There are some other cases that I cannot get right answer.
case1: interproceduure
func(int*arg)
{
return arg[0] + arg[1]
}
func2()
{
int a[10]
return func(a);
}
here func cannot tell arg is local var.
case 2: global array point to local
int *array[3]
int func(int x)
{
int sub1[10];
int sub2[10];
int sub3[10];
array[0] = sub1;
array[1]=sub2;
array[2]=sub3;
then refer to array by array[x][y]
}
here i refer to local var, but the points-to cannnot give right answer.
I do not know if this is the points-to analysis problem, or improper use it.
---Original---
From: "Richard Biener"<[email protected]>
Date: Wed, May 13, 2020 19:10 PM
To: "易会战"<[email protected]>;
Cc: "gcc"<[email protected]>;
Subject: Re: how to find variable related to a virtual ssa name
On Wed, May 13, 2020 at 11:38 AM 易会战 <[email protected]> wrote:
>
> now I am working on gcc-9.3, can you give the specific code location to
check not escaped heap? I try to add a flag.
set_uids_in_ptset
> ---Original---
> From: "Richard Biener"<[email protected]>
> Date: Wed, May 13, 2020 17:28 PM
> To: "易会战"<[email protected]>;
> Cc: "gcc"<[email protected]>;
> Subject: Re: how to find variable related to a virtual ssa name
>
> On Wed, May 13, 2020 at 11:08 AM 易会战 <[email protected]> wrote:
> >
> > yes, it does not escape the function, but indeed allocate memory on
heap. There is much specific method to judge the memory on heap although not
escape the function?
>
> Not at the moment. The info is computed by tree-ssa-structalias.c in
> compute_may_aliases,
> the pass knows that a variable points to not escaped heap storage but this
is
> not stored anywhere ready for consumption. Adding a flag to
> pt_solution would be easy though.
>
> Richard.
>
> > ---Original---
> > From: "Richard Biener"<[email protected]>
> > Date: Wed, May 13, 2020 15:00 PM
> > To: "易会战"<[email protected]>;
> > Cc: "gcc"<[email protected]>;
> > Subject: Re: how to find variable related to a virtual ssa name
> >
> > On Wed, May 13, 2020 at 6:03 AM 易会战 <[email protected]> wrote:
> > >
> > > It seems the function ptr_deref_may_alias_global_p cannot give
right result.
> > > For example,
> > > int func(int size, int i)
> > > {
> > > int * sum;
> > > sum = malloc()
> > > ....here some code access sum pointing to memory
> > > return sum[i]
> > > }
> > > ptr_deref_may_alias_global_p tell me it is a local memory
access. indeed sum is a local variable, but the pointer point to heap memory.
> > > In fact there is a similiar function ref_may_alias_global_p, and
it give similiar result.
> >
> > GCC can be clever and notice your malloc() result does not escape the
function
> > which means stores to it are dead once you leave it. For this
reason
> > it does not
> > mark the memory global. So make sure the allocated pointer
escapes
> > and try again.
> >
> > >
> > >
> > > ---Original---
> > > From: "Richard Biener"<[email protected]>
> > > Date: Tue, May 12, 2020 22:20 PM
> > > To: "易会战"<[email protected]>;
> > > Cc: "gcc"<[email protected]>;
> > > Subject: Re: how to find variable related to a virtual ssa name
> > >
> > > On Tue, May 12, 2020 at 4:16 PM 易会战 <[email protected]>
wrote:
> > > >
> > > > thanks a lot. I will check your advice.
> > > > Can you give some explaination about memory ssa, and how to
use it. I check internal, cannot get it. Maybe you know some examples or some
more materials.
> > >
> > > memory SSA in GCC is simply a SSA chain of all memory statements
local
> > > to a function
> > > with a _single_ underlying variable (.MEM) and thus only one SSA
name
> > > live at the same
> > > time. It can be used to quickly traverse stores via
use->def chains
> > > and loads inbetween
> > > two stores via immediate uses.
> > >
> > > Richard.
> > >
> > > > ---Original---
> > > > From: "Richard Biener"<[email protected]>
> > > > Date: Tue, May 12, 2020 22:02 PM
> > > > To: "易会战"<[email protected]>;
> > > > Cc: "gcc"<[email protected]>;
> > > > Subject: Re: how to find variable related to a virtual ssa
name
> > > >
> > > > On Tue, May 12, 2020 at 2:44 PM 易会战 via Gcc
<[email protected]> wrote:
> > > > >
> > > > > hi, I am working on gcc ssa name. For each function,
we can traverse all defined ssa name by macro FOR_EACH_SSA_NAME. If a ssa name
is default definition for a symbol (check SSA_NAME_IS_DEFAULT_DEF) , I can get
the symbol by SSA_NAME_VAR. But for a virtual DEFAULT DEF, I cannot get it,
SSA_NAME_VAR return a identifier named .MEM. I cannot find which variable
related to the default definition. Why and how I should find the related
variable?
> > > > >
> > > > >
> > > > > By the way , I give my current work,&nbsp; I wish
find a MEM_REF refer to global/heap memory or local stack. I try my best to get
a correct memory type. Since MEM_REF have a base address, which is often a ssa
name. Athough it is not virtual ssa name. But I find just check ssa name data
flow is not enough to get the info.
> > > > > For example, a malloc function allocate some heap
memory and record the address in a global ptr. On gimple ssa IR, the malloc
function return a address assigned to a ssa name , then ssa name assign the
value to the global ptr. When i check ssa name defined by the global ptr, I
donot know if the ptr point to global memory or local memory.
> > > > > Please see the gimple code:
> > > > > _2 = malloc()
> > > > > ptr = _2
> > > > > _3 = ptr
> > > > > MEM_REF[BASE _3]
> > > > > I wish get _3&nbsp; is a address pointing to
global memory. But just from _3=ptr, cannot judge it.&nbsp;
> > > > > I wish memory SSA can help solve the problem.
> > > >
> > > > memory SSA will not solve this problem. You can
instead query
> > > > points-to information
> > > > on _3 for example by calling ptr_deref_may_alias_global_p
(_3) which internally
> > > > looks at SSA_NAME_PTR_INFO which contains the solution of
the
> > > > points-to computation.
> > > >
> > > > Richard.
> > > >
> > > > >
> > > > > Or gcc gives the info at other pass? wish get some
advice. Thanks a lot.
