[LLVMdev] How to describe a pointer that points to All memory(include global memory, heap, stack)?

[Steven Su]

Hi, John
        I am building a flow sensitive intra-procedural alias analysis(without interprocedural info).
	So, the first thing I have to consider is where a parameter-pointer or a global-pointer might point to.
	Then I defined several special Virtual Memory Locations: ALL_MEMORY, GLOBAL_MEMORY, STACK_MEMORY, HEAP_MEMORY. ALL_MEMORY contains GLOBAL_MEMORY, STACK_MEMORY, HEAP_MEMORY.
	
	e.g1: 
	extern int * q;
	void f(int * p)
	{
	    int a;
	    *p = 0; //STMT1
	    *q = a; //STMT2
	}
	For above case, both p and q pointed to ALL_MEMORY: p->ALL_MEMORY, q->ALL_MEMORY.
	And each STMT has two BitVectors to describe MayDef, MayUse.
	(I think the BitVector must be sparse, otherwise the alias-analysis module need too much memory to allocate for all BitVectors.)
	For STMT1, the MayDef={ALL_MEMORY}, MayUse={}
	For STMT2, the MayDef={ALL_MEMORY}, MayUse={'a'}
	---------------------
	e.g2: 
	extern int A[100];
	int * q;
	void f2(int * p)
	{
	    *p = 0; //STMT1
	    p = &A; //STMT2
	    p[0] = *q; //STMT3
	    bar(); //STMT4
	}
	In e.g2, 
	for STMT1, the MayDef={ALL_MEMORY}, MayUse={}
	for STMT2, p->A, so the MayDef={'p'}, MayUse={}
	for STMT3, the MayDef={'A'}, MayUse={ALL_MEMORY}
        for STMT4, the MayDef={ALL_MEMORY}, MayUse={ALL_MEMORY}

Is that right? Or there are another better methods. :)
	


--- 13年3月14日，周四, John Criswell <criswell at illinois.edu> 写道：

> 发件人: John Criswell <criswell at illinois.edu>
> 主题: Re: [LLVMdev] How to describe a pointer that points to All memory(include global memory, heap, stack)?
> 收件人: "Steven Su" <steven_known at yahoo.com.cn>
> 抄送: llvmdev at cs.uiuc.edu
> 日期: 2013年3月14日,周四,上午12:14
> On 3/13/13 4:06 AM, Steven Su wrote:
> > Hello, could any one point me following question.
> 
> Without any context, your question is difficult to
> answer.  Are you 
> building a points-to analysis and wanting to know how an
> alias analysis 
> might encode the fact that a pointer could alias any other
> pointer?
> 
> -- John T.
> 
> >
> > e.g:
> >     void foo(int * p)
> >     {
> >            *p =
> 0;            
> >     }
> >          Here 'p' may point to
> all memory location.
> >          Could you tell me how
> to represent the POINT TO set of 'p'?
> >        
>     
> >          Here is my solution:
> >          Introduce a
> memory-class named: Global_Mem, then p pointed to
> global_mem.
> >          And the MOD set of
> '*p=0' is Global_Mem.
> >
> > But how to present the overlapping alias set:
> > e.g2:
> >          extern A[100];
> >     void foo(int * p, int i)
> >     {
> >             *p
> = 0;
> >         
>    A[i] = 10;
> >     }
> >
> > 'p' may point to anywhere. So p may point to A. How to
> describe the relation?
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu 
>        http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
>