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.
