If you're trying to do something more complicated, then you need
>     to explain more clearly what you want to do.  I think it would
>     also help if you "jumped up a level" and explained what your
end
>     goal is so that the community can give you better advice.  Based
>     on your previous emails, it seems like you're asking very specific
>     questions instead of asking how to best achieve your overall goal.
>
>     Regards,
>
>     John Criswell
>
>
>>
>>     On Fri, Jul 17, 2015 at 1:47 PM, John Criswell
>>     <jtcriswel at gmail.com <mailto:jtcriswel at
gmail.com>> wrote:
>>
>>         On 7/17/15 12:38 PM, Shen Liu wrote:
>>>         Hi all, as a LLVM beginner I would like to know how can i
>>>         check the pointer types with different levels like int 32*
>>>         and int 32**, int 32***?
>>>
>>>         By using value->getType()->isPointerTy() i can just
know
>>>         they are pointers. But the dump results clearly show they
>>>         are different. Is there a good way to calculate their
actual
>>>         point to levels? Thanks!
>>
>>         You will need to use dyn_cast<PointerType> to cast the
Type *
>>         into a PointerType *.  Once you do that, you can find the
>>         Type * that the PointerType points to.
>>
>>         Regards,
>>
>>         John Criswell
>>
>>>
>>>
>>>         Best regards,
>>>
>>>         Shen
>>>
>>>
>>>         _______________________________________________
>>>         LLVM Developers mailing list
>>>         LLVMdev at cs.uiuc.edu  <mailto:LLVMdev at
cs.uiuc.edu>          http://llvm.cs.uiuc.edu
>>>         http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>>         --
>>         John Criswell
>>         Assistant Professor
>>         Department of Computer Science, University of Rochester
>>         http://www.cs.rochester.edu/u/criswell
>>
>>
>
>
>     --
>     John Criswell
>     Assistant Professor
>     Department of Computer Science, University of Rochester
>     http://www.cs.rochester.edu/u/criswell
>
>


--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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