On Wed, May 13, 2020 at 11:38 AM 易会战 <huizha...@foxmail.com> 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"<richard.guent...@gmail.com>
> Date: Wed, May 13, 2020 17:28 PM
> To: "易会战"<huizha...@foxmail.com>;
> Cc: "gcc"<gcc@gcc.gnu.org>;
> Subject: Re: how to find variable related to a virtual ssa name
>
> On Wed, May 13, 2020 at 11:08 AM 易会战 <huizha...@foxmail.com> 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"<richard.guent...@gmail.com>
> > Date: Wed, May 13, 2020 15:00 PM
> > To: "易会战"<huizha...@foxmail.com>;
> > Cc: "gcc"<gcc@gcc.gnu.org>;
> > Subject: Re: how to find variable related to a virtual ssa name
> >
> > On Wed, May 13, 2020 at 6:03 AM 易会战 <huizha...@foxmail.com> 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"<richard.guent...@gmail.com>
> > > Date: Tue, May 12, 2020 22:20 PM
> > > To: "易会战"<huizha...@foxmail.com>;
> > > Cc: "gcc"<gcc@gcc.gnu.org>;
> > > Subject: Re: how to find variable related to a virtual ssa name
> > >
> > > On Tue, May 12, 2020 at 4:16 PM 易会战 <huizha...@foxmail.com> 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"<richard.guent...@gmail.com>
> > > > Date: Tue, May 12, 2020 22:02 PM
> > > > To: "易会战"<huizha...@foxmail.com>;
> > > > Cc: "gcc"<gcc@gcc.gnu.org>;
> > > > 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 <gcc@gcc.gnu.org> 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, 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 is a address pointing to global memory. But just
> > > > > from _3=ptr, cannot judge it.
> > > > > 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.
